man pid waitpid

pid(n)                       Tcl Built-In Commands                      pid(n)

______________________________________________________________________________

NAME
       pid - Retrieve process id(s)

SYNOPSIS
       pid ?fileId?
_________________________________________________________________

DESCRIPTION
       If  the  fileId  argument  is  given then it should normally refer to a
       process pipeline created with the open command.  In this case  the  pid
       command  will  return a list whose elements are the process identifiers
       of all the processes in the pipeline, in order.  The list will be empty
       if  fileId refers to an open file that isn't a process pipeline.  If no
       fileId argument is given then pid returns the process identifier of the
       current  process.   All  process  identifiers  are  returned as decimal
       strings.

KEYWORDS
       file, pipeline, process identifier

Tcl                                   7.0                               pid(n)
FORK(3am)                  GNU Awk Extension Modules                 FORK(3am)

NAME
       fork, wait, waitpid - basic process management

SYNOPSIS
       @load "fork"

       pid = fork()

       ret = waitpid(pid)

       ret = wait();

DESCRIPTION
       The fork extension adds three functions, as follows.

       fork() This  function  creates  a  new process. The return value is the
              zero in the child and the process-id number of the child in  the
              parent,  or  -1  upon error. In the latter case, ERRNO indicates
              the problem.  In the child, PROCINFO["pid"] and PROCINFO["ppid"]
              are updated to reflect the correct values.

       waitpid()
              This  function takes a numeric argument, which is the process-id
              to wait for. The return value is that of the  waitpid(2)  system
              call.

       wait() This  function  waits  for  the  first child to die.  The return
              value is that of the wait(2) system call.

BUGS
       There is no corresponding exec() function.

       The interfaces could be enhanced to provide more facilities,  including
       pulling out the various bits of the return status.

EXAMPLE
       @load "fork"
       ...
       if ((pid = fork()) == 0)
           print "hello from the child"
       else
           print "hello from the parent"

SEE ALSO
       GAWK:  Effective  AWK  Programming,  filefuncs(3am),  fnmatch(3am), in-
       place(3am), ordchr(3am), readdir(3am),  readfile(3am),  revoutput(3am),
       rwarray(3am), time(3am).

       fork(2), wait(2), waitpid(2).

AUTHOR
       Arnold Robbins, arnold@skeeve.com.

COPYING PERMISSIONS
       Copyright (C) 2012, 2013, 2018, Free Software Foundation, Inc.

       Permission  is  granted  to make and distribute verbatim copies of this
       manual page provided the copyright notice and  this  permission  notice
       are preserved on all copies.

       Permission  is granted to copy and distribute modified versions of this
       manual page under the conditions for verbatim  copying,  provided  that
       the  entire  resulting derived work is distributed under the terms of a
       permission notice identical to this one.

       Permission is granted to copy and distribute translations of this  man-
       ual page into another language, under the above conditions for modified
       versions, except that this permission notice may be stated in a  trans-
       lation approved by the Foundation.

Free Software Foundation          Feb 02 2018                        FORK(3am)