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



NAME
       execl, execlp, execle, execv, execvp, execvpe - 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[]);
       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 replacement 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()  func‐
       tions 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 filename associ‐
       ated 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-termi‐
       nated 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 exe‐
       cuted.  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  speci‐
       fied  in  the  PATH  environment  variable.  If this variable isn't defined, the path list
       defaults to the current directory followed by the list of directories  returned  by  conf‐
       str(_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 executed.

       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 execute 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 return only if an error has 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  "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.

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

COLOPHON
       This page is part of release 3.74 of the Linux man-pages project.  A  description  of  the
       project,  information  about  reporting  bugs, and the latest version of this page, can be
       found at http://www.kernel.org/doc/man-pages/.



GNU                                         2010-09-25                                    EXEC(3)