EXEC(3)                   (2019-08-02)                    EXEC(3)

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

          #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

          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" 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 rep-
          resent the argument list available to the executed program.
          The first argument, by convention, should point to the file-
          name 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

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          (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 con-
          vention, should point to the filename associated with the
          file being executed.  The array of pointers must be termi-
          nated 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

          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 abso-
          lute) pathname that identifies the program to be executed.

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

          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).  allbox; lbw29 lb lb l l l.
          Interface Attribute Value T{ execl(), execle(), execv()
          T}   Thread safety  MT-Safe T{ execlp(), execvp(), execvpe()
          T}   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 sys-
          tems.  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 speci-
          fied by the POSIX standard.  BSD (and possibly other sys-
          tems) do an automatic sleep and retry if ETXTBSY is encoun-
          tered.  Linux treats it as a hard error and returns immedi-

          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.

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          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 compati-
          bility with SunOS.  This function is not employed by the
          execv() wrapper function on those architectures.

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

          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 https://www.kernel.org/doc/man-pages/.

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