exec(3)



EXEC(3)                    Linux Programmer's Manual                   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 fur-
       ther 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.  To-
       gether  they describe a list of one or more pointers to null-terminated
       strings that represent the argument list available to the executed pro-
       gram.   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 file-
       name does not contain a slash (/) character.  The file is sought in the
       colon-separated list of directory pathnames specified in the PATH envi-
       ronment  variable.   If  this variable isn't defined, the path list de-
       faults to a list  that  includes  the  directories  returned  by  conf-
       str(_CS_PATH)  (which  typically returns the value "/bin:/usr/bin") and
       possibly also the current working directory; see NOTES for further  de-
       tails.

       If  the specified filename includes a slash character, then PATH is ig-
       nored, 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  at-
       tributes(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
       The default search path (used when the environment does not contain the
       variable PATH) shows some variation across systems.  It  generally  in-
       cludes  /bin and /usr/bin (in that order) and may also include the cur-
       rent 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 attempt-
       ing 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 de-
       scribed 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 re-
       quirements of POSIX.1.  This was fixed in glibc 2.24.

SEE ALSO
       sh(1), execve(2), execveat(2),  fork(2),  ptrace(2),  fexecve(3),  sys-
       tem(3), environ(7)

COLOPHON
       This  page  is  part of release 4.16 of the Linux man-pages project.  A
       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/.

GNU                               2017-09-15                           EXEC(3)

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