exec(3)

NAME

   execl, execlp, execle, execv, execvp, execvpe - execute a file

SYNOPSIS

   #include <unistd.h>

   extern char **environ;

   int execl(const char *path, const char *arg, ...
                   /* (char  *) NULL */);
   int execlp(const char *file, const char *arg, ...
                   /* (char  *) NULL */);
   int execle(const char *path, const char *arg, ...
                   /*, (char *) NULL, char * const envp[] */);
   int execv(const char *path, char *const argv[]);
   int execvp(const char *file, char *const argv[]);
   int execvpe(const char *file, char *const argv[],
                   char *const envp[]);

   Feature Test Macro Requirements for glibc (see feature_test_macros(7)):

   execvpe(): _GNU_SOURCE

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 name of a file that  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(), execvp(), and execvpe()  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() and execvpe() functions allow the caller  to  specify  the
   environment  of  the  executed program via the argument envp.  The envp
   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
   calling process.

   Special semantics for execlp() and execvp()
   The  execlp(),  execvp(), and execvpe() functions duplicate the actions
   of the shell in searching for  an  executable  file  if  the  specified
   filename does not contain a slash (/) character.  The file is sought in
   the colon-separated list of directory pathnames specified in  the  PATH
   environment  variable.   If  this variable isn't defined, the path list
   defaults to the current directory followed by the list  of  directories
   returned by confstr(_CS_PATH).  (This confstr(3) call typically returns
   the value "/bin:/usr/bin".)

   If the specified filename includes a  slash  character,  then  PATH  is
   ignored, and the file at the specified pathname is executed.

   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

   The  exec() functions return only if an error has occurred.  The return
   value is -1, and errno is set to indicate the error.

ERRORS

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

VERSIONS

   The execvpe() function first appeared in glibc 2.11.

ATTRIBUTES

   For   an   explanation   of   the  terms  used  in  this  section,  see
   attributes(7).

   
   Interface                      Attribute      Value       
   
   execl(), execle(), execv()     Thread safety  MT-Safe     
   
   execlp(), execvp(), execvpe()  Thread safety  MT-Safe env 
   

CONFORMING TO

   POSIX.1-2001, POSIX.1-2008.

   The execvpe() function is a GNU extension.

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),   execveat(2),   fork(2),   ptrace(2),  fexecve(3),
   system(3), environ(7)

COLOPHON

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   description  of  the project, information about reporting bugs, and the
   latest    version    of    this    page,    can     be     found     at
   https://www.kernel.org/doc/man-pages/.

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