exec

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 *pathname, const char *arg, ...
                       /* (char  *) NULL */);
       int execlp(const char *file, const char *arg, ...
                       /* (char  *) NULL */);
       int execle(const char *pathname, const char *arg, ...
                       /*, (char *) NULL, char *const envp[] */);
       int execv(const char *pathname, 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  functions can be grouped based on the letters following the "exec"
       prefix.

   l - execl(), execlp(), execle()
       The const char *arg and subsequent ellipses 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.

       By contrast with the 'l' functions, the 'v' functions  (below)  specify
       the command-line arguments of the executed program as a vector.

   v - execv(), execvp(), execvpe()
       The  char *const argv[] argument is an array of pointers to null-termi-
       nated strings that represent the argument list  available  to  the  new
       program.   The first argument, by convention, should point to the file-
       name associated with the file being executed.  The  array  of  pointers
       must be terminated by a null pointer.

   e - execle(), execvpe()
       The  environment of the caller is specified via the argument envp.  The
       envp argument is an array of pointers to  null-terminated  strings  and
       must be terminated by a null pointer.

       All  other  exec()  functions  (which do not include 'e' in the suffix)
       take the environment for the new process image from the external  vari-
       able environ in the calling process.

   p - execlp(), execvp(), execvpe()
       These  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 di-
       rectories 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  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.)

       All  other  exec()  functions  (which do not include 'p' in the suffix)
       take as their first argument a (relative  or  absolute)  pathname  that
       identifies the program to be executed.

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.

   Architecture-specific details
       On  sparc and sparc64, execv() is provided as a system call by the ker-
       nel (with the prototype shown  above)  for  compatibility  with  SunOS.
       This  function is not employed by the execv() wrapper function on those
       architectures.

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 5.05 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                               2019-08-02                           EXEC(3)