use strict;
use warnings;


my @strings = (
    'string that I need to gather the common base from: number 1 and some other junk in it',
    'string that I need to gather the common base from: number 2 and some other junk in it',
    'string that I need to gather the common base from: number 3 and some other junk in it',
);

my $sep   = "\0";
my $nosep = "[^$sep]";
my $all   = join $sep, @strings;


$all =~ /^ ($nosep*) $nosep*? ( $sep \1 $nosep*? )+ $/x;

print "solution: '$1'";