NAME
execl, execlp, execle, execv, execvp - execute a file
SYNOPSIS
#include <unistd.h>
extern char **environ;
int execl( const char *path, const char *arg, ...);
int execlp( const char *file, const char *arg, ...);
int execle( const char *path, const char *arg , ..., char *
const envp[]);
int execv( const char *path, char *const argv[]);
int execvp( const char *file, char *const argv[]);
DESCRIPTION
The exec family of functions replaces the current process
image with a new process image. The functions described in
this manual page are front-ends for the function execve(2).
(See the manual page for execve for detailed information
about the replacement of the current process.)
The initial argument for these functions is the pathname of
a file which is to be executed.
The const char *arg and subsequent ellipses in the execl,
execlp, and execle functions can be thought of as arg0,
arg1, ..., argn. Together they describe a list of one or
more pointers to null-terminated strings that represent the
argument list available to the executed program. The first
argument, by convention, should point to the file name asso-
ciated with the file being executed. The list of arguments
must be terminated by a NULL pointer.
The execv and execvp functions provide an array of pointers
to null-terminated strings that represent the argument list
available to the new program. The first argument, by con-
vention, should point to the file name associated with the
file begin executed. The array of pointers must be ter-
minated by a NULL pointer.
The execle function also specifies the environment of the
executed process by following the NULL pointer that ter-
minates the list of arguments in the parameter list or the
pointer to the argv array with an additional parameter.
This additional parameter is an array of pointers to null-
terminated strings and must be terminated by a NULL pointer.
The other functions take the environment for the new process
image from the external variable environ in the current pro-
cess.
Some of these functions have special semantics.
The functions execlp and execvp will duplicate the actions
of the shell in searching for an executable file if the
specified file name does not contain a slash (/) character.
The search path is the path specified in the environment by
the PATH variable. If this variable isn't specified, the
default path ``:/bin:/usr/bin'' is used. In addition, cer-
tain errors are treated specially.
If permission is denied for a file (the attempted execve
returned EACCES), these functions will continue searching
the rest of the search path. If no other file is found,
however, they will return with the global variable errno set
to EACCES.
If the header of a file isn't recognized (the attempted
execve returned ENOEXEC), these functions will execute the
shell with the path of the file as its first argument. (If
this attempt fails, no further searching is done.)
RETURN VALUES
If any of the exec functions returns, an error will have
occurred. The return value is -1, and the global variable
errno will be set to indicate the error.
FILES
/bin/sh
ERRORS
All of these functions may fail and set errno for any of the
errors specified for the library function execve(2).
SEE ALSO
sh(1), execve(2), fork(2), environ(5), ptrace(2)
COMPATIBILITY
On some other systems the default PATH has the current work-
ing directory listed after /bin and /usr/bin, as an anti-
Trojan-horse measure. As of libc 5.4.7, Linux still uses the
traditional "current directory first" default PATH.
The behavior of execlp and execvp when errors occur while
attempting to execute the file is historic practice, but has
not traditionally been documented and is not specified by
the POSIX standard. BSD (and possibly other systems) do an
automatic sleep and retry if ETXTBSY is encountered. Linux
treats it as a hard error and returns immediately.
Traditionally, the functions execlp and execvp ignored all
errors except for the ones described above and ENOMEM and
E2BIG, upon which they returned. They now return if any
error other than the ones described above occurs.
STANDARDS
Execl, execv, execle, execlp and execvp conform to IEEE
Std1003.1-88 (``POSIX.1'').