#!/usr/bin/perl
use strict;
use warnings;
use Data::Dumper;

my %hash;
@hash{ 'a'..'d' } = ([175, 450], [0, 350], [0, 50], [300, 50]);

print "Initial hash\n";
print Dumper \%hash;


print "\nhash after call\n";
push_1(%hash);
print Dumper \%hash;


sub push_1 {
	my %hash = @_;
	for (keys %hash) {
		push @{ $hash{$_} }, 1;
	}
}
__END__
*** Output

C:\perlp>perl t.pl
Initial hash
$VAR1 = {
          'c' => [
                   0,
                   50
                 ],
          'a' => [
                   175,
                   450
                 ],
          'b' => [
                   0,
                   350
                 ],
          'd' => [
                   300,
                   50
                 ]
        };

hash after call
$VAR1 = {
          'c' => [
                   0,
                   50,
                   1
                 ],
          'a' => [
                   175,
                   450,
                   1
                 ],
          'b' => [
                   0,
                   350,
                   1
                 ],
          'd' => [
                   300,
                   50,
                   1
                 ]
        };

C:\perlp>