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

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

       #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

       The exec() family of functions replaces the current process image with a
       new process image.  The functions described in this manual page are
       layered on top of 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"

   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.

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

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

       The execvpe() function first appeared in glibc 2.11.

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

       The execvpe() function is a GNU extension.

       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.

       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

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

       This page is part of release 5.10 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                                2019-08-02                            EXEC(3)