perl matching two columns from different tables -

i have table 3 columns, called table1

1       2       2       3       b 4       5       d 

i have table 1 column, called table2, looking this

a b e f 

if there match between table2 , third column of table1, want print matching line new table called output, in case should this

1    2    2    3    b 

i'm writing in perl , think should using hash. tried following

#!/usr/bin/perl use strict; use warnings;  open(my $table1,'<',"table1.txt"); open(my $table2,'<',"table2.txt"); open(my $output,'+>',"output.txt");  %hash = ();  while (<$table2>){     chomp;     $keyfield = $_;     push @{$hash{keyfield}}; } seek $table1,0,0; while (<$table1>){      chomp;      @cols = split(/\t/);      $keyfield = $cols[2];      if (exists($hash{$keyfield})) {         print $output $_, "\n";  }  } 

this approach worked before, had modify slightly. warning: useless use of push no values @ line13 (which line push is). , output empty. doing wrong?

you need use $hash{$keyfield} = 1 create association instead of push.

per tip @sobrique, can use $hash{$keyfield}++ let determine later whether key exists , give number of occurrences.