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



NAME
       execl, execlp, execle, execv, execvp - execute a file(1,n)

SYNOPSIS
       #include <unistd.h>

       extern char **environ;

       int execl(const char *path, const char *arg, ...);
       int execlp(const char *file(1,n), 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(1,n), char *const argv[]);

DESCRIPTION
       The exec(3,n,1 builtins) family of functions replaces the current process image with  a
       new  process  image.   The  functions described in(1,8) 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(1,n)
       which is to be executed.

       The  const  char *arg and subsequent ellipses in(1,8) 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(1,n) name asso-
       ciated with the file(1,n) 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
       file(1,n) name associated with the file(1,n) being executed.  The array of point-
       ers 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(1,8) the parameter list or the pointer to the argv  array  with  an
       additional  parameter.  This additional parameter is an array of point-
       ers 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(1,8) the current process.

       Some of these functions have special semantics.

       The functions execlp and execvp will duplicate the actions of the shell
       in(1,8) searching for an executable file(1,n) if(3,n) the specified file(1,n) name does not
       contain a slash (/) character.  The search path is the  path  specified
       in(1,8) the environment by the PATH variable.  If this variable isn't speci-
       fied, the default path ``:/bin:/usr/bin'' is used.  In  addition,  cer-
       tain errors are treated specially.

       If  permission is denied for a file(1,n) (the attempted execve returned EAC-
       CES), these functions will continue searching the rest  of  the  search
       path.   If  no  other file(1,n) is found, however, they will return with the
       global variable errno set(7,n,1 builtins) to EACCES.

       If the header of a file(1,n) isn't recognized (the attempted execve returned
       ENOEXEC),  these  functions will execute the shell with the path of the
       file(1,n) as its first argument.  (If this attempt fails, no further search-
       ing is done.)

RETURN VALUE
       If any of the exec(3,n,1 builtins) functions returns, an error(8,n) will have occurred.  The
       return value is -1, and the global variable errno will be set(7,n,1 builtins) to  indi-
       cate the error.

FILES
       /bin/sh

ERRORS
       All  of  these  functions  may fail and set(7,n,1 builtins) errno for any of the errors
       specified for the library function execve(2).

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

COMPATIBILITY
       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(1,n) is historic practice, but has not  traditionally  been
       documented  and is not specified by the POSIX standard. BSD (and possi-
       bly other systems) do an  automatic  sleep(1,3)  and  retry  if(3,n)  ETXTBSY  is
       encountered. Linux treats it as a hard error(8,n) 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(3,n)  any  error(8,n) other than the ones
       described above occurs.

CONFORMING TO
       execl, execv, execle, execlp and execvp conform  to  IEEE  Std1003.1-88
       (``POSIX.1'').



BSD MANPAGE                       1993-11-29                           EXEC(3)

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