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


       #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


       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 *)

       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 environment 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 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.)


       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


       The execvpe() function first appeared in glibc 2.11.


       For an explanation of the terms used in this section, see attributes(7).

       │InterfaceAttributeValue       │
       │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.


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


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