Is it possible to background a perl script from within itself?

[reyjrar]

Is it possible to background a perl script from within itself, so that it starts like a daemon, i.e. like a generic equivalent of & on unix?

> ./myserver
Server starting ... bound to port 4000!

Originally posted as a Categorized Question.

[Fastolfe]

I typically use a variation of this 'daemonize' code taken from perlipc. This sets up the script's environment and disassociates it from the caller entirely.

sub daemonize {
   chdir '/'               or die "Can't chdir to /: $!";
   open STDIN, '/dev/null' or die "Can't read /dev/null: $!";
   open STDOUT, '>/dev/null'
                                       or die "Can't write to /dev/nul
+l: $!";
   defined(my $pid = fork) or die "Can't fork: $!";
   exit if $pid;
   setsid                  or die "Can't start a new session: $!";
   open STDERR, '>&STDOUT' or die "Can't dup stdout: $!";
}

You could also open STDOUT to point to, say, a log file here. Or a tied filehandle passing its data to syslog.

[japhy]

I believe this will do the trick:

#!/usr/bin/perl

print "Now backgrounding your process...\n";
fork and exit;
# rest of code goes here

[jeroenes]

See this thread for info on executing backgrounding a script.
Specialized modules exist for this kind of problem:

• Net::daemon
• Proc::daemon
I was amazed by the length of the 'detaching' sequence.
You need Net::daemon if you want to claim a socket, otherwise Proc::daemon should suffice.

[belg4mit]

FWIW "starting as a daemon" is different than the "&". The latter is a form of shell job control. Others have given examples of the former.

[hbo]

You have to setsid too, to disassociate from your parent's process group:

#!/usr/bin/perl
use strict;
use warnings;
use POSIX qw(setsid);

# Become a daemon
my $pid=fork;
exit if $pid; # Parent exits here
die "Couldn't fork $!" unless defined($pid);
die "Couldn't start new session $!" unless POSIX::setsid();

# Do your daemon bit...

[hbo]

OK, rereading the text at the top..

One way to achieve the result is to resort to bash:

#!/bin/bash
perlprog.pl&

But it seems silly just to avoid typing '&'. What exactly are you trying to achieve?

[Improv]

One solution is to fork and have the parent exit.

[merlyn]

Yes. You can find the answer by looking in the FAQ, or by looking at perlman:perlipc.

Originally posted as a Categorized Answer.

[jettero]

Re: Is it possible to background a perl script from within itself?

Originally posted as a Categorized Answer.

[Anonymous Monk]

REAT'

Originally posted as a Categorized Answer.