NAME
execvp, execvpe,
execlp —
execute a file with an optional path
search
SYNOPSIS
#include
<unistd.h>
extern char **environ;
int
execvp(const
char *file, char *const
argv[]);
int
execvpe(const
char *file, char *const
argv[], char *const
envp[]);
int
execlp(const
char *file, const char
*arg, ...);
DESCRIPTION
This family of functions replace the current process image with a new process image. The functions described in this manual page are front-ends for the execve(2) system call; see that manual page for detailed information about the replacement of the current process.
The const char *arg and
subsequent ellipses in the
execlp()
function can be thought of as arg0,
arg1, ..., argn. Together they
describe a list of one or more pointers to NUL-terminated strings that
represent the argument list available to the executed program. The first
argument, by convention, should point to the file name associated with the
file being executed. The list of arguments must be
terminated by a null pointer.
The
execvp() and
execvpe() functions provide an array of pointers to
NUL-terminated strings that represent the argument list available to the new
program. The first argument, by convention, should point to the file name
associated with the file being executed. The array of pointers
must be terminated by a null pointer itself.
The
execvpe()
function also specifies the environment of the executed process by following
the pointer to the argv array with an additional
parameter. This additional parameter is an array of pointers to
NUL-terminated strings and must be terminated by a null
pointer itself. The other functions take the environment for the new process
image from the external variable environ in the
current process.
These functions have special semantics.
The functions
execlp(),
execvp() and execvpe() 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
PATH variable. If this variable isn't specified,
_PATH_DEFPATH from
<paths.h> is used instead,
its value being:
/usr/bin:/bin:/usr/sbin:/sbin:/usr/X11R6/bin:/usr/local/bin:/usr/local/sbin
In addition, certain errors are treated specially.
If permission is denied for a file (the attempted
execve(2)
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(2)
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 these functions return, an error has occurred. The return value is -1, and the global variable errno will be set to indicate the error.
FILES
- /bin/sh
- default shell program
ERRORS
execvp(),
execvpe(), and execlp() may
fail and set errno for any of the errors specified for
the library functions execve(2) and
malloc(3).
SEE ALSO
sh(1), execve(2), fork(2), ktrace(2), ptrace(2), execv(3), environ(7)
STANDARDS
Historically, the default path for the
execvp() and execlp()
functions was
.:/bin:/usr/bin.
This was changed to improve security and behaviour.
The behavior of execvp() and
execlp() 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.
Traditionally, the functions execvp() and
execlp() 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.
execvp() and
execlp() conform to IEEE Std
1003.1-1988 (“POSIX.1”).
execvpe() is a GNU extension.
HISTORY
A predecessor to execvp(),
pexec(), first appeared in the Programmer's
Workbench (PWB/UNIX). The functions execvp() and
execlp() first appeared in
Version 7 AT&T UNIX.