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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).
       ┌───────────────────────────────┬───────────────┬─────────────┐
       │ InterfaceAttributeValue       │
       ├───────────────────────────────┼───────────────┼─────────────┤
       │ 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

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       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)