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, ...
		       /* (char	 *) NULL */);
       int execlp(const char *file, const char *arg, ...
		       /* (char	 *) NULL */);
       int execle(const char *path, const char *arg, ...
		       /*, (char *) NULL, 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 fur-
       ther 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() functions can be thought of	 as  arg0,  arg1,  ...,	 argn.
       Together	 they  describe	 a list of one or more pointers to null-termi-
       nated strings that represent the argument list available	 to  the  exe-
       cuted  program.	The first argument, by convention, should point to the
       filename associated with the file being executed.  The  list  of	 argu-
       ments  must be terminated by a null pointer, and, since these are vari-
       adic 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 file-
       name does not contain a slash (/) character.  The file is sought in the
       colon-separated list of directory pathnames specified in the PATH envi-
       ronment	variable.   If	this  variable	isn't  defined,	 the path list
       defaults to the current 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 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.

ATTRIBUTES
       For   an	  explanation	of   the  terms	 used  in  this	 section,  see
       attributes(7).

       +------------------------------+---------------+-------------+
       |Interface		      | Attribute     | Value	    |
       +------------------------------+---------------+-------------+
       |execl(), execle(), execv()    | Thread safety | MT-Safe	    |
       +------------------------------+---------------+-------------+
       |execlp(), execvp(), execvpe() | Thread safety | MT-Safe env |
       +------------------------------+---------------+-------------+
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 attempt-
       ing 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.

BUGS
       Before glibc 2.24, execl() and execle() employed realloc(3)  internally
       and  were  consequently	not  async-signal-safe,	 in  violation	of the
       requirements of POSIX.1.	 This was fixed in glibc 2.24.

SEE ALSO
       sh(1), execve(2), execveat(2),  fork(2),	 ptrace(2),  fexecve(3),  sys-
       tem(3), environ(7)

COLOPHON
       This  page  is  part of release 4.10 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
       https://www.kernel.org/doc/man-pages/.



GNU				  2017-03-13			       EXEC(3)