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'
);
#After processing, I should get:
#'string that I need to gather the common base from: number '
my $string = '';

my ($match_string, @rest_strings) = @strings;
for my $string_idx (0..length($match_string)){
 if(scalar(@rest_strings) > (grep { substr($match_string, $string_idx, 1) eq substr($_, $string_idx, 1) } @rest_strings)){
  $string = substr($match_string, 0, $string_idx);
  last;
 }
}