Filter a textfile to output only the lines where a given identifier is present.

filterById.pl

#!/usr/bin/perl
use strict;
my $usage = "cat input.gtf | $! idlist.txt > filtered.gtf\n";
my %ids;

my $FN_idlist = $ARGV[0];
open my $FH_idlist, "<", $FN_idlist or die $usage;


# read id list to memory
while(my $id = <$FH_idlist>){
  chomp $id;
  $ids{$id} = 1;
}


while(my $line = <STDIN>){
  my ($xloc_id) = $line =~ /(XLOC_\d+)/;
  if(defined($ids{$xloc_id})){
    print $line;
  }
}