EXEC(3) 					     Linux Programmer's Manual						   EXEC(3)



NAME
       execl, execlp, execle, execv, execvp, execvpe - execute a file

SYNOPSIS
       #include 

       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[]);
       int execvpe(const char *file, char *const argv[],
		  char *const envp[]);

   Feature Test Macro Requirements for glibc (see feature_test_macros(7)):

       execvpe(): _GNU_SOURCE

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 execve(2).  (See the manual page for execve(2) for further details about  the  replace‐
       ment of the current process image.)

       The initial argument for these functions is the name of a file that 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 argu‐
       ment  list  available  to the executed program.	The first argument, by convention, should point to the filename associated
       with the file being executed.  The list of arguments must be terminated by a NULL pointer, and, since  these  are  variadic
       functions, this pointer must be cast (char *) NULL.

       The  execv(),  execvp(), and execvpe() functions provide an array of pointers to null-terminated strings that represent the
       argument list available to the new program.  The first argument, by convention, should point  to  the  filename	associated
       with the file being executed.  The array of pointers must be terminated by a NULL pointer.

       The  execle()  and execvpe() functions allow the caller to specify the environment of the executed program via the argument
       envp.  The envp argument 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 calling process.

   Special semantics for execlp() and execvp()
       The  execlp(),  execvp(), and execvpe() functions duplicate the actions of the shell in searching for an executable file if
       the specified filename does not contain a slash (/) character.  The file is sought in the colon-separated list of directory
       pathnames  specified  in the PATH environment variable.	If this variable isn't defined, the path list defaults to the cur‐
       rent directory followed by the list of directories returned by confstr(_CS_PATH).  (This confstr(3) call typically  returns
       the value "/bin:/usr/bin".)

       If  the specified filename includes a slash character, then PATH is ignored, and the file at the specified pathname is exe‐
       cuted.

       In addition, certain errors are treated specially.

       If permission is denied for a file (the attempted execve(2) failed with the error EACCES), these  functions  will  continue
       searching the rest of the search path.  If no other file is found, however, they will return with errno set to EACCES.

       If the header of a file isn't recognized (the attempted execve(2) failed with the error ENOEXEC), these functions will exe‐
       cute the shell (/bin/sh) with the path of the file as its first argument.  (If this attempt fails, no further searching	is
       done.)

RETURN VALUE
       The  exec()  functions only return if an error has have occurred.  The return value is -1, and errno is set to indicate the
       error.

ERRORS
       All of these functions may fail and set errno for any of the errors specified for execve(2).

VERSIONS
       The execvpe() function first appeared in glibc 2.11.

CONFORMING TO
       POSIX.1-2001, POSIX.1-2008.

       The execvpe() function is a GNU extension.

NOTES
       On some other systems, the default path (used when the environment does not contain the	variable  PATH)  has  the  current
       working	directory  listed after /bin and /usr/bin, as an anti-Trojan-horse measure.  Linux uses here the traditional "cur‐
       rent 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 auto‐
       matic 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.

SEE ALSO
       sh(1), execve(2), fork(2), ptrace(2), fexecve(3), environ(7)

COLOPHON
       This  page  is  part  of  release 3.40 of the Linux man-pages project.  A description of the project, and information about
       reporting bugs, can be found at http://www.kernel.org/doc/man-pages/.



GNU							    2010-09-25							   EXEC(3)