Question

I am trying to run a background process in perl. I create a child process, which is used to call another perl script. I want to run few lines of code parallely with this child process. And after the child process is done.I want to print a line of code.

Main script

#!/usr/bin/perl

$|=1;

print "before the child process\n";

my $pid = fork();

if (defined $pid)
{
    system("perl testing.pl");
}

print "before wait command\n";

wait();

print "after 20 secs of waiting\n";

testing.pl

#!/usr/bin/perl

print "inside testing\n";

sleep(20);

Expected output

before the child process
before wait command
(should wait for 20 secs and then print)
after 20 secs of waiting

Answer 1

There are many problems with your script. Always:

use strict;
use warnings;

localising special variables is a good practice. Only a variable containing the special value undef returns false for defined. So, every other value (even a 0; which is the case here) returns true for defined. In the other script, the shebang is wrong.

#!/usr/bin/perl

use strict;
use warnings;

local $| = 1;

print "Before the child process\n";

unless (fork) {
    system("perl testing.pl");
    exit;
}

print "Before wait command\n";
wait;
print "After 20 secs of waiting\n";