use strict;
use warnings;

my $fileContent = <<DATA;
abc:AB CD:100
def:DE FG:101
ghi:GH IJ:102
abc:AB CD:100
ghi:GH IJ:103
DATA

open FILE, '<', \$fileContent;

while (<FILE>) {
    chomp; # chomp not chop. $_ is default so omit
    my @elements = split /:/, $_;

    next unless $elements[0] eq 'abc';
    print "Matched: ", join ('|', @elements), "\n";
}

close FILE;