bionic (3) exec.3.gz

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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 a list that includes the directories returned by
       confstr(_CS_PATH) (which typically returns the value  "/bin:/usr/bin")  and  possibly  also  the  current
       working directory; see NOTES for further details.

       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).

       ┌──────────────────────────────┬───────────────┬─────────────┐
       │InterfaceAttributeValue       │
       ├──────────────────────────────┼───────────────┼─────────────┤
       │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

       The  default  search  path  (used  when  the  environment  does not contain the variable PATH) shows some
       variation across systems.  It generally includes /bin and /usr/bin (in that order) and may  also  include
       the  current  working  directory.   On some other systems, the current working is included after /bin and
       /usr/bin, as an anti-Trojan-horse measure.   The  glibc  implementation  long  followed  the  traditional
       default  where  the current working directory is included at the start of the search path.  However, some
       code refactoring during the development of glibc 2.24 caused the current working directory to be  dropped
       altogether  from  the  default  search  path.   This  accidental  behavior  change  is  considered mildly
       beneficial, and won't be reverted.

       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.

BUGS

       Before  glibc  2.24, execl() and execle() employed realloc(3) internally and were consequently not async-
       signal-safe, in violation of the requirements of POSIX.1.  This was fixed in glibc 2.24.

SEE ALSO

       sh(1), execve(2), execveat(2), fork(2), ptrace(2), fexecve(3), system(3), environ(7)

COLOPHON

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