ksh(1) User Commands ksh(1)NAME
ksh, rksh - KornShell, a standard/restricted command and programming
language
SYNOPSIS
/usr/bin/ksh [± abCefhikmnoprstuvx] [± o option]...
[arg]...
/usr/bin/ksh -c [± abCefhikmnoprstuvx]
[± o option]... command_string
[command_name [arg...]]
/usr/xpg4/bin/sh [± abCefhikmnoprstuvx]
[± o option]... [arg]...
/usr/xpg4/bin/sh -c [± abCefhikmnoprstuvx]
[± o option]... command_string
[command_name [arg...]]
/usr/bin/rksh [± abCefhikmnoprstuvx] [± o option]...
[arg]...
/usr/bin/rksh -c [± abCefhikmnoprstuvx]
[± o option]... command_string
[command_name [arg...]]
DESCRIPTION
The /usr/xpg4/bin/sh utility is a standards compliant shell. This util‐
ity provides all the functionality of /usr/bin/ksh, except in cases
where differences in behavior exist. See Arithmetic Expansions section
for details.
/usr/bin/ksh is a command and programming language that executes com‐
mands read from a terminal or a file. rksh is a restricted version of
the command interpreter ksh; it is used to set up login names and exe‐
cution environments whose capabilities are more controlled than those
of the standard shell. See the Invocation section for the meaning of
arguments to the shell.
Definitions
A metacharacter is one of the following characters:
; & ( ) | < > NEWLINE SPACE TAB
A blank is a TAB or a SPACE. An identifier is a sequence of letters,
digits, or underscores starting with a letter or underscore. Identi‐
fiers are used as names for functions and variables. A word is a
sequence of characters separated by one or more non-quoted metacharac‐
ters.
A command is a sequence of characters in the syntax of the shell lan‐
guage. The shell reads each command and carries out the desired action
either directly or by invoking separate utilities. A special-command is
a command that is carried out by the shell without creating a separate
process. Except for documented side effects, most special commands can
be implemented as separate utilities.
Commands
A simple-command is a sequence of blank-separated words which can be
preceded by a variable assignment list. See Environment. The first word
specifies the name of the command to be executed. Except as specified,
the remaining words are passed as arguments to the invoked command. The
command name is passed as argument 0 (see exec(2)). The value of a sim‐
ple-command is its exit status if it terminates normally. If it termi‐
nates abnormally due to receipt of a signal, the value is the signal
number plus 128. See signal.h(3HEAD) for a list of signal values. Obvi‐
ously, normal exit status values 129 to 255 cannot be distinguished
from abnormal exit caused by receiving signal numbers 1 to 127.
A pipeline is a sequence of one or more commands separated by |. The
standard output of each command but the last is connected by a pipe(2)
to the standard input of the next command. Each command is run as a
separate process; the shell waits for the last command to terminate.
The exit status of a pipeline is the exit status of the last command.
A list is a sequence of one or more pipelines separated by ;, &, &&, or
||, and optionally terminated by ;, &, or |&. Of these five symbols, ;,
&, and |& have equal precedence, which is lower than that of && and ||.
The symbols && and || also have equal precedence. A semicolon (;)
causes sequential execution of the preceding pipeline; an ampersand (&)
causes asynchronous execution of the preceding pipeline (that is, the
shell does not wait for that pipeline to finish). The symbol |& causes
asynchronous execution of the preceding command or pipeline with a two-
way pipe established to the parent shell.
The standard input and output of the spawned command can be written to
and read from by the parent shell using the -p option of the special
commands read and print described in Special Commands. The symbol &&
(||) causes the list following it to be executed only if the preceding
pipeline returns 0 (or a non-zero) value. An arbitrary number of new-
lines can appear in a list, instead of a semicolon, to delimit a com‐
mand.
A command is either a simple-command or one of the following. Unless
otherwise stated, the value returned by a command is that of the last
simple-command executed in the command.
for identifier [ in word ... ] ; do list ; done
Each time a for command is executed, identifier is set to the next
word taken from the in word list. If in word ... is omitted, then
the for command executes the do list once for each positional
parameter that is set. See Parameter Substitution. Execution ends
when there are no more words in the list.
select identifier [ in word ... ] ; do list ; done
A select command prints to standard error (file descriptor 2), the
set of words, each preceded by a number. If in word ... is omitted,
then the positional parameters are used instead. See Parameter Sub‐
stitution. The PS3 prompt is printed and a line is read from the
standard input. If this line consists of the number of one of the
listed words, then the value of the variable identifier is set to
the word corresponding to this number. If this line is empty the
selection list is printed again. Otherwise the value of the vari‐
able identifier is set to NULL. (See Blank Interpretation about
NULL). The contents of the line read from standard input is saved
in the shell variable REPLY. The list is executed for each selec‐
tion until a break or EOF is encountered. If the REPLY variable is
set to NULL by the execution of list, then the selection list is
printed before displaying the PS3 prompt for the next selection.
case word in [ pattern [ | pattern ] ) list ;; ] ... esac
A case command executes the list associated with the first pattern
that matches word. The form of the patterns is the same as that
used for file-name generation. See File Name Generation.
if list ; then list ; [ elif list ; then list ; ... ] [ else list ; ]
fi
The list following if is executed and, if it returns an exit status
of 0, the list following the first then is executed. Otherwise, the
list following elif is executed and, if its value is 0, the list
following the next then is executed. Failing that, the else list is
executed. If no else list or then list is executed, then the if
command returns 0 exit status.
while list ; do list ; done
until list ; do list ; done
A while command repeatedly executes the while list and, if the exit
status of the last command in the list is 0, executes the do list;
otherwise the loop terminates. If no commands in the do list are
executed, then the while command returns 0 exit status. until can
be used in place of while to negate the loop termination test.
(list)
Execute list in a separate environment. If two adjacent open paren‐
theses are needed for nesting, a space must be inserted to avoid
arithmetic evaluation.
{list}
list is simply executed. Unlike the metacharacters ( and ), { and }
are reserved words and must occur at the beginning of a line or
after a ; in order to be recognized.
[[expression]]
Evaluates expression and returns 0 exit status when expression is
true. See Conditional Expressions for a description of expression.
function identifier { list ;}
identifier( ) { list ;}
Define a function which is referenced by identifier. The body of
the function is the list of commands between { and }. See Func‐
tions.
time pipeline
The pipeline is executed and the elapsed time as well as the user
and system time are printed to standard error.
The following reserved words are only recognized as the first word of a
command and when not quoted:
! if then else elif fi case
esac for while until do done { }
function select time [[ ]]
Comments
A word beginning with # causes that word and all the following charac‐
ters up to a new-line to be ignored.
Aliasing
The first word of each command is replaced by the text of an alias if
an alias for this word has been defined. An alias name consists of any
number of characters excluding metacharacters, quoting characters, file
expansion characters, parameter and command substitution characters,
and =. The replacement string can contain any valid shell script
including the metacharacters listed above. The first word of each com‐
mand in the replaced text, other than any that are in the process of
being replaced, is tested for aliases. If the last character of the
alias value is a blank then the word following the alias is also be
checked for alias substitution. Aliases can be used to redefine special
builtin commands but cannot be used to redefine the reserved words
listed above. Aliases can be created, listed, and exported with the
alias command and can be removed with the unalias command. Exported
aliases remain in effect for scripts invoked by name, but must be
reinitialized for separate invocations of the shell. See Invocation. To
prevent infinite loops in recursive aliasing, if the shell is not cur‐
rently processing an alias of the same name, the word is replaced by
the value of the alias; otherwise, it is not be replaced.
Aliasing is performed when scripts are read, not while they are exe‐
cuted. Therefore, for an alias to take effect, the alias definition
command has to be executed before the command which references the
alias is read.
Aliases are frequently used as a short hand for full path names. An
option to the aliasing facility allows the value of the alias to be
automatically set to the full pathname of the corresponding command.
These aliases are called tracked aliases. The value of a tracked alias
is defined the first time the corresponding command is looked up and
becomes undefined each time the PATH variable is reset. These aliases
remain tracked so that the next subsequent reference redefines the
value. Several tracked aliases are compiled into the shell. The -h
option of the set command makes each referenced command name into a
tracked alias.
The following exported aliases are compiled into (and built-in to) the
shell but can be unset or redefined:
autoload='typeset −fu'
functions='typeset −f'
history='fc −l'
integer='typeset −i'
nohup='nohup '
r='fc −e −'
An example concerning trailing blank characters and reserved words fol‐
lows. If the user types:
$ alias foo="/bin/ls "
$ alias while="/"
the effect of executing:
$ while true
> do
> echo "Hello, World"
> done
is a never-ending sequence of Hello, World strings to the screen. How‐
ever, if the user types:
$ foo while
the result is an ls listing of /. Since the alias substitution for foo
ends in a space character, the next word is checked for alias substitu‐
tion. The next word, while, has also been aliased, so it is substituted
as well. Since it is not in the proper position as a command word, it
is not recognized as a reserved word.
If the user types:
$ foo; while
while retains its normal reserved-word properties.
Tilde Substitution
After alias substitution is performed, each word is checked to see if
it begins with an unquoted ~. If it does, then the word up to a / is
checked to see if it matches a user name. If a match is found, the ~
and the matched login name are replaced by the login directory of the
matched user. This is called a tilde substitution. If no match is
found, the original text is left unchanged. A ~ by itself, or in front
of a /, is replaced by $HOME. A ~ followed by a + or − is replaced by
$PWD and $OLDPWD, respectively.
In addition, tilde substitution is attempted when the value of a vari‐
able assignment begins with a ~.
Tilde Expansion
A tilde-prefix consists of an unquoted tilde character at the beginning
of a word, followed by all of the characters preceding the first
unquoted slash in the word, or all the characters in the word if there
is no slash. In an assignment, multiple tilde-prefixes can be used: at
the beginning of the word (that is, following the equal sign of the
assignment), following any unquoted colon or both. A tilde-prefix in an
assignment is terminated by the first unquoted colon or slash. If none
of the characters in the tilde-prefix are quoted, the characters in the
tilde-prefix following the tilde are treated as a possible login name
from the user database.
A portable login name cannot contain characters outside the set given
in the description of the LOGNAME environment variable. If the login
name is null (that is, the tilde-prefix contains only the tilde), the
tilde-prefix is replaced by the value of the variable HOME. If HOME is
unset, the results are unspecified. Otherwise, the tilde-prefix is
replaced by a pathname of the home directory associated with the login
name obtained using the getpwnam function. If the system does not rec‐
ognize the login name, the results are undefined.
Tilde expansion generally occurs only at the beginning of words, but an
exception based on historical practice has been included:
PATH=/posix/bin:~dgk/bin
is eligible for tilde expansion because tilde follows a colon and none
of the relevant characters is quoted. Consideration was given to pro‐
hibiting this behavior because any of the following are reasonable sub‐
stitutes:
PATH=$(printf %s ~karels/bin : ~bostic/bin)
for Dir in ~maart/bin ~srb/bin .
do
PATH=${PATH:+$PATH:}$Dir
done
With the first command, explicit colons are used for each directory. In
all cases, the shell performs tilde expansion on each directory because
all are separate words to the shell.
Expressions in operands such as:
make -k mumble LIBDIR=~chet/lib
do not qualify as shell variable assignments and tilde expansion is not
performed (unless the command does so itself, which make does not).
The special sequence $~ has been designated for future implementations
to evaluate as a means of forcing tilde expansion in any word.
Because of the requirement that the word not be quoted, the following
are not equivalent; only the last causes tilde expansion:
\~hlj/ ~h\lj/ ~"hlj"/ ~hlj\/ ~hlj/
The results of giving tilde with an unknown login name are undefined
because the KornShell ~+ and ~− constructs make use of this condition,
but, in general it is an error to give an incorrect login name with
tilde. The results of having HOME unset are unspecified because some
historical shells treat this as an error.
Command Substitution
The standard output from a command enclosed in parenthesis preceded by
a dollar sign (that is, $(command)) or a pair of grave accents (``) can
be used as part or all of a word. Trailing new-lines are removed. In
the second (archaic) form, the string between the quotes is processed
for special quoting characters before the command is executed. See
Quoting. The command substitution $(cat file) can be replaced by the
equivalent but faster $(<file). Command substitution of most special
commands that do not perform input/output redirection are carried out
without creating a separate process.
Command substitution allows the output of a command to be substituted
in place of the command name itself. Command substitution occurs when
the command is enclosed as follows:
$(command)
or (backquoted version):
`command`
The shell expands the command substitution by executing command in a
subshell environment and replacing the command substitution (the text
of command plus the enclosing $() or backquotes) with the standard out‐
put of the command, removing sequences of one or more newline charac‐
ters at the end of the substitution. Embedded newline characters before
the end of the output is not be removed; however, they can be treated
as field delimiters and eliminated during field splitting, depending on
the value of IFS and quoting that is in effect.
Within the backquoted style of command substitution, backslash shall
retain its literal meaning, except when followed by:
$ ` \
(dollar-sign, backquote, backslash). The search for the matching back‐
quote is satisfied by the first backquote found without a preceding
backslash. During this search, if a non-escaped backquote is encoun‐
tered within a shell comment, a here-document, an embedded command sub‐
stitution of the $(command) form, or a quoted string, undefined results
occur. A single- or double-quoted string that begins, but does not end,
within the `...` sequence produces undefined results.
With the $(command) form, all characters following the open parenthesis
to the matching closing parenthesis constitute the command. Any valid
shell script can be used for command, except:
o A script consisting solely of redirections produces unspeci‐
fied results.
o See the restriction on single subshells.
The results of command substitution are not field splitting and path‐
name expansion processed for further tilde expansion, parameter expan‐
sion, command substitution or arithmetic expansion. If a command sub‐
stitution occurs inside double-quotes, it is not be performed on the
results of the substitution.
Command substitution can be nested. To specify nesting within the back‐
quoted version, the application must precede the inner backquotes with
backslashes; for example:
`\`command\``
The $() form of command substitution solves a problem of inconsistent
behavior when using backquotes. For example:
┌───────────────────────────────────────────────────────────┐
│ Command Output │
├───────────────────────────────────────────────────────────┤
│echo '\$x' \$x │
│echo `echo '\$x'` $x │
│echo $(echo '\$x') \$x │
└───────────────────────────────────────────────────────────┘
Additionally, the backquoted syntax has historical restrictions on the
contents of the embedded command. While the new $() form can process
any kind of valid embedded script, the backquoted form cannot handle
some valid scripts that include backquotes. For example, these other‐
wise valid embedded scripts do not work in the left column, but do work
on the right:
┌───────────────────────────────────────────────────────────┐
│echo ` echo $( │
│cat <<eeof cat <<eeof │
│a here-doc with ` a here-doc with ) │
│eof eof │
│` ) │
│echo ` echo $( │
│echo abc # a comment with ` echo abc # a comment with ) │
│` ) │
│echo ` echo $( │
│echo '`' echo ')' │
│` ) │
└───────────────────────────────────────────────────────────┘
Because of these inconsistent behaviors, the backquoted variety of com‐
mand substitution is not recommended for new applications that nest
command substitutions or attempt to embed complex scripts.
If the command substitution consists of a single subshell, such as:
$( (command) )
a portable application must separate the $( and ( into two tokens (that
is, separate them with white space). This is required to avoid any
ambiguities with arithmetic expansion.
Arithmetic Expansion
An arithmetic expression enclosed in double parentheses preceded by a
dollar sign ( $((arithmetic-expression)) ) is replaced by the value of
the arithmetic expression within the double parenthesis. Arithmetic
expansion provides a mechanism for evaluating an arithmetic expression
and substituting its value. The format for arithmetic expansion is as
follows:
$((expression))
The expression is treated as if it were in double-quotes, except that a
double-quote inside the expression is not treated specially. The shell
expands all tokens in the expression for parameter expansion, command
substitution and quote removal.
Next, the shell treats this as an arithmetic expression and substitute
the value of the expression. The arithmetic expression is processed
according to the rules of the ISO C with the following exceptions:
o Only integer arithmetic is required.
o The sizeof() operator and the prefix and postfix ++ and −−
operators are not required.
o Selection, iteration, and jump statements are not supported.
o /usr/bin/ksh and /usr/bin/rksh treat prefix 0 through 9 as
decimal constants. See the following examples:
Command Result in /bin/ksh Result in /usr/xpg4/bin/sh
echo $((010+10)) 20 18
echo $((019+10)) 29 error
[ 10 —le $((011)) ] true false
As an extension, the shell can recognize arithmetic expressions beyond
those listed. If the expression is invalid, the expansion fails and the
shell writes a message to standard error indicating the failure.
A simple example using arithmetic expansion:
# repeat a command 100 times
x=100
while [ $x −gt 0 ]
do
command
x=$(($x−1))
done
Process Substitution
This feature is available in SunOS and only on versions of the UNIX
operating system that support the /dev/fd directory for naming open
files. Each command argument of the form <(list) or >(list) runs
process list asynchronously connected to some file in /dev/fd. The name
of this file becomes the argument to the command. If the form with > is
selected, then writing on this file provides input for list. If < is
used, then the file passed as an argument contains the output of the
list process. For example:
paste <(cut -f1 file1) <(cut -f3 file2) | tee >(process1) >(process2)
cuts fields 1 and 3 from the files file1 and file2, respectively,
pastes the results together, and sends it to the processes process1 and
process2, as well as putting it onto the standard output. The file,
which is passed as an argument to the command, is a UNIX pipe(2) so
programs that expect to lseek(2) on the file does not work.
Parameter Substitution
A parameter is an identifier, one or more digits, or any of the charac‐
ters *, @, #, ?, −, $, and !. A variable (a parameter denoted by an
identifier) has a value and zero or more attributes. variables can be
assigned values and attributes by using the typeset special command.
The attributes supported by the shell are described later with the
typeset special command. Exported variables pass values and attributes
to the environment.
The shell supports a one-dimensional array facility. An element of an
array variable is referenced by a subscript. A subscript is denoted by
a [, followed by an arithmetic expression, followed by a ]. See Arith‐
metic Evaluation. To assign values to an array, use set -A name value
.... The value of all subscripts must be in the range of 0 through
4095. Arrays need not be declared. Any reference to a variable with a
valid subscript is legal and an array is created if necessary. Refer‐
encing an array without a subscript is equivalent to referencing the
element 0. If an array identifier with subscript * or @ is used, then
the value for each of the elements is substituted (separated by a field
separator character).
The value of a variable can be assigned by writing:
name=value [ name=value ] ...
If the integer attribute, -i, is set for name, the value is subject to
arithmetic evaluation.
Positional parameters, parameters denoted by a number, can be assigned
values with the set special command. Parameter $0 is set from argument
zero when the shell is invoked. If parameter is one or more digits then
it is a positional parameter. A positional parameter of more than one
digit must be enclosed in braces.
Parameter Expansion
The format for parameter expansion is as follows:
${expression}
where expression consists of all characters until the matching }. Any }
escaped by a backslash or within a quoted string, and characters in
embedded arithmetic expansions, command substitutions and variable
expansions, are not examined in determining the matching }.
The simplest form for parameter expansion is:
${parameter}
The value, if any, of parameter is substituted.
The parameter name or symbol can be enclosed in braces, which are
optional except for positional parameters with more than one digit or
when parameter is followed by a character that could be interpreted as
part of the name. The matching closing brace are determined by counting
brace levels, skipping over enclosed quoted strings and command substi‐
tutions.
If the parameter name or symbol is not enclosed in braces, the expan‐
sion uses the longest valid name whether or not the symbol represented
by that name exists. When the shell is scanning its input to determine
the boundaries of a name, it is not bound by its knowledge of what
names are already defined. For example, if F is a defined shell vari‐
able, the command:
echo $Fred
does not echo the value of $F followed by red; it selects the longest
possible valid name, Fred, which in this case might be unset.
If a parameter expansion occurs inside double-quotes:
o Pathname expansion is not be performed on the results of the
expansion.
o Field splitting is not performed on the results of the
expansion, with the exception of @.
In addition, a parameter expansion can be modified by using one of the
following formats. In each case that a value of word is needed (based
on the state of parameter), word is subjected to tilde expansion,
parameter expansion, command substitution and arithmetic expansion. If
word is not needed, it is not expanded. The } character that delimits
the following parameter expansion modifications is determined as
described previously in this section and in dquote. (For example,
${foo-bar}xyz} would result in the expansion of foo followed by the
string xyz} if foo is set, else the string barxyz}).
${parameter:−word} Use Default Values. If parameter is unset or
null, the expansion of word is substituted.
Otherwise, the value of parameter is substi‐
tuted.
${parameter:=word} Assign Default Values. If parameter is unset
or null, the expansion of word is assigned to
parameter. In all cases, the final value of
parameter is substituted. Only variables, not
positional parameters or special parameters,
can be assigned in this way.
${parameter:?[word]} Indicate Error if Null or Unset. If parameter
is unset or null, the expansion of word (or a
message indicating it is unset if word is
omitted) is written to standard error and the
shell exits with a non-zero exit status. Oth‐
erwise, the value of parameter is substituted.
An interactive shell need not exit.
${parameter:+[word]} Use Alternative Value. If parameter is unset
or null, null is substituted. Otherwise, the
expansion of word is substituted.
In the parameter expansions shown previously, use of the colon in the
format results in a test for a parameter that is unset or null. Omis‐
sion of the colon results in a test for a parameter that is only unset.
The following two tables summarize the effect of the colon:
│ │
│parameter set and not null │parameter set and null
────────────────────┼────────────────────────────┼───────────────────────
${parameter:-word} │substitute parameter │substitute word
────────────────────┼────────────────────────────┼───────────────────────
${parameter−word} │substitute parameter │substitute null
────────────────────┼────────────────────────────┼───────────────────────
${parameter:=word} │substitute parameter │assign word
────────────────────┼────────────────────────────┼───────────────────────
${parameter=word} │substitute parameter │substitute parameter
────────────────────┼────────────────────────────┼───────────────────────
${parameter:?word} │substitute parameter │error, exit
────────────────────┼────────────────────────────┼───────────────────────
${parameter?word} │substitute parameter │substitute null
────────────────────┼────────────────────────────┼───────────────────────
${parameter:+word} │substitute word │substitute null
────────────────────┼────────────────────────────┼───────────────────────
${parameter+word} │substitute word │substitute word
│
│ parameter unset
─────────────────────────────┼─────────────────────────────
${parameter:-word} │substitute word
─────────────────────────────┴─────────────────────────────
${parameter−word} │substitute word
─────────────────────────────┼─────────────────────────────
${parameter:=word} │assign word
─────────────────────────────┼─────────────────────────────
${parameter=word} │assign null
─────────────────────────────┼─────────────────────────────
${parameter:?word} │error, exit
─────────────────────────────┼─────────────────────────────
${parameter?word} │error,exit
─────────────────────────────┼─────────────────────────────
${parameter:+word} │substitute null
─────────────────────────────┼─────────────────────────────
${parameter+word} │substitute null
In all cases shown with "substitute", the expression is replaced with
the value shown. In all cases shown with "assign", parameter is
assigned that value, which also replaces the expression.
${#parameter} String Length. The length in characters of the value
of parameter. If parameter is * or @, then all the
positional parameters, starting with $1, are substi‐
tuted (separated by a field separator character).
The following four varieties of parameter expansion provide for sub‐
string processing. In each case, pattern matching notation (see pat‐
mat), rather than regular expression notation, is used to evaluate the
patterns. If parameter is * or @, then all the positional parameters,
starting with $1, are substituted (separated by a field separator char‐
acter). Enclosing the full parameter expansion string in double-quotes
does not cause the following four varieties of pattern characters to be
quoted, whereas quoting characters within the braces has this effect.
${parameter%word} Remove Smallest Suffix Pattern. The word is
expanded to produce a pattern. The parameter
expansion then results in parameter, with the
smallest portion of the suffix matched by the
pattern deleted.
${parameter%%word} Remove Largest Suffix Pattern. The word is
expanded to produce a pattern. The parameter
expansion then results in parameter, with the
largest portion of the suffix matched by the pat‐
tern deleted.
${parameter#word} Remove Smallest Prefix Pattern. The word is
expanded to produce a pattern. The parameter
expansion then results in parameter, with the
smallest portion of the prefix matched by the
pattern deleted.
${parameter##word} Remove Largest Prefix Pattern. The word is
expanded to produce a pattern. The parameter
expansion then results in parameter, with the
largest portion of the prefix matched by the pat‐
tern deleted.
Examples:
${parameter:−word}
In this example, ls is executed only if x is null or unset. (The $(ls)
command substitution notation is explained in Command Substitution
above.)
${x:-$(ls)}
${parameter:=word}
unset X
echo ${X:=abc}
abc
${parameter:?word}
unset posix
echo ${posix:?}
sh: posix: parameter null or not set
${parameter:+word}
set a b c
echo ${3:+posix}
posix
${#parameter}
HOME=/usr/posix
echo ${#HOME}
10
${parameter%word}
x=file.c
echo ${x%.c}.o
file.o
${parameter%%word}
x=posix/src/std
echo ${x%%/*}
posix
${parameter#word}
x=$HOME/src/cmd
echo ${x#$HOME}
/src/cmd
${parameter##word}
x=/one/two/three
echo ${x##*/}
three
Parameters Set by Shell
The following parameters are automatically set by the shell:
# The number of positional parameters in decimal.
− Flags supplied to the shell on invocation or by the set com‐
mand.
? The decimal value returned by the last executed command.
$ The process number of this shell.
_ Initially, the value of _ is an absolute pathname of the
shell or script being executed as passed in the environment.
Subsequently it is assigned the last argument of the previ‐
ous command. This parameter is not set for commands which
are asynchronous. This parameter is also used to hold the
name of the matching MAIL file when checking for mail.
! The process number of the last background command invoked.
ERRNO The value of errno as set by the most recently failed system
call. This value is system dependent and is intended for
debugging purposes.
LINENO The line number of the current line within the script or
function being executed.
OLDPWD The previous working directory set by the cd command.
OPTARG The value of the last option argument processed by the
getopts special command.
OPTIND The index of the last option argument processed by the
getopts special command.
PPID The process number of the parent of the shell.
PWD The present working directory set by the cd command.
RANDOM Each time this variable is referenced, a random integer,
uniformly distributed between 0 and 32767, is generated. The
sequence of random numbers can be initialized by assigning a
numeric value to RANDOM.
REPLY This variable is set by the select statement and by the read
special command when no arguments are supplied.
SECONDS Each time this variable is referenced, the number of seconds
since shell invocation is returned. If this variable is
assigned a value, then the value returned upon reference is
the value that was assigned plus the number of seconds since
the assignment.
Variables Used by Shell
The following variables are used by the shell:
CDPATH The search path for the cd command.
COLUMNS If this variable is set, the value is used to define the
width of the edit window for the shell edit modes and
for printing select lists.
EDITOR If the value of this variable ends in emacs, gmacs, or
vi and the VISUAL variable is not set, then the corre‐
sponding option is turned on. See the set special com‐
mand.
ENV This variable, when and only when an interactive shell
is invoked, is subjected to parameter expansion by the
shell and the resulting value is used as a pathname of a
file containing shell commands to execute in the cur‐
rent environment. The file need not be executable. If
the expanded value of ENV is not an absolute pathname,
the results are unspecified. ENV is ignored if the
user's real and effective user IDs or real and effective
group IDs are different.
This variable can be used to set aliases and other items
local to the invocation of a shell. The file referred to
by ENV differs from $HOME/.profile in that .profile is
typically executed at session startup, whereas the ENV
file is executed at the beginning of each shell invoca‐
tion. The ENV value is interpreted in a manner similar
to a dot script, in that the commands are executed in
the current environment and the file needs to be read‐
able, but not executable. However, unlike dot scripts,
no PATH searching is performed. This is used as a guard
against Trojan Horse security breaches.
FCEDIT The default editor name for the fc command.
FPATH The search path for function definitions. By default,
the FPATH directories are searched after the PATH vari‐
able. If an executable file is found, then it is read
and executed in the current environment. FPATH is
searched before PATH when a function with the -u
attribute is referenced. The preset alias autoload
causes a function with the -u attribute to be created.
HISTFILE If this variable is set when the shell is invoked, then
the value is the pathname of the file that is used to
store the command history. See Command re-entry.
HISTSIZE If this variable is set when the shell is invoked, then
the number of previously entered commands that are
accessible by this shell is greater than or equal to
this number. The default is 128.
HOME The default argument (home directory) for the cd com‐
mand.
IFS Internal field separators, normally space, tab, and new-
line that are used to separate command words which
result from command or parameter substitution and for
separating words with the special command read. The
first character of the IFS variable is used to separate
arguments for the $* substitution. See Quoting.
LANG Provide a default value for the internationalization
variables that are unset or null. If any of the interna‐
tionalization variables contains an invalid setting, the
utility behaves as if none of the variables had been
defined.
LC_ALL This variable provides a default value for the LC_*
variables.
LC_COLLATE This variable determines the behavior of range expres‐
sions, equivalence classes and multi-byte character col‐
lating elements within pattern matching.
LC_CTYPE Determines how the shell handles characters. When
LC_CTYPE is set to a valid value, the shell can display
and handle text and filenames containing valid charac‐
ters for that locale. If LC_CTYPE (see environ(5)) is
not set in the environment, the operational behavior of
the shell is determined by the value of the LANG envi‐
ronment variable. If LC_ALL is set, its contents are
used to override both the LANG and the other LC_* vari‐
ables.
LC_MESSAGES This variable determines the language in which messages
should be written.
LINENO This variable is set by the shell to a decimal number
representing the current sequential line number (num‐
bered starting with 1) within a script or function
before it executes each command. If the user unsets or
resets LINENO, the variable can lose its special meaning
for the life of the shell. If the shell is not currently
executing a script or function, the value of LINENO is
unspecified.
LINES If this variable is set, the value is used to determine
the column length for printing select lists. Select
lists print vertically until about two-thirds of LINES
lines are filled.
MAIL If this variable is set to the name of a mail file and
the MAILPATH variable is not set, then the shell informs
the user of arrival of mail in the specified file.
MAILCHECK This variable specifies how often (in seconds) the shell
checks for changes in the modification time of any of
the files specified by the MAILPATH or MAIL variables.
The default value is 600 seconds. When the time has
elapsed the shell checks before issuing the next prompt.
MAILPATH A colon (:) separated list of file names. If this vari‐
able is set, then the shell informs the user of any mod‐
ifications to the specified files that have occurred
within the last MAILCHECK seconds. Each file name can be
followed by a ? and a message that is printed. The mes‐
sage undergoes parameter substitution with the variable
$_ defined as the name of the file that has changed. The
default message is you have mail in $_.
NLSPATH Determine the location of message catalogues for the
processing of LC_MESSAGES.
PATH The search path for commands. See Execution. The user
cannot change PATH if executing under rksh (except in
.profile).
PPID This variable is set by the shell to the decimal process
ID of the process that invoked the shell. In a subshell,
PPID is set to the same value as that of the parent of
the current shell. For example, echo $PPID and (echo
$PPID) would produce the same value.
PS1 The value of this variable is expanded for parameter
substitution to define the primary prompt string which
by default is ``$ ''. The character ! in the primary
prompt string is replaced by the command number. See
Command Re-entry. Two successive occurrences of ! pro‐
duces a single ! when the prompt string is printed.
PS2 Secondary prompt string, by default ``> ''.
PS3 Selection prompt string used within a select loop, by
default ``#? ''.
PS4 The value of this variable is expanded for parameter
substitution and precedes each line of an execution
trace. If omitted, the execution trace prompt is ``+ ''.
PWD Set by the shell to be an absolute pathname of the cur‐
rent working directory, containing no components of type
symbolic link, no components that are dot, and no compo‐
nents that are dot-dot when the shell is initialized. If
an application sets or unsets the value of PWD, the
behaviors of the cd and pwd utilities are unspecified
SHELL The pathname of the shell is kept in the environment. At
invocation, if the basename of this variable is rsh,
rksh, or krsh, then the shell becomes restricted.
TMOUT If set to a value greater than zero, the shell termi‐
nates if a command is not entered within the prescribed
number of seconds after issuing the PS1 prompt. The
shell can be compiled with a maximum bound for this
value which cannot be exceeded.
VISUAL If the value of this variable ends in emacs, gmacs, or
vi, then the corresponding option is turned on. See Spe‐
cial Command set.
The shell gives default values to PATH, PS1, PS2, PS3, PS4, MAILCHECK,
FCEDIT, TMOUT, and IFS, while HOME, SHELL, ENV, and MAIL are not set at
all by the shell (although HOME is set by login(1)). On some systems
MAIL and SHELL are also set by login.
Blank Interpretation
After parameter and command substitution, the results of substitutions
are scanned for the field separator characters (those found in IFS) and
split into distinct arguments where such characters are found. Explicit
null arguments ( "" ) or ('') are retained. Implicit null arguments
(those resulting from parameters that have no values) are removed.
File Name Generation
Following substitution, each command word is scanned for the characters
*, ?, and [ unless the -f option has been set. If one of these charac‐
ters appears, the word is regarded as a pattern. The word is replaced
with lexicographically sorted file names that match the pattern. If no
file name is found that matches the pattern, the word is left
unchanged. When a pattern is used for file name generation, the charac‐
ter period (.) at the start of a file name or immediately following a
/, as well as the character / itself, must be matched explicitly. A
file name beginning with a period is not matched with a pattern with
the period inside parentheses. That is, ls .@(r*) would locate a file
named .restore, but ls @(.r*) would not. In other instances of pattern
matching, the / and . are not treated specially.
* Matches any string, including the null string.
? Matches any single character.
[...] Matches any one of the enclosed characters. A pair of charac‐
ters separated by − matches any character lexically between
the pair, inclusive. If the first character following the
opening "[" is a "! ", then any character not enclosed is
matched. A − can be included in the character set by putting
it as the first or last character.
A pattern-list is a list of one or more patterns separated from each
other with a |. Composite patterns can be formed with one or more of
the following:
?(pattern-list) Optionally matches any one of the given patterns.
*(pattern-list) Matches zero or more occurrences of the given pat‐
terns.
+(pattern-list) Matches one or more occurrences of the given pat‐
terns.
@(pattern-list) Matches exactly one of the given patterns.
!(pattern-list) Matches anything, except one of the given patterns.
Quoting
Each of the metacharacters listed above (see Definitions) has a special
meaning to the shell and causes termination of a word unless quoted. A
character can be quoted (that is, made to stand for itself) by preced‐
ing it with a \. The pair \NEWLINE is removed. All characters enclosed
between a pair of single quote marks (' ') are quoted. A single quote
cannot appear within single quotes. Inside double quote marks (""),
parameter and command substitution occur and \ quotes the characters \,
`, ", and $. The meaning of $* and $@ is identical when not quoted or
when used as a parameter assignment value or as a file name. However,
when used as a command argument, $* is equivalent to ``$1d$2d...'',
where d is the first character of the IFS variable, whereas $@ is
equivalent to $1 $2 .... Inside grave quote marks (``), \ quotes the
characters \, ', and $. If the grave quotes occur within double quotes,
then \ also quotes the character ".
The special meaning of reserved words or aliases can be removed by
quoting any character of the reserved word. The recognition of function
names or special command names listed cannot be altered by quoting
them.
Arithmetic Evaluation
An ability to perform integer arithmetic is provided with the special
command let. Evaluations are performed using long arithmetic. Constants
are of the form [ base# ] n where base is a decimal number between two
and thirty-six representing the arithmetic base and n is a number in
that base. If base is omitted then base 10 is used.
An arithmetic expression uses the same syntax, precedence, and associa‐
tivity of expression as the C language. All the integral operators,
other than ++, -;, ?:, and , are supported. Variables can be referenced
by name within an arithmetic expression without using the parameter
substitution syntax. When a variable is referenced, its value is evalu‐
ated as an arithmetic expression.
An internal integer representation of a variable can be specified with
the -i option of the typeset special command. Arithmetic evaluation is
performed on the value of each assignment to a variable with the -i
attribute. If you do not specify an arithmetic base, the first assign‐
ment to the variable determines the arithmetic base. This base is used
when parameter substitution occurs.
Since many of the arithmetic operators require quoting, an alternative
form of the let command is provided. For any command which begins with
a ((, all the characters until a matching )) are treated as a quoted
expression. More precisely, ((...)) is equivalent to let "...".
Prompting
When used interactively, the shell prompts with the parameter expanded
value of PS1 before reading a command. If at any time a new-line is
typed and further input is needed to complete a command, then the sec‐
ondary prompt (that is, the value of PS2) is issued.
Conditional Expressions
A conditional expression is used with the [[ compound command to test
attributes of files and to compare strings. Word splitting and file
name generation are not performed on the words between [[ and ]]. Each
expression can be constructed from one or more of the following unary
or binary expressions:
-a file True, if file exists.
-b file True, if file exists and is a block special file.
-c file True, if file exists and is a character special
file.
-d file True, if file exists and is a directory.
-e file True, if file exists.
-f file True, if file exists and is an ordinary file.
-g file True, if file exists and has its setgid bit set.
-h file True, if file exists and is a symbolic link.
-k file True, if file exists and has its sticky bit set.
-n string True, if length of string is non-zero.
-o option True, if option named option is on.
-p file True, if file exists and is a fifo special file or
a pipe.
-r file True, if file exists and is readable by current
process.
-s file True, if file exists and has size greater than
zero.
-t fildes True, if file descriptor number fildes is open and
associated with a terminal device.
-u file True, if file exists and has its setuid bit set.
-w file True, if file exists and is writable by current
process.
-x file True, if file exists and is executable by current
process. If file exists and is a directory, then
the current process has permission to search in
the directory.
-z string True, if length of string is zero.
-L file True, if file exists and is a symbolic link.
-O file True, if file exists and is owned by the effective
user id of this process.
-G file True, if file exists and its group matches the
effective group id of this process.
-S file True, if file exists and is a socket.
file1 -nt file2 True, if file1 exists and is newer than file2.
file1 -ot file2 True, if file1 exists and is older than file2.
file1 -ef file2 True, if file1 and file2 exist and refer to the
same file.
string True if the string string is not the null string.
string = pattern True, if string matches pattern.
string != pattern True, if string does not match pattern.
string1 < string2 True, if string1 comes before string2 based on
strings interpreted as appropriate to the locale
setting for category LC_COLLATE.
string1 > string2 True, if string1 comes after string2 based on
strings interpreted as appropriate to the locale
setting for category LC_COLLATE.
exp1 -eq exp2 True, if exp1 is equal to exp2.
exp1 -ne exp2 True, if exp1 is not equal to exp2.
exp1 -lt exp2 True, if exp1 is less than exp2.
exp1 -gt exp2 True, if exp1 is greater than exp2.
exp1 -le exp2 True, if exp1 is less than or equal to exp2.
exp1 -ge exp2 True, if exp1 is greater than or equal to exp2.
In each of the above expressions, if file is of the form /dev/fd/n,
where n is an integer, then the test is applied to the open file whose
descriptor number is n.
A compound expression can be constructed from these primitives by using
any of the following, listed in decreasing order of precedence.
(expression) True, if expression is true. Used to
group expressions.
! expression True if expression is false.
expression1 && expression2 True, if expression1 and expression2 are
both true.
expression1 || expression2 True, if either expression1 or expres‐
sion2 is true.
Input/Output
Before a command is executed, its input and output can be redirected
using a special notation interpreted by the shell. The following can
appear anywhere in a simple-command or can precede or follow a command
and are not passed on to the invoked command. Command and parameter
substitution occur before word or digit is used except as noted. File
name generation occurs only if the pattern matches a single file, and
blank interpretation is not performed.
<word Use file word as standard input (file descriptor 0).
>word Use file word as standard output (file descriptor 1). If
the file does not exist then it is created. If the file
exists, and the noclobber option is on, this causes an
error; otherwise, it is truncated to zero length.
>|word Sames as >, except that it overrides the noclobber
option.
>>word Use file word as standard output. If the file exists,
output is appended to it (by first seeking to the EOF).
Otherwise, the file is created.
<>word Open file word for reading and writing as standard input.
<< [-]word The shell input is read up to a line that is the same as
word, or to an EOF. No parameter substitution, command
substitution, or file name generation is performed on
word. The resulting document, called a here-document,
becomes the standard input. If any character of word is
quoted, no interpretation is placed upon the characters
of the document. Otherwise, parameter and command substi‐
tution occur, \NEWLINE is ignored, and \ must be used to
quote the characters \, $, `, and the first character of
word. If − is appended to <<, then all leading tabs are
stripped from word and from the document.
<&digit The standard input is duplicated from file descriptor
digit (see dup(2)). Similarly for the standard output
using >&digit.
<&− The standard input is closed. Similarly for the standard
output using >&−.
<&p The input from the co-process is moved to standard input.
>&p The output to the co-process is moved to standard output.
If one of the above is preceded by a digit, then the file descriptor
number referred to is that specified by the digit (instead of the
default 0 or 1). For example:
... 2>&1
means file descriptor 2 is to be opened for writing as a duplicate of
file descriptor 1.
The order in which redirections are specified is significant. The shell
evaluates each redirection in terms of the (file descriptor, file)
association at the time of evaluation. For example:
... 1>fname 2>&1
first associates file descriptor 1 with file fname. It then associates
file descriptor 2 with the file associated with file descriptor 1 (that
is, fname). If the order of redirections were reversed, file descriptor
2 would be associated with the terminal (assuming file descriptor 1 had
been) and then file descriptor 1 would be associated with file fname.
If a command is followed by & and job control is not active, then the
default standard input for the command is the empty file /dev/null.
Otherwise, the environment for the execution of a command contains the
file descriptors of the invoking shell as modified by input/output
specifications.
Environment
The environment (see environ(5)) is a list of name-value pairs that is
passed to an executed program in the same way as a normal argument
list. The names must be identifiers and the values are character
strings. The shell interacts with the environment in several ways. On
invocation, the shell scans the environment and creates a variable for
each name found, giving it the corresponding value and marking it
export. Executed commands inherit the environment. If the user modifies
the values of these variables or creates new ones, using the export or
typeset -x commands, they become part of the environment. The environ‐
ment seen by any executed command is thus composed of any name-value
pairs originally inherited by the shell, whose values can be modified
by the current shell, plus any additions which must be noted in export
or typeset -x commands.
The environment for any simple-command or function can be augmented by
prefixing it with one or more variable assignments. A variable assign‐
ment argument is a word of the form identifier=value. Thus:
TERM=450 cmd args
and
(export TERM; TERM=450; cmd args)
are equivalent (as far as the above execution of cmd is concerned,
except for special commands listed that are preceded with an asterisk).
If the -k flag is set, all variable assignment arguments are placed in
the environment, even if they occur after the command name. The follow‐
ing first prints a=b c and then c:
echo a=b c
set −k echo
a=b c
This feature is intended for use with scripts written for early ver‐
sions of the shell and its use in new scripts is strongly discouraged.
It is likely to disappear someday.
Functions
The function reserved word, described in the Commands section above, is
used to define shell functions. Shell functions are read in and stored
internally. Alias names are resolved when the function is read. Func‐
tions are executed like commands with the arguments passed as posi‐
tional parameters. See Execution.
Functions execute in the same process as the caller and share all files
and present working directory with the caller. Traps caught by the
caller are reset to their default action inside the function. A trap
condition that is not caught or ignored by the function causes the
function to terminate and the condition to be passed on to the caller.
A trap on EXIT set inside a function is executed after the function
completes in the environment of the caller. This is true only for non-
POSIX-style functions, that is, functions declared as
function func
as opposed to POSIX-style functions, declared as
func()
Ordinarily, variables are shared between the calling program and the
function. However, the typeset special command used within a function
defines local variables whose scope includes the current function and
all functions it calls.
The special command return is used to return from function calls.
Errors within functions return control to the caller.
The names of all functions can be listed with typeset-f. typeset -f
lists all function names as well as the text of all functions. typeset
-f function-names lists the text of the named functions only. Functions
can be undefined with the -f option of the unset special command.
Ordinarily, functions are unset when the shell executes a shell script.
The -xf option of the typeset command allows a function to be exported
to scripts that are executed without a separate invocation of the
shell. Functions that need to be defined across separate invocations of
the shell should be specified in the ENV file with the -xf option of
typeset.
Function Definition Command
A function is a user-defined name that is used as a simple command to
call a compound command with new positional parameters. A function is
defined with a function definition command.
The format of a function definition command is as follows:
fname() compound-command[io-redirect ...]
The function is named fname; it must be a name. An implementation can
allow other characters in a function name as an extension. The imple‐
mentation maintains separate name spaces for functions and variables.
The () in the function definition command consists of two operators.
Therefore, intermixing blank characters with the fname, (, and ) is
allowed, but unnecessary.
The argument compound-command represents a compound command.
When the function is declared, none of the expansions in wordexp is
performed on the text in compound-command or io-redirect; all expan‐
sions is performed as normal each time the function is called. Simi‐
larly, the optional io-redirect redirections and any variable assign‐
ments within compound-command is performed during the execution of the
function itself, not the function definition.
When a function is executed, it has the syntax-error and variable-
assignment properties described for the special built-in utilities.
The compound-command is executed whenever the function name is speci‐
fied as the name of a simple command The operands to the command tempo‐
rarily becomes the positional parameters during the execution of the
compound-command; the special parameter # is also changed to reflect
the number of operands. The special parameter 0 is unchanged. When the
function completes, the values of the positional parameters and the
special parameter # is restored to the values they had before the func‐
tion was executed. If the special built-in return is executed in the
compound-command, the function completes and execution resumes with the
next command after the function call.
An example of how a function definition can be used wherever a simple
command is allowed:
# If variable i is equal to "yes",
# define function foo to be ls −l
#
[ "$i" = yes ] && foo() {
ls −l
}
The exit status of a function definition is 0 if the function was
declared successfully; otherwise, it is greater than zero. The exit
status of a function invocation is the exit status of the last command
executed by the function.
Jobs
If the monitor option of the set command is turned on, an interactive
shell associates a job with each pipeline. It keeps a table of current
jobs, printed by the jobs command, and assigns them small integer num‐
bers. When a job is started asynchronously with &, the shell prints a
line which looks like:
[1] 1234
indicating that the job, which was started asynchronously, was job num‐
ber 1 and had one (top-level) process, whose process id was 1234.
If you are running a job and wish to do something else you can press
the key ^Z (Control-Z) which sends a STOP signal to the current job.
The shell normally indicates that the job has been `Stopped', and print
another prompt. You can then manipulate the state of this job, putting
it in the background with the bg command, or run some other commands
and then eventually bring the job back into the foreground with the
foreground command fg. A ^Z takes effect immediately and is like an
interrupt in that pending output and unread input are discarded when it
is typed.
A job being run in the background stops if it tries to read from the
terminal. Background jobs are normally allowed to produce output, but
this can be disabled by giving the command "stty tostop". If you set
this tty option, then background jobs stop when they try to produce
output as they do when they try to read input.
There are several ways to refer to jobs in the shell. A job can be
referred to by the process id of any process of the job or by one of
the following:
%number The job with the given number.
%string Any job whose command line begins with string.
%?string Any job whose command line contains string.
%% Current job.
%+ Equivalent to %%.
%− Previous job.
The shell learns immediately whenever a process changes state. It nor‐
mally informs you whenever a job becomes blocked so that no further
progress is possible, but only just before it prints a prompt. This is
done so that it does not otherwise disturb your work.
When the monitor mode is on, each background job that completes trig‐
gers any trap set for CHLD.
When you try to leave the shell while jobs are running or stopped, you
are warned with the message, `You have stopped(running) jobs.' You can
use the jobs command to see what they are. If you do this or immedi‐
ately try to exit again, the shell does not warn you a second time, and
the stopped jobs is terminated. If you have jobs running for which the
nohup command was invoked and attempt to logout, you are warned with
the message:
You have jobs running.
You need to logout a second time to actually logout. However, your
background jobs continue to run.
Signals
The INT and QUIT signals for an invoked command are ignored if the com‐
mand is followed by & and the monitor option is not active. Otherwise,
signals have the values inherited by the shell from its parent. See the
trap special command section.
Execution
Each time a command is executed, the above substitutions are carried
out. If the command name matches one of the Special Commands listed, it
is executed within the current shell process. Next, the command name is
checked to see if it matches one of the user defined functions. If it
does, the positional parameters are saved and then reset to the argu‐
ments of the function call. When the function completes or issues a
return, the positional parameter list is restored and any trap set on
EXIT within the function is executed. The value of a function is the
value of the last command executed. A function is also executed in the
current shell process. If a command name is not a special command or a
user defined function, a process is created and an attempt is made to
execute the command using exec(2).
The shell variable PATH defines the search path for the directory con‐
taining the command. Alternative directory names are separated by a
colon (:). The default path is /bin:/usr/bin: (specifying /bin,
/usr/bin, and the current directory in that order). The current direc‐
tory can be specified by two or more adjacent colons, or by a colon at
the beginning or end of the path list. If the command name contains a /
then the search path is not used. Otherwise, each directory in the path
is searched for an executable file. If the file has execute permission
but is not a directory or an a.out file, it is assumed to be a file
containing shell commands. A sub-shell is spawned to read it. All non-
exported aliases, functions, and variables are removed in this case. A
parenthesized command is executed in a sub-shell without removing non-
exported quantities.
Command Re-entry
The text of the last HISTSIZE (default 128) commands entered from a
terminal device is saved in a history file. The file $HOME/.sh_history
is used if the HISTFILE variable is not set or if the file it names is
not writable. A shell can access the commands of all interactive shells
which use the same named HISTFILE. The special command fc is used to
list or edit a portion of this file. The portion of the file to be
edited or listed can be selected by number or by giving the first char‐
acter or characters of the command. A single command or range of com‐
mands can be specified. If you do not specify an editor program as an
argument to fc then the value of the variable FCEDIT is used. If FCEDIT
is not defined, then /bin/ed is used. The edited command(s) is printed
and re-executed upon leaving the editor. The editor name − is used to
skip the editing phase and to re-execute the command. In this case a
substitution parameter of the form old=new can be used to modify the
command before execution. For example, if r is aliased to 'fc -e -'
then typing 'r bad=good c' re-executes the most recent command which
starts with the letter c, replacing the first occurrence of the string
bad with the string good.
In-line Editing Option
Normally, each command line entered from a terminal device is simply
typed followed by a new-line (RETURN or LINEFEED). If either the emacs,
gmacs, or vi option is active, the user can edit the command line. To
be in either of these edit modes set the corresponding option. An edit‐
ing option is automatically selected each time the VISUAL or EDITOR
variable is assigned a value ending in either of these option names.
The editing features require that the user's terminal accept RETURN as
carriage return without line feed and that a space must overwrite the
current character on the screen.
The editing modes implement a concept where the user is looking through
a window at the current line. The window width is the value of COLUMNS
if it is defined, otherwise 80. If the window width is too small to
display the prompt and leave at least 8 columns to enter input, the
prompt is truncated from the left. If the line is longer than the win‐
dow width minus two, a mark is displayed at the end of the window to
notify the user. As the cursor moves and reaches the window boundaries
the window are centered about the cursor. The mark is a > if the line
extends on the right side of the window, < if the line extends on the
left, and * if the line extends on both sides of the window.
The search commands in each edit mode provide access to the history
file. Only strings are matched, not patterns, although a leading caret
(^) in the string restricts the match to begin at the first character
in the line.
emacs Editing Mode
This mode is entered by enabling either the emacs or gmacs option. The
only difference between these two modes is the way they handle ^T. To
edit, move the cursor to the point needing correction and then insert
or delete characters or words as needed. All the editing commands are
control characters or escape sequences. The notation for control char‐
acters is caret ( ^ ) followed by the character. For example, ^F is the
notation for control F. This is entered by depressing `f' while holding
down the CTRL (control) key. The SHIFT key is not depressed. (The nota‐
tion ^? indicates the DEL (delete) key.)
The notation for escape sequences is M- followed by a character. For
example, M-f (pronounced Meta f) is entered by depressing ESC (ascii
033) followed by `f'. (M-F would be the notation for ESC followed by
SHIFT (capital) `F'.)
All edit commands operate from any place on the line (not just at the
beginning). Neither the RETURN nor the LINEFEED key is entered after
edit commands except when noted.
^F Move cursor forward (right) one character.
M-f Move cursor forward one word. (The emacs editor's idea of
a word is a string of characters consisting of only let‐
ters, digits and underscores.)
^B Move cursor backward (left) one character.
M-b Move cursor backward one word.
^A Move cursor to start of line.
^E Move cursor to end of line.
^]char Move cursor forward to character char on current line.
M-^]char Move cursor backward to character char on current line.
^X^X Interchange the cursor and mark.
erase (User defined erase character as defined by the stty(1)
command, usually ^H or #.) Delete previous character.
^D Delete current character.
M-d Delete current word.
M-^H (Meta-backspace) Delete previous word.
M-h Delete previous word.
M-^? (Meta-DEL) Delete previous word (if your interrupt charac‐
ter is ^? (DEL, the default) then this command does not
work).
^T Transpose current character with next character in emacs
mode. Transpose two previous characters in gmacs mode.
^C Capitalize current character.
M-c Capitalize current word.
M-l Change the current word to lower case.
^K Delete from the cursor to the end of the line. If preceded
by a numerical parameter whose value is less than the cur‐
rent cursor position, then delete from given position up
to the cursor. If preceded by a numerical parameter whose
value is greater than the current cursor position, then
delete from cursor up to given cursor position.
^W Kill from the cursor to the mark.
M-p Push the region from the cursor to the mark on the stack.
kill (User defined kill character as defined by the stty(1)
command, usually ^G or @.) Kill the entire current line.
If two kill characters are entered in succession, all kill
characters from then on cause a line feed (useful when
using paper terminals).
^Y Restore last item removed from line. (Yank item back to
the line.)
^L Line feed and print current line.
^@ (null character) Set mark.
M-space (Meta space) Set mark.
J (New line) Execute the current line.
M (Return) Execute the current line.
eof End-of-file character, normally ^D, is processed as an
End-of-file only if the current line is null.
^P Fetch previous command. Each time ^P is entered the previ‐
ous command back in time is accessed. Moves back one line
when not on the first line of a multi-line command.
M-< Fetch the least recent (oldest) history line.
M-> Fetch the most recent (youngest) history line.
^N Fetch next command line. Each time ^N is entered the next
command line forward in time is accessed.
^Rstring Reverse search history for a previous command line con‐
taining string. If a parameter of zero is given, the
search is forward. string is terminated by a RETURN or NEW
LINE. If string is preceded by a ^, the matched line must
begin with string. If string is omitted, then the next
command line containing the most recent string is
accessed. In this case a parameter of zero reverses the
direction of the search.
^O Operate. Execute the current line and fetch the next line
relative to current line from the history file.
M-digits (Escape) Define numeric parameter, the digits are taken as
a parameter to the next command. The commands that accept
a parameter are ^F, ^B, erase, ^C, ^D, ^K, ^R, ^P, ^N, ^],
M-., M-^], M-_, M-b, M-c, M-d, M-f, M-h, M-l and M-^H.
M-letter Soft-key. Your alias list is searched for an alias by the
name _letter and if an alias of this name is defined, its
value is inserted on the input queue. The letter must not
be one of the above meta-functions.
M-[letter Soft-key. Your alias list is searched for an alias by the
name __letter and if an alias of this name is defined, its
value is inserted on the input queue. The can be used to
program functions keys on many terminals.
M−. The last word of the previous command is inserted on the
line. If preceded by a numeric parameter, the value of
this parameter determines which word to insert rather than
the last word.
M−_ Same as M−..
M−* An asterisk is appended to the end of the word and a file
name expansion is attempted.
M−ESC File name completion. Replaces the current word with the
longest common prefix of all filenames matching the cur‐
rent word with an asterisk appended. If the match is
unique, a / is appended if the file is a directory and a
space is appended if the file is not a directory.
M−= List files matching current word pattern if an asterisk
were appended.
^U Multiply parameter of next command by 4.
\ Escape next character. Editing characters, the user's
erase, kill and interrupt (normally ^?) characters can be
entered in a command line or in a search string if pre‐
ceded by a \. The \ removes the next character's editing
features (if any).
^V Display version of the shell.
M-# Insert a # at the beginning of the line and execute it.
This causes a comment to be inserted in the history file.
vi Editing Mode
There are two typing modes. Initially, when you enter a command you are
in the input mode. To edit, enter control mode by typing ESC (033) and
move the cursor to the point needing correction and then insert or
delete characters or words as needed. Most control commands accept an
optional repeat count prior to the command.
When in vi mode on most systems, canonical processing is initially
enabled and the command is echoed again if the speed is 1200 baud or
greater and it contains any control characters or less than one second
has elapsed since the prompt was printed. The ESC character terminates
canonical processing for the remainder of the command and the user can
then modify the command line. This scheme has the advantages of canoni‐
cal processing with the type-ahead echoing of raw mode.
If the option viraw is also set, the terminal always have canonical
processing disabled. This mode is implicit for systems that do not sup‐
port two alternate end of line delimiters, and can be helpful for cer‐
tain terminals.
Input Edit Commands
By default the editor is in input mode.
erase (User defined erase character as defined by the stty(1) com‐
mand, usually ^H or #.) Delete previous character.
^W Delete the previous blank separated word.
^D Terminate the shell.
^V Escape next character. Editing characters and the user's erase
or kill characters can be entered in a command line or in a
search string if preceded by a ^V. The ^V removes the next
character's editing features (if any).
\ Escape the next erase or kill character.
Motion Edit Commands
The following commands move the cursor:
[count]l Cursor forward (right) one character.
[count]w Cursor forward one alpha-numeric word.
[count]W Cursor to the beginning of the next word that follows a
blank.
[count]e Cursor to end of word.
[count]E Cursor to end of the current blank delimited word.
[count]h Cursor backward (left) one character.
[count]b Cursor backward one word.
[count]B Cursor to preceding blank separated word.
[count]| Cursor to column count.
[count]fc Find the next character c in the current line.
[count]Fc Find the previous character c in the current line.
[count]tc Equivalent to f followed by h.
[count]Tc Equivalent to F followed by l.
[count]; Repeats count times, the last single character find com‐
mand, f, F, t, or T.
[count], Reverses the last single character find command count
times.
0 Cursor to start of line.
^ Cursor to first non-blank character in line.
$ Cursor to end of line.
% Moves to balancing (, ), {, }, [, or ]. If cursor is not
on one of the above characters, the remainder of the line
is searched for the first occurrence of one of the above
characters first.
Search Edit Commands
These commands access your command history.
[count]k Fetch previous command. Each time k is entered the pre‐
vious command back in time is accessed.
[count]− Equivalent to k.
[count]j Fetch next command. Each time j is entered, the next
command forward in time is accessed.
[count]+ Equivalent to j.
[count]G The command number count is fetched. The default is the
least recent history command.
/string Search backward through history for a previous command
containing string. string is terminated by a RETURN or
NEWLINE. If string is preceded by a ^, the matched line
must begin with string. If string is NULL, the previous
string is used.
?string Same as / except that search is in the forward direc‐
tion.
n Search for next match of the last pattern to / or ? com‐
mands.
N Search for next match of the last pattern to / or ?, but
in reverse direction. Search history for the string
entered by the previous / command.
Text Modification Edit Commands
These commands modifies the line.
a Enter input mode and enter text after the current
character.
A Append text to the end of the line. Equivalent to $a.
[count]cmotion Delete current character through the character that
c[count]motion motion would move the cursor to and enter input mode.
If motion is c, the entire line is deleted and input
mode entered.
C Delete the current character through the end of line
and enter input mode. Equivalent to c$.
[count]s Delete count characters and enter input mode.
S Equivalent to cc.
D Delete the current character through the end of line.
Equivalent to d$.
[count]dmotion Delete current character through the character that
d[count]motion motion would move to. If motion is d, the entire line
is deleted.
i Enter input mode and insert text before the current
character.
I Insert text before the beginning of the line. Equiva‐
lent to 0i.
[count]P Place the previous text modification before the cur‐
sor.
[count]p Place the previous text modification after the cur‐
sor.
R Enter input mode and replace characters on the screen
with characters you type overlay fashion.
[count]rc Replace the count character(s) starting at the cur‐
rent cursor position with c, and advance the cursor.
[count]x Delete current character.
[count]X Delete preceding character.
[count]. Repeat the previous text modification command.
[count]~ Invert the case of the count character(s) starting at
the current cursor position and advance the cursor.
[count]_ Causes the count word of the previous command to be
appended and input mode entered. The last word is
used if count is omitted.
* Causes an * to be appended to the current word and
file name generation attempted. If no match is found,
it rings the bell. Otherwise, the word is replaced by
the matching pattern and input mode is entered.
\ Filename completion. Replaces the current word with
the longest common prefix of all filenames matching
the current word with an asterisk appended. If the
match is unique, a / is appended if the file is a
directory and a space is appended if the file is not
a directory.
Other Edit Commands
Miscellaneous commands.
[count]ymotion Yank current character through character that motion
y[count]motion would move the cursor to and puts them into the
delete buffer. The text and cursor are unchanged.
Y Yanks from current position to end of line. Equiva‐
lent to y$.
u Undo the last text modifying command.
U Undo all the text modifying commands performed on the
line.
[count]v Returns the command fc -e ${VISUAL:-${EDITOR:-vi}}
count in the input buffer. If count is omitted, then
the current line is used.
^L Line feed and print current line. Has effect only in
control mode.
J (New line) Execute the current line, regardless of
mode.
M (Return) Execute the current line, regardless of
mode.
# If the first character of the command is a #, then
this command deletes this # and each # that follows a
newline. Otherwise, sends the line after inserting a
# in front of each line in the command. Useful for
causing the current line to be inserted in the his‐
tory as a comment and removing comments from previous
comment commands in the history file.
= List the file names that match the current word if an
asterisk were appended it.
@letter Your alias list is searched for an alias by the name
_letter and if an alias of this name is defined, its
value is inserted on the input queue for processing.
Special Commands
The following simple-commands are executed in the shell process.
Input/Output redirection is permitted. Unless otherwise indicated, the
output is written on file descriptor 1 and the exit status, when there
is no syntax error, is 0. Commands that are preceded by one or two *
(asterisks) are treated specially in the following ways:
1. Variable assignment lists preceding the command remain in
effect when the command completes.
2. I/O redirections are processed after variable assignments.
3. Errors cause a script that contains them to abort.
4. Words, following a command preceded by ** that are in the
format of a variable assignment, are expanded with the same
rules as a variable assignment. This means that tilde sub‐
stitution is performed after the = sign and word splitting
and file name generation are not performed.
* : [ arg ... ]
The command only expands parameters.
* . file [ arg ... ]
Read the complete file then execute the commands. The commands are
executed in the current shell environment. The search path speci‐
fied by PATH is used to find the directory containing file. If any
arguments arg are given, they become the positional parameters.
Otherwise the positional parameters are unchanged. The exit status
is the exit status of the last command executed.
** alias [ -tx ] [ name[ =value ] ] ...
alias with no arguments prints the list of aliases in the form
name=value on standard output. An alias is defined for each name
whose value is given. A trailing space in value causes the next
word to be checked for alias substitution. The -t flag is used to
set and list tracked aliases. The value of a tracked alias is the
full pathname corresponding to the given name. The value becomes
undefined when the value of PATH is reset but the aliases remained
tracked. Without the -t flag, for each name in the argument list
for which no value is given, the name and value of the alias is
printed. The -x flag is used to set or print exported aliases. An
exported alias is defined for scripts invoked by name. The exit
status is non-zero if a name is given, but no value, and no alias
has been defined for the name.
bg [ %job... ]
This command is only on systems that support job control. Puts each
specified job into the background. The current job is put in the
background if job is not specified. See Jobs section above for a
description of the format of job.
* break [ n ]
Exit from the enclosed for, while, until, or select loop, if any.
If n is specified then break n levels. If n is greater than the
number of enclosing loops, the outermost enclosing loop shall be
exited.
* continue [ n ]
Resume the next iteration of the enclosed for, while, until, or
select loop. If n is specified then resume at the n-th enclosed
loop. If n is greater than the number of enclosing loops, the out‐
ermost enclosing loop shall be used.
cd [ -L ] [ -P ] [ arg ]
cd old new
This command can be in either of two forms. In the first form it
changes the current directory to arg. If arg is − the directory is
changed to the previous directory. The shell variable HOME is the
default arg. The environment variable PWD is set to the current
directory. If the PWD is changed, the OLDPWD environment variable
shall also be changed to the value of the old working directory,
that is, the current working directory immediately prior to the
call to change directory (cd). The shell variable CDPATH defines
the search path for the directory containing arg. Alternative
directory names are separated by a colon (:). The default path is
null (specifying the current directory). The current directory is
specified by a null path name, which can appear immediately after
the equal sign or between the colon delimiters anywhere else in the
path list. If arg begins with a / then the search path is not used.
Otherwise, each directory in the path is searched for arg. If
unsuccessful, cd attempts to change directories to the pathname
formed by the concatenation of the value of PWD, a slash character,
and arg.
-L Handles the operation dot-dot (..) logically. Symbolic link
components are not resolved before dot-dot components are
processed.
-P Handles the operand dot-dot physically. Symbolic link compo‐
nents are resolved before dot-dot components are processed.
If both -L and -P options are specified, the last option to be
invoked is used and the other is ignored. If neither -L nor -P is
specified, the operand is handled dot-dot logically.
The second form of cd substitutes the string new for the string old
in the current directory name, PWD, and tries to change to this new
directory. The cd command cannot be executed by rksh.
command [-p] [command_name] [argument ...]
command [-v | -V] command_name
The command utility causes the shell to treat the arguments as a
simple command, suppressing the shell function lookup. The -p flag
performs the command search using a default value for PATH that is
guaranteed to find all of the standard utilities. The -v flag
writes a string to standard output that indicates the pathname or
command that is used by the shell, in the current shell execution
environment, to invoke command_name. The -V flag writes a string to
standard output that indicates how the name given in the com‐
mand_name operand is interpreted by the shell, in the current shell
execution environment.
echo [ arg ... ]
See echo(1) for usage and description.
* eval [ arg ... ]
The arguments are read as input to the shell and the resulting com‐
mand(s) executed.
* exec [ arg ... ]
If arg is given, the command specified by the arguments is executed
in place of this shell without creating a new process. Input/output
arguments can appear and affect the current process. If no argu‐
ments are given the effect of this command is to modify file
descriptors as prescribed by the input/output redirection list. In
this case, any file descriptor numbers greater than 2 that are
opened with this mechanism are closed when invoking another pro‐
gram.
* exit [ n ]
Causes the calling shell or shell script to exit with the exit sta‐
tus specified by n. The value is the least significant 8 bits of
the specified status. If n is omitted then the exit status is that
of the last command executed. When exit occurs when executing a
trap, the last command refers to the command that executed before
the trap was invoked. An EOF also causes the shell to exit except
for a shell which has the ignoreeof option turned on. See set.
** export [ name[=value] ] ...
** export -p
The given names are marked for automatic export to the environment
of subsequently-executed commands.
When -p is specified, export writes to the standard output the
names and values of all exported variables in the following format:
"export %s=%s\n", name, value
if name is set, and:
"export %s\n", name
if name is unset.
The shell formats the output, including the proper use of quoting,
so that it is suitable for reinput to the shell as commands that
achieve the same exporting results, except for the following:
1. Read-only variables with values cannot be reset.
2. Variables that were unset at the time they were output
are not reset to the unset state if a value is assigned
to the variable between the time the state was saved and
the time at which the saved output is reinput to the
shell.
fc [ -e ename ] [ -nlr ] [ first [ last ] ]
fc -e - [ old=new ] [ command ]
fc -s [ old=new ] [ command ]
In the first form, a range of commands from first to last is
selected from the last HISTSIZE commands that were typed at the
terminal. The arguments first and last can be specified as a number
or as a string. A string is used to locate the most recent command
starting with the given string. A negative number is used as an
offset to the current command number. If the -l flag is selected,
the commands are listed on standard output. Otherwise, the editor
program ename is invoked on a file containing these keyboard com‐
mands. If ename is not supplied, then the value of the variable
FCEDIT (default /bin/ed) is used as the editor. When editing is
complete, the edited command(s) is executed. If last is not speci‐
fied then it is set to first. If first is not specified the default
is the previous command for editing and −16 for listing. The flag
-r reverses the order of the commands and the flag -n suppresses
command numbers when listing. In the second form the command is re-
executed after the substitution old=new is performed. If there is
not a command argument, the most recent command typed at this ter‐
minal is executed.
fg [ %job... ]
This command is only on systems that support job control. Each job
specified is brought to the foreground. Otherwise, the current job
is brought into the foreground. See "Jobs" section above for a
description of the format of job.
getopts optstring name [ arg ... ]
Checks arg for legal options. If arg is omitted, the positional
parameters are used. An option argument begins with a + or a −. An
option not beginning with + or − or the argument - ends the
options. optstring contains the letters that getopts recognizes.
If a letter is followed by a :, that option is expected to have an
argument. The options can be separated from the argument by blanks.
getopts places the next option letter it finds inside variable name
each time it is invoked with a + prepended when arg begins with a
+. The index of the next arg is stored in OPTIND. The option argu‐
ment, if any, gets stored in OPTARG.
A leading : in optstring causes getopts to store the letter of an
invalid option in OPTARG, and to set name to ? for an unknown
option and to : when a required option is missing. Otherwise,
getopts prints an error message. The exit status is non-zero when
there are no more options. See getoptcvt(1) for usage and descrip‐
tion.
getopts supports both traditional single-character short options
and long options defined by Sun's Command Line Interface Paradigm
(CLIP).
Each long option is an alias for a short option and is specified in
parentheses following its equivalent short option. For example,
you can specify the long option file as an alias for the short
option f using the following script line:
getopts "f(file)" opt
Precede long options on the command line with -- or ++. In the
example above, --file on the command line would be the equivalent
of -f, and ++file on the command line would be the equivalent of
+f.
Each short option can have multiple long option equivalents,
although this is in violation of the CLIP specification and should
be used with caution. You must enclose each long option equivalent
parentheses, as follows:
getopts "f:(file)(input-file)o:(output-file)"
In the above example, both --file and --input-file are the equiva‐
lent of -f, and --output-file is the equivalent of -o.
The variable name is always set to a short option. When a long
option is specified on the command line, name is set to the short-
option equivalent.
hash [ name ... ]
hash [ -r ]
For each name, the location in the search path of the command spec‐
ified by name is determined and remembered by the shell. The -r
option causes the shell to forget all remembered locations. If no
arguments are given, information about remembered commands is pre‐
sented. Hits is the number of times a command has been invoked by
the shell process. Cost is a measure of the work required to
locate a command in the search path. If a command is found in a
relative directory in the search path, after changing to that
directory, the stored location of that command is recalculated.
Commands for which this is done are indicated by an asterisk (*)
adjacent to the hits information. Cost is incremented when the
recalculation is done.
jobs [ -lnp ] [ %job ... ]
Lists information about each given job; or all active jobs if job
is omitted. The -l flag lists process ids in addition to the normal
information. The -n flag displays only jobs that have stopped or
exited since last notified. The -p flag causes only the process
group to be listed. See Jobs section above and jobs(1) for a
description of the format of job.
kill [ -sig ] %job ...
kill [ -sig ] pid ...
kill -l
Sends either the TERM (terminate) signal or the specified signal to
the specified jobs or processes. Signals are either given by number
or by names (as given in signal.h(3HEAD) stripped of the prefix
``SIG'' with the exception that SIGCHD is named CHLD). If the sig‐
nal being sent is TERM (terminate) or HUP (hangup), then the job or
process is sent a CONT (continue) signal if it is stopped. The
argument job can be the process id of a process that is not a mem‐
ber of one of the active jobs. See Jobs for a description of the
format of job. In the second form, kill -l, the signal numbers and
names are listed.
let arg...
Each arg is a separate arithmetic expression to be evaluated. See
the Arithmetic Evaluation section above, for a description of
arithmetic expression evaluation.
The exit status is 0 if the value of the last expression is non-
zero, and 1 otherwise.
login argument ...
Equivalent to `exec login argument....' See login(1) for usage and
description.
* newgrp [ arg ... ]
Equivalent to exec /bin/newgrp arg ....
print [ -Rnprsu[n ] ] [ arg ... ]
The shell output mechanism. With no flags or with flag − or -, the
arguments are printed on standard output as described by echo(1).
The exit status is 0, unless the output file is not open for writ‐
ing.
-n Suppresses NEWLINE from being added to the output.
-R | -r Raw mode. Ignores the escape conventions of echo. The
-R option prints all subsequent arguments and options
other than -n.
-p Writes the arguments to the pipe of the process spawned
with |& instead of standard output.
-s Writes the arguments to the history file instead of
standard output.
-u [ n ] Specifies a one digit file descriptor unit number n on
which the output is placed. The default is 1.
pwd [ -L | -P ]
Writes to the standard output an absolute pathname of the current
working directory, which does not contain the filenames dot (.) or
dot-dot (..).
-L If the PWD environment variable contains an absolute pathname
of the current directory that does not contain the filenames
dot or dot-dot, pwd writes this pathname to standard output.
Otherwise, the -L option behaves like the -P option.
-P The absolute pathname written shall not contain filenames
that, in the context of the pathname, refer to files of type
symbolic link.
If both -L and -P are specified, the last one applies. If neither
-L nor -P is specified, pwd behaves as if -L had been specified.
read [ -prsu[ n ] ] [ name?prompt ] [ name ... ]
The shell input mechanism. One line is read and is broken up into
fields using the characters in IFS as separators. The escape char‐
acter, (\), is used to remove any special meaning for the next
character and for line continuation. In raw mode, -r, the \ charac‐
ter is not treated specially. The first field is assigned to the
first name, the second field to the second name, etc., with left‐
over fields assigned to the last name. The -p option causes the
input line to be taken from the input pipe of a process spawned by
the shell using |&. If the -s flag is present, the input is saved
as a command in the history file. The flag -u can be used to spec‐
ify a one digit file descriptor unit n to read from. The file
descriptor can be opened with the exec special command. The default
value of n is 0. If name is omitted then REPLY is used as the
default name. The exit status is 0 unless the input file is not
open for reading or an EOF is encountered. An EOF with the -p
option causes cleanup for this process so that another can be
spawned. If the first argument contains a ?, the remainder of this
word is used as a prompt on standard error when the shell is inter‐
active. The exit status is 0 unless an EOF is encountered.
** readonly [ name[=value] ] ...
** readonly -p
The given names are marked readonly and these names cannot be
changed by subsequent assignment.
When -p is specified, readonly writes to the standard output the
names and values of all read-only variables, in the following for‐
mat:
"readonly %s=%s\n", name, value
if name is set, and:
"readonly $s\n", name
if name is unset.
The shell formats the output, including the proper use of quoting,
so that it is suitable for reinput to the shell as commands that
achieve the same value and readonly attribute-setting results in a
shell execution environment in which:
1. Variables with values set at the time they were output
do not have the readonly attribute set.
2. Variables that were unset at the time they were output
do not have a value at the time at which the saved out‐
put is reinput to the shell.
* return [ n ]
Causes a shell function or '.' script to return to the invoking
script with the return status specified by n. The value is the
least significant 8 bits of the specified status. If n is omitted
then the return status is that of the last command executed. If
return is invoked while not in a function or a '.' script, then it
is the same as an exit.
set [ ±abCefhkmnopstuvx ] [ ±o option ]... [ ±A name ] [ arg ... ]
The flags for this command have meaning as follows:
-A Array assignment. Unsets the variable name and assigns
values sequentially from the list arg. If +A is used,
the variable name is not unset first.
-a All subsequent variables that are defined are automati‐
cally exported.
-b Causes the shell to notify the user asynchronously of
background job completions. The following message is
written to standard error:
"[%d]%c %s%s\n", <job-number>, <current>, <status>, \
<job-name>
where the fields are as follows:
<current> The character + identifies the job that
would be used as a default for the fg
or bg utilities. This job can also be
specified using the job_id %+ or %%.
The character − identifies the job that
would become the default if the current
default job were to exit; this job can
also be specified using the job_id %−.
For other jobs, this field is a space
character. At most one job can be iden‐
tified with + and at most one job can
be identified with −. If there is any
suspended job, then the current job is
a suspended job. If there are at least
two suspended jobs, then the previous
job is also a suspended job.
<job-number> A number that can be used to identify
the process group to the wait, fg, bg,
and kill utilities. Using these utili‐
ties, the job can be identified by pre‐
fixing the job number with %.
<status> Unspecified.
<job-name> Unspecified.
When the shell notifies the user a job has been com‐
pleted, it can remove the job's process ID from the
list of those known in the current shell execution
environment. Asynchronous notification is not enabled
by default.
-C Prevents existing files from being overwritten by the
shell's > redirection operator. The >| redirection
operator overrides this noclobber option for an indi‐
vidual file.
-e If a command has a non-zero exit status, executes the
ERR trap, if set, and exit. This mode is disabled while
reading profiles.
-f Disables file name generation.
-h Each command becomes a tracked alias when first encoun‐
tered.
-k All variable assignment arguments are placed in the
environment for a command, not just those that precede
the command name.
-m Background jobs runs in a separate process group and a
line prints upon completion. The exit status of back‐
ground jobs is reported in a completion message. On
systems with job control, this flag is turned on auto‐
matically for interactive shells.
-n Reads commands and check them for syntax errors, but do
not execute them. Ignored for interactive shells.
-o Writes the current option settings to standard output
in a format that is suitable for reinput to the shell
as commands that achieve the same option settings.
-o The following argument can be one of the following
option names:
allexport Same as -a.
errexit Same as -e.
bgnice All background jobs are run at a lower
priority. This is the default mode.
emacs Puts you in an emacs style in-line editor
for command entry.
gmacs Puts you in a gmacs style in-line editor
for command entry.
ignoreeof The shell does not exit onEOF. The com‐
mand exit must be used.
keyword Same as -k.
markdirs All directory names resulting from file
name generation have a trailing /
appended.
monitor Same as -m.
noclobber Prevents redirection > from truncating
existing files. Require >| to truncate a
file when turned on. Equivalent to -C.
noexec Same as -n.
noglob Same as -f.
nolog Do not save function definitions in his‐
tory file.
notify Equivalent to -b.
nounset Same as -u.
privileged Same as -p.
verbose Same as -v.
trackall Same as -h.
vi Puts you in insert mode of a vi style in-
line editor until you hit escape charac‐
ter 033. This puts you in control mode. A
return sends the line.
viraw Each character is processed as it is
typed in vi mode.
xtrace Same as -x.
If no option name is supplied, the current option set‐
tings are printed.
-p Disables processing of the $HOME/.profile file and uses
the file /etc/suid_profile instead of the ENV file.
This mode is on whenever the effective uid is not equal
to the real uid, or when the effective gid is not equal
to the real gid. Turning this off causes the effective
uid and gid to be set to the real uid and gid.
-s Sorts the positional parameters lexicographically.
-t Exits after reading and executing one command.
-u Treats unset parameters as an error when substituting.
-v Prints shell input lines as they are read.
-x Prints commands and their arguments as they are exe‐
cuted.
− Turns off -x and -v flags and stops examining arguments
for flags.
−− Does not change any of the flags. Useful in setting $1
to a value beginning with −. If no arguments follow
this flag then the positional parameters are unset.
Using + rather than − causes these flags to be turned
off. These flags can also be used upon invocation of
the shell. The current set of flags can be found in $−.
Unless -A is specified, the remaining arguments are
positional parameters and are assigned, in order, to $1
$2 .... If no arguments are given, the names and values
of all variables are printed on the standard output.
* shift [ n ]
The positional parameters from $n+1 $n+1 ... are renamed $1 ...,
default n is 1. The parameter n can be any arithmetic expression
that evaluates to a non-negative number less than or equal to $#.
stop%jobid ...
stop pid ...
stop stops the execution of a background job(s) by using its jobid,
or of any process by using its pid. See ps(1).
suspend
Stops the execution of the current shell (but not if it is the
login shell).
test expression
Evaluates conditional expressions. See Conditional Expressions sec‐
tion above and test(1) for usage and description.
* times
Prints the accumulated user and system times for the shell and for
processes run from the shell.
* trap [ arg sig ... ]
arg is a command to be read and executed when the shell receives
signal(s) sig. arg is scanned once when the trap is set and once
when the trap is taken. sig can be specified as a signal number or
signal name. trap commands are executed in order of signal number.
Any attempt to set a trap on a signal number that was ignored on
entry to the current shell is ineffective.
If arg is −, the shell resets each sig to the default value. If arg
is null (''), the shell ignores each specified sig if it arises.
Otherwise, arg is read and executed by the shell when one of the
corresponding sigs arises. The action of the trap overrides a pre‐
vious action (either default action or one explicitly set). The
value of $? after the trap action completes is the value it had
before the trap was invoked.
sig can be EXIT, 0 (equivalent to EXIT) or a signal specified using
a symbolic name, without the SIG prefix, for example, HUP, INT,
QUIT, TERM. If sig is 0 or EXIT and the trap statement is executed
inside the body of a function, then the command arg is executed
after the function completes. If sig is 0 or EXIT for a trap set
outside any function, the command arg is executed on exit from the
shell. If sig is ERR, arg is executed whenever a command has a non-
zero exit status. If sig is DEBUG, arg is executed after each com‐
mand.
The environment in which the shell executes a trap on EXIT is iden‐
tical to the environment immediately after the last command exe‐
cuted before the trap on EXIT was taken.
Each time the trap is invoked, arg is processed in a manner equiva‐
lent to eval "$arg".
Signals that were ignored on entry to a non-interactive shell can‐
not be trapped or reset, although no error need be reported when
attempting to do so. An interactive shell can reset or catch sig‐
nals ignored on entry. Traps remain in place for a given shell
until explicitly changed with another trap command.
When a subshell is entered, traps are set to the default args. This
does not imply that the trap command cannot be used within the sub‐
shell to set new traps.
The trap command with no arguments writes to standard output a list
of commands associated with each sig. The format is:
trap −− %s %s ... <arg>, <sig> ...
The shell formats the output, including the proper use of quoting,
so that it is suitable for reinput to the shell as commands that
achieve the same trapping results. For example:
save_traps=$(trap)
...
eval "$save_traps"
If the trap name or number is invalid, a non-zero exit status is
returned. Otherwise, 0 is returned. For both interactive and non-
interactive shells, invalid signal names or numbers are not consid‐
ered a syntax error and dol not cause the shell to abort.
Traps are not processed while a job is waiting for a foreground
process. Thus, a trap on CHLD won't be executed until the fore‐
ground job terminates.
type name ...
For each name, indicates how it would be interpreted if used as a
command name.
** typeset [ ±HLRZfilrtux[n] ] [ name[=value ] ] ...
Sets attributes and values for shell variables and functions. When
typeset is invoked inside a function, a new instance of the vari‐
ables name is created. The variables value and type are restored
when the function completes. The following list of attributes can
be specified:
-H This flag provides UNIX to host-name file mapping on non-UNIX
machines.
-L Left justifies and removes leading blanks from value. If n is
non-zero it defines the width of the field. Otherwise, it is
determined by the width of the value of first assignment.
When the variable is assigned to, it is filled on the right
with blanks or truncated, if necessary, to fit into the
field. Leading zeros are removed if the -Z flag is also set.
The -R flag is turned off.
-R Right justifies and fills with leading blanks. If n is non-
zero it defines the width of the field, otherwise it is
determined by the width of the value of first assignment. The
field is left filled with blanks or truncated from the end if
the variable is reassigned. The -L flag is turned off.
-Z Right justifies and fills with leading zeros if the first
non-blank character is a digit and the -L flag has not been
set. If n is non-zero it defines the width of the field. Oth‐
erwise, it is determined by the width of the value of first
assignment.
-f The names refer to function names rather than variable names.
No assignments can be made and the only other valid flags are
-t, -u, and -x. The flag -t turns on execution tracing for
this function. The flag -u causes this function to be marked
undefined. The FPATH variable is searched to find the func‐
tion definition when the function is referenced. The flag -x
allows the function definition to remain in effect across
shell procedures invoked by name.
-i Parameter is an integer. This makes arithmetic faster. If n
is non-zero it defines the output arithmetic base; otherwise,
the first assignment determines the output base.
-l All upper-case characters are converted to lower-case. The
upper-case flag, -u is turned off.
-r The given names are marked readonly and these names cannot be
changed by subsequent assignment.
-t Tags the variables. Tags are user definable and have no spe‐
cial meaning to the shell.
-u All lower-case characters are converted to upper-case charac‐
ters. The lower-case flag, -l is turned off.
-x The given names are marked for automatic export to the envi‐
ronment of subsequently-executed commands.
The -i attribute cannot be specified along with -R, -L, -Z, or -f.
Using + rather than − causes these flags to be turned off. If no
name arguments are given but flags are specified, a list of names
(and optionally the values) of the variables which have these flags
set is printed. (Using + rather than − keeps the values from being
printed.) If no names and flags are given, the names and attributes
of all variables are printed.
ulimit [ -HSacdfnstv ] [ limit ]
Sets or displays a resource limit. The available resources limits
are listed in the following section. Many systems do not contain
one or more of these limits. The limit for a specified resource is
set when limit is specified. The value of limit can be a number in
the unit specified with each resource, or the value unlimited. The
H and S flags specify whether the hard limit or the soft limit for
the given resource is set. A hard limit cannot be increased once it
is set. A soft limit can be increased up to the value of the hard
limit. If neither the H or S options is specified, the limit
applies to both. The current resource limit is printed when limit
is omitted. In this case, the soft limit is printed unless H is
specified. When more than one resource is specified, the limit name
and unit is printed before the value.
-a Lists all of the current resource limits.
-c The number of 512-byte blocks on the size of core dumps.
-d The number of K-bytes on the size of the data area.
-f The number of 512-byte blocks on files written by child pro‐
cesses (files of any size can be read).
-n The number of file descriptors plus 1.
-s The number of K-bytes on the size of the stack area.
-t The number of seconds to be used by each process.
-v The number of K-bytes for virtual memory.
If no option is given, -f is assumed.
umask [-S] [ mask ]
The user file-creation mask is set to mask (see umask(2)). mask can
either be an octal number or a symbolic value as described in
chmod(1). If a symbolic value is given, the new umask value is the
complement of the result of applying mask to the complement of the
previous umask value. If mask is omitted, the current value of the
mask is printed. The -S flag produces symbolic output.
unalias name ...
unalias -a
The aliases given by the list of names are removed from the alias
list. The -a option removes all alias definitions from the current
execution environment.
unset [ -f ] name ...
The variables given by the list of names are unassigned, that is,
their values and attributes are erased. readonly variables cannot
be unset. If the -f, flag is set, then the names refer to function
names. Unsetting ERRNO, LINENO, MAILCHECK, OPTARG, OPTIND, RANDOM,
SECONDS, TMOUT, and _ removes their special meaning even if they
are subsequently assigned to.
* wait [ job ]
Waits for the specified job and report its termination status. If
job is not given then all currently active child processes are
waited for. The exit status from this command is that of the
process waited for. See Jobs for a description of the format of
job.
whence [ -pv ] name ...
For each name, indicates how it would be interpreted if used as a
command name.
The -v flag produces a more verbose report.
The -p flag does a path search for name even if name is an alias, a
function, or a reserved word.
Invocation
If the shell is invoked by exec(2), and the first character of argument
zero ($0) is −, then the shell is assumed to be a login shell and com‐
mands are read from /etc/profile and then from either .profile in the
current directory or $HOME/.profile, if either file exists. Next, com‐
mands are read from the file named by performing parameter substitution
on the value of the environment variable ENV if the file exists. If the
-s flag is not present and arg is, then a path search is performed on
the first arg to determine the name of the script to execute. The
script arg must have read permission and any setuid and setgid settings
are ignored. If the script is not found on the path, arg is processed
as if it named a builtin command or function. Commands are then read
as described as follows. The following flags are interpreted by the
shell when it is invoked:
-c Reads commands from the command_string operand. Sets the value of
special parameter 0 from the value of the command_name operand
and the positional parameters ($1, $2, and so on) in sequence
from the remaining arg operands. No commands are read from the
standard input.
-s If the -s flag is present or if no arguments remain, commands are
read from the standard input. Shell output, except for the output
of the Special Commands listed above, is written to file descrip‐
tor 2.
-i If the -i flag is present or if the shell input and output are
attached to a terminal (as told by ioctl(2)), then this shell is
interactive. In this case, TERM is ignored (so that kill 0 does
not kill an interactive shell) and INTR is caught and ignored (so
that wait is interruptible). In all cases, QUIT is ignored by the
shell.
-r If the -r flag is present the shell is a restricted shell.
The remaining flags and arguments are described under the set command
above.
rksh Only
rksh is used to set up login names and execution environments whose
capabilities are more controlled than those of the standard shell. The
actions of rksh are identical to those of ksh, except that the follow‐
ing are disallowed:
o changing directory (see cd(1))
o setting the value of SHELL, ENV, or PATH
o specifying path or command names containing /
o redirecting output (>, >|, <>, and >>)
o changing group (see newgrp(1)).
The restrictions above are enforced after .profile and the ENV files
are interpreted.
When a command to be executed is found to be a shell procedure, rksh
invokes ksh to execute it. Thus, it is possible to provide to the end-
user shell procedures that have access to the full power of the stan‐
dard shell, while imposing a limited menu of commands; this scheme
assumes that the end-user does not have write and execute permissions
in the same directory.
The net effect of these rules is that the writer of the .profile has
complete control over user actions, by performing guaranteed setup
actions and leaving the user in an appropriate directory (probably not
the login directory).
The system administrator often sets up a directory of commands (that
is, /usr/rbin) that can be safely invoked by rksh.
ERRORS
Errors detected by the shell, such as syntax errors, cause the shell to
return a non-zero exit status. Otherwise, the shell returns the exit
status of the last command executed (see also the exit command above).
If the shell is being used non-interactively then execution of the
shell file is abandoned. Run time errors detected by the shell are
reported by printing the command or function name and the error condi‐
tion. If the line number that the error occurred on is greater than
one, then the line number is also printed in square brackets ([]) after
the command or function name.
For a non-interactive shell, an error condition encountered by a spe‐
cial built-in or other type of utility causes the shell to write a
diagnostic message to standard error and exit as shown in the following
table:
┌──────────────────────────────────────────────────────────────────────┐
│ Error Special Built-in Other Utilities │
├──────────────────────────────────────────────────────────────────────┤
│Shell language syntax error exits exits │
│Utility syntax error (option or exits does not exit │
│operand error) │
│Redirection error exits does not exit │
│Variable assignment error exits does not exit │
│Expansion error exits exits │
│Command not found n/a might exit │
│Dot script not found exits n/a │
└──────────────────────────────────────────────────────────────────────┘
An expansion error is one that occurs when the shell expansions are
carried out (for example, ${x!y}, because ! is not a valid operator).
An implementation can treat these as syntax errors if it is able to
detect them during tokenization, rather than during expansion.
If any of the errors shown as "might exit" or "exits" occur in a sub‐
shell, the subshell exits or might exit with a non-zero status, but the
script containing the subshell does not exit because of the error.
In all of the cases shown in the table, an interactive shell writes a
diagnostic message to standard error without exiting.
USAGE
See largefile(5) for the description of the behavior of ksh and rksh
when encountering files greater than or equal to 2 Gbyte (2^31 bytes).
EXIT STATUS
Each command has an exit status that can influence the behavior of
other shell commands. The exit status of commands that are not utili‐
ties is documented in this section. The exit status of the standard
utilities is documented in their respective sections.
If a command is not found, the exit status is 127. If the command name
is found, but it is not an executable utility, the exit status is 126.
Applications that invoke utilities without using the shell should use
these exit status values to report similar errors.
If a command fails during word expansion or redirection, its exit sta‐
tus is greater than zero.
When reporting the exit status with the special parameter ?, the shell
reports the full eight bits of exit status available. The exit status
of a command that terminated because it received a signal reported as
greater than 128.
FILES
/etc/profile
/etc/suid_profile
$HOME/.profile
/tmp/sh*
/dev/null
ATTRIBUTES
See attributes(5) for descriptions of the following attributes:
/usr/bin/ksh, /usr/bin/rksh
┌─────────────────────────────┬─────────────────────────────┐
│ ATTRIBUTE TYPE │ ATTRIBUTE VALUE │
├─────────────────────────────┼─────────────────────────────┤
│Availability │SUNWcsu │
├─────────────────────────────┼─────────────────────────────┤
│CSI │Enabled │
└─────────────────────────────┴─────────────────────────────┘
/usr/xpg4/bin/sh
┌─────────────────────────────┬─────────────────────────────┐
│ ATTRIBUTE TYPE │ ATTRIBUTE VALUE │
├─────────────────────────────┼─────────────────────────────┤
│Availability │SUNWxcu4 │
├─────────────────────────────┼─────────────────────────────┤
│CSI │Enabled │
├─────────────────────────────┼─────────────────────────────┤
│Interface Stability │Standard │
└─────────────────────────────┴─────────────────────────────┘
SEE ALSOcat(1), cd(1), chmod(1), cut(1), echo(1), env(1), getoptcvt(1),
jobs(1), login(1), newgrp(1), paste(1), pfksh(1), pfexec(1), ps(1),
shell_builtins(1), stty(1), test(1), vi(1), dup(2), exec(2), fork(2),
ioctl(2), lseek(2), pipe(2), ulimit(2), umask(2), rand(3C), signal(3C),
signal.h(3HEAD), wait(3C), a.out(4), profile(4), attributes(5), envi‐
ron(5), largefile(5), standards(5)
Morris I. Bolsky and David G. Korn, The KornShell Command and Program‐
ming Language, Prentice Hall, 1989.
WARNINGS
The use of setuid shell scripts is strongly discouraged.
NOTES
If a command which is a tracked alias is executed, and then a command
with the same name is installed in a directory in the search path
before the directory where the original command was found, the shell
continues to exec the original command. Use the -t option of the alias
command to correct this situation.
Some very old shell scripts contain a ^ as a synonym for the pipe char‐
acter |.
Using the fc built-in command within a compound command causes the
whole command to disappear from the history file.
The built-in command .file reads the whole file before any commands are
executed. Therefore, alias and unalias commands in the file does not
apply to any functions defined in the file.
When the shell executes a shell script that attempts to execute a non-
existent command interpreter, the shell returns an erroneous diagnostic
message that the shell script file does not exist.
SunOS 5.10 29 Jun 2005 ksh(1)
