execl(3)execl(3)Name
execl, execv, execle, execlp, execvp, exect, environ - execute a file
Syntax
execl(name, arg0, arg1, ..., argn, (char *)0)
char *name, *arg0, *arg1, ..., *argn;
execv(name, argv)
char *name, *argv[];
execle(name, arg0, arg1, ..., argn, (char *)0, envp)
char *name, *arg0, *arg1, ..., *argn, *envp[];
execlp(file, arg0, arg1, ..., argn, (char *)0)
char *file, *arg0, *arg1, ..., *argn;
execvp(file,argv)
char *file, *argv[];
exect(name, argv, envp)
char *name, *argv[], *envp[];
extern char **environ;
Description
These routines provide various interfaces to the system call. Refer to
for a description of their properties; only brief descriptions are pro‐
vided here.
In all their forms, these calls overlay the calling process with the
named file, then transfer to the entry point of the core image of the
file. There can be no return from a successful exec. The calling core
image is lost.
The name argument is a pointer to the name of the file to be executed.
The pointers arg[0], arg[1] ... address null-terminated strings. Con‐
ventionally arg[0] is the name of the file.
Two interfaces are available. is useful when a known file with known
arguments is being called; the arguments to are the character strings
constituting the file and the arguments; the first argument is conven‐
tionally the same as the file name (or its last component). A 0 argu‐
ment must end the argument list.
The version is useful when the number of arguments is unknown in
advance. The arguments to are the name of the file to be executed and
a vector of strings containing the arguments. The last argument string
must be followed by a 0 pointer.
The version is used when the executed file is to be manipulated with
The program is forced to single step a single instruction giving the
parent an opportunity to manipulate its state. On the VAX-11 this is
done by setting the trace bit in the process status longword.
When a C program is executed, it is called as follows:
main(argc, argv, envp)
int argc;
char **argv, **envp;
where argc is the argument count and argv is an array of character
pointers to the arguments themselves. As indicated, argc is conven‐
tionally at least one and the first member of the array points to a
string containing the name of the file.
The argv is directly usable in another because argv[argc] is 0.
The envp is a pointer to an array of strings that constitute the envi‐
ronment of the process. Each string consists of a name, an “=”, and a
null-terminated value. The array of pointers is terminated by a null
pointer. The shell passes an environment entry for each global shell
variable defined when the program is called. See for some convention‐
ally used names. The C run-time start-off routine places a copy of
envp in the global cell which is used by and to pass the environment to
any subprograms executed by the current program.
The and routines are called with the same arguments as and but dupli‐
cate the shell's actions in searching for an executable file in a list
of directories. The directory list is obtained from the environment.
Restrictions
If is called to execute a file that turns out to be a shell command
file, and if it is impossible to execute the shell, the values of
argv[0] and argv[-1] will be modified before return.
The function receives a SIGILL error if passed a PATH list that con‐
tains names greater than NAME_MAX (255) characters long.
Diagnostics
If the file cannot be found, if it is not executable, if it does not
start with a valid magic number, if maximum memory is exceeded, or if
the arguments require too much space, a return constitutes the diagnos‐
tic; the return value is -1. For further information, see Even for the
super-user, at least one of the execute-permission bits must be set for
a file to be executed.
Files
Shell, invoked if command file found
by or
See Alsocsh(1), execve(2), fork(2), environ(7)
VAX execl(3)
