Hi, try wrapping $fh with the <> operator. Otherwise, you just keep setting $line to the $fh object, until you run out of resources. 
# wrong
while (my $line = $fh){

# right
while (my $line = <$fh >){

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Additionally, unless you need to process each line individually, it might be simpler to write 
open (my $fh, "<", "test.txt");
my @file_array = (<$fh>);
print @file_array,"\n";

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P.S. Since you are dealing with big files, you might want to use ARGV's special line by line processing magic. That way, you never pull the whole file into memory. Google for perl ARGV magic. 

#!/usr/bin/perl
use warnings;
use strict;

# use ARGV's magic
@ARGV = "test.txt";

my @results;

while ( <ARGV> ){
   chomp $_;
    if ($_ =~ m/head/){
        push (@results, $_);
      }
}

print "@results\n";

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I'm not really a human, but I play one on earth.
Old Perl Programmer Haiku ................... flash japh

In reply to Re^2: Out of Memory in Perl by zentara
in thread Out of Memory in Perl by maheshkumar

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