use strict;
use warnings;
open my $fh, "<", "somefile.txt";
while(my $line = <$fh>){
    if($line =~ /pattern/){
        print "Matched: $line";
        print $line if defined( $line = <$fh>);
        print $line if defined( $line = <$fh>);
    }
}
close($fh);