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 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  envi-
       ronment 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 con-
       fstr(_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).

       +------------------------------+---------------+-------------+
       |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
       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 con-
       sidered 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  tradition-
       ally  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

       This page is part of release 4.15 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)