my %keymap = %{$_[0]};

##</code><code>##

  my $file_name = shift;
  my $hr = shift;

##</code><code>##

  ...
  $hr->{$2} = $1;

##</code><code>##

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

my $ALWAYS_USE_REF = 1;

main( @ARGV );
exit 0;

sub main {
    my %hash;
    recursively_foo_my_hash( \%hash, 5 );
    print_hash_ref_contents( \%hash );

    return 1;
}

sub recursively_foo_my_hash {
    my $hr = shift;

    print "RFMH called with hash ref: $hr\n";
    
    my %new_hash = %{ $hr };
    my $depth = shift;

    $hr = \%new_hash unless $ALWAYS_USE_REF;
    
    return 1 unless $depth > 0;
    $hr->{"foo_$depth"} = rand();	# Add some data
    recursively_foo_my_hash( $hr, $depth - 1 );
    return 1;
}

sub print_hash_ref_contents {
    my $hr = shift;
    print "Hash ref [$hr] contains:\n";
    foreach my $k ( sort keys %$hr ) {
	print "$k -> $hr->{$k}\n";
    }
    return 1;
}