Persistent perl

[njcodewarrior]

I've written a script that monitors a number of directories for changes in file modification times. It goes something like this:

#! /usr/bin/perl

use strict;
use warnings;

my @directories = qw{/foo /bar};
my $directory;
my @files;

while ( 1 ) {
    
    FILECHECK:
    foreach $directory ( @directories ) {
        
        @files = glob("${directory}/*.log");
        next FILECHECK unless @files;

        do some stuff here...
    }

    sleep 30;

}

Obviously, the script runs indefinitely and I need to keep it running after I logout of my shell. With shell scripts, I typically use nohup and put the pid in the background (&), but I was wondering if there are any other ways to do it?

[borisz]

Detach your script from the terminal. Make it a daemon. Perhaps with Proc::Daemon.

[Argel]

Sounds like you want to make it a daemon:

use IO::Socket;
use POSIX qw(WNOHANG setsid);

sub daemonize {
        $SIG{CHLD} = 'IGNORE';        # Configure to autoreap zombies
        die "Can't fork" unless defined ( my $child = fork );  # FORK 
+<<<<<<<<<<<<
        CORE::exit(0) if $child;      # Parent exits
        setsid();                     # Become session leader
        open( STDIN,  "</dev/null" ); # Detach STDIN from shell
        open( STDOUT, ">/dev/null" ); # Detach STDOUT from shell
        open( STDERR, ">&STDOUT"   ); # Detach STDERR from shell
        chdir '/tmp';                 # Change working directory
        umask(0);                     # Reset umask
        $ENV{PATH} = '/bin:/sbin:/usr/sbin';  # Reset PATH
        }

Note: Verify your system supports autoreapping of zombies.

You can read more in this thread.

[njcodewarrior]

Do I have to be the superuser/sysadmin to run the daemon?

[Argel]

The code doesn't do anything special that other programs do not do for other reasons. Common things like manipulating filehandles, changing environment variables, and forking. There are no daemons under UNIX in the stict sense. It's just a concept, a term used to set expectations for the reader. So to answer your question any user can do it (though, other aspects of your program may require root).

[CountZero]

Perhaps run the script as a cron-job?

[roboticus]

njcodewarrior--

Assuming your system uses it, you could create an inittab entry for your job. Then when you start the system to the appropriate runlevel, it will just run for you.

--roboticus

[bowei_99]

It seems from your post that you're on a *nix platform, in which case you could also create a startup script in /etc/init.d/ to launch the process each time it boots. An earlier post to include it in /etc/inittab will also only be launched when it hits a given runlevel, e.g. at boot time.

[asz]

here's another way to do it: Guide to a happier unix life - screen

1. start a screen named "dirmonitor"

   bash$ screen -S dirmonitor

2. you are now inside screen; start your program

   bash$ ./dirmonitor.pl

3. press CTRL-a d to detache the screen (your program now runs in the background inside screen)

4. reattach the screen named "dirmonitor"

   bash$ screen -r dirmonitor
:)))))

[davorg]

There's alway PPerl.