NAME

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

LIBRARY

       Standard C library (libc, -lc)

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 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
       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  new process image 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.

       execvpe() searches for the program using the value of PATH from the caller's  environment,
       not from the envp argument.

       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 │
       └───────────────────────────────────────────────────────────┴───────────────┴─────────────┘

STANDARDS

       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)