Man Pages

exec(3) - phpMan exec(3) - phpMan

Command: man perldoc info search(apropos)  


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 execve(2).  (See the manual page  for  execve(2)  for  further
       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-terminated  strings
       that  represent the argument list available to the executed program.  The first argument, by convention, should
       point to the filename associated 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
       terminates the list of arguments in the argument list or the pointer to the argv array with an additional argu-
       ment.   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 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  func-
       tions  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 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  prac-
       tice,  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)

COLOPHON
       This  page  is part of release 3.22 of the Linux man-pages project.  A description of the project, and informa-
       tion about reporting bugs, can be found at http://www.kernel.org/doc/man-pages/.



GNU                               2009-02-22                           EXEC(3)