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

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

       #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[]);

       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	 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-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() 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 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() function also specifies the environment  of	 the  executed
       process by following the NULL pointer that terminates the list of argu‐
       ments in the argument list or the pointer to the	 argv  array  with  an
       additional  argument.  This additional 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 current process.

   Special semantics for execlp() and execvp()
       The functions execlp() and execvp() will duplicate the actions  of  the
       shell  in  searching  for  an executable file if the specified filename
       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	 addi‐
       tion, 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.)

       If  any	of  the exec() functions returns, an error will have occurred.
       The return value is -1, and errno will be set to indicate the error.

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


       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.

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

       This  page  is  part of release 3.22 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				  2009-02-22			       EXEC(3)

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