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

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

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 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 file
       name associated with the file being executed.  The list of
       arguments must be terminated by a NULL pointer.

       The  execv and execvp functions provide an array of point-
       ers to null-terminated strings that represent the argument
       list available to the new program.  The first argument, by
       convention, should point to the file name 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.

       Some of these functions have special semantics.

       The functions execlp and execvp will duplicate the actions
       of  the  shell  in searching for an executable file if the
       specified file name does not contain a slash  (/)  charac-
       ter.   The  search path is the path specified in the envi-
       ronment 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
       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 returned ENOEXEC), these functions will execute the
       shell with the path of the file  as  its  first  argument.
       (If this attempt fails, no further searching is done.)

RETURN VALUES
       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.

FILES
       /bin/sh

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

SEE ALSO
       sh(1), execve(2), fork(2), environ(5), ptrace(2)

COMPATIBILITY
       On some other systems the default  PATH  has  the  current
       working  directory  listed  after /bin and /usr/bin, as an
       anti-Trojan-horse measure. As of libc 5.4.7,  Linux  still
       uses  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.

STANDARDS
       Execl, execv, execle, execlp and execvp  conform  to  IEEE
       Std1003.1-88 (``POSIX.1'').

BSD MANPAGE              29 November 1993                       1