If the line numbers are always at the start of the line and you just wanted to pull out certain ones, you could say

while ( <FILE> ) {
   print if ( /^(1|3|4)/ );
}
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If the line is always a number followed by "perlmonks(stuff)" and you just want to grab the stuff, you could say

while ( <FILE> ) {
   if ( /^(1|3|4) perlmonks\(([^\)])\)/ ) {
      print "$2\n";
   }
}
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Is that the checking you wanted to do? If not, you need to describe what you want to be doing a bit better. Anyways, hope that helps.