oracular (3) exec.3.gz

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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).

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

VERSIONS

       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.

STANDARDS

       environ
       execl()
       execlp()
       execle()
       execv()
       execvp()
              POSIX.1-2008.

       execvpe()
              GNU.

HISTORY

       environ
       execl()
       execlp()
       execle()
       execv()
       execvp()
              POSIX.1-2001.

       execvpe()
              glibc 2.11.

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)