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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 pro-
       cess 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 argu-
       ments must be terminated by a NULL pointer, and, since  these  are  variadic  func-
       tions, 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 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 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 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 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  "cur-
       rent 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)

COLOPHON
       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.ker-
       nel.org/doc/man-pages/.



GNU                               2009-02-22                           EXEC(3)

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