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

NAME
       execl, execlp, execle, execv, execvp - 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[]);

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 the function execve(2).  (See the manual page for execve(2) for detailed information
       about the replacement of the current process.)

       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-terminated strings  that  represent  the
       argument  list available to the executed program.  The first argument, by convention, should point to the filename asso-
       ciated 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()  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 termi-
       nates the list of arguments in the parameter list or the pointer to the argv array with an additional  parameter.   This
       additional  parameter  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 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 (/bin/sh) with the path of the file as its first argument.  (If this attempt fails, no further searching is done.)

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

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

CONFORMING TO
       POSIX.1-2001.

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)

GNU                                                        1993-11-29                                                   EXEC(3)