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
       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 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-
       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.

   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
       variable 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
       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.)

       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
       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 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.

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

COLOPHON
       This page is part of release 5.04 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)