Hello sp4rperl, and welcome to the Monastery!

To elaborate a little on tybalt89’s answer: By declaring $endTime with my, you make it a lexical variable whose scope is limited to the enclosing block. So when the print statement is reached, $endTime no longer refers to that lexical variable, but rather to an (undeclared) package global of the same name. If you begin your script with:

use strict;
[download]

then Perl will give you an error message describing the problem. It’s also a very good idea to add:

use warnings;
[download]

to the top of every script. Note also that the /g modifiers on your regular expressions do nothing useful (Update: thanks to AnomalousMonk for the correction below), as in each case you’re looking for a single match only. And you need only one regular expression for the endTime match:

use strict;
use warnings;

my $timeLimit = '<timeLimit endTime="2016-12-28T23:59:59" startTime="2
+016-09-30T00:00:00"></timeLimit>'; 
my ($startTime) = $timeLimit =~ /startTime="(.*?)"/;
chomp($startTime);

if (my ($endTime) = $timeLimit =~ /endTime="(.*?)"/) 
{
    chomp($endTime); 
    print "[$startTime],[$endTime]\n";
}
else
{
    print "[$startTime]\n";
}
[download]

(I’m assuming that chomp($timeLimit); is a mistake for chomp($startTime);.)

Hope that helps,