_data.txt_
abc:AB CD:100
def:DE FG:101
ghi:GH IJ:102
abc:AB CD:100
ghi:GH IJ:103

my $count;
while ( <FILE> ) {
    print if /^abc:/;
    $count++ if /^abc/;
}
print "Matched $count times\n";

_output_
abc:AB CD:100
abc:AB CD:100
Matched 2 times