>perl -wMstrict -le
"use List::Util qw(reduce);
 ;;
 my @ra = qw(ABCDxyz  ABCfoo  ABCDEbar);
 ;;
 use vars qw($a $b);
 my $min_start_seq =
   reduce { length($a) < length($b) ? $a : $b }
   map m{ \A \x00* }xmsg,
   map $ra[0] ^ $_,
   @ra
   ;
 my $common_starting_substring = $ra[0] & ~$min_start_seq;
 print qq{'$common_starting_substring'};
"
'ABC'