EXEC(3)                   Linux Programmer's Manual                  EXEC(3)

NAME         top

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

SYNOPSIS         top

       #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         top

       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(), execvp(), and execvpe()
       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         top

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

ERRORS         top

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

VERSIONS         top

       The execvpe() function first appeared in glibc 2.11.

ATTRIBUTES         top

       For an explanation of the terms used in this section, see

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

CONFORMING TO         top

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

       The execvpe() function is a GNU extension.

NOTES         top

       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

       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         top

       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.

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

SEE ALSO         top

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

COLOPHON         top

       This page is part of release 5.01 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

GNU                              2019-03-06                          EXEC(3)

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