Also, you dont need the second loop - You can make use of the fact that you are using a hash. 

use strict   ;
use warnings ;

my @data = <DATA> ;
my %freq_hash ; # What you call '%hash' 

foreach my $single_line ( @data ) { 
    chomp( $single_line ) ;
    my ( $word, $freq ) = split( / /, $single_line ) ;
    $freq_hash{ $word } = $freq ;
}

## So far all we have done is get data ## 

print "\nData Before Process:\n";

foreach my $word (sort { $freq_hash{ $b } <=> $freq_hash{ $a } } keys 
+%freq_hash ) {
    print "$word\t\t$freq_hash{$word}\n";
}

foreach my $word ( keys %freq_hash ) { 
    if( ( lc( $word ) ne $word ) and $freq_hash{ lc( $word ) } ) {
    $freq_hash{ lc( $word ) } += $freq_hash{ $word } ;
    delete( $freq_hash{ $word } ) ;
    }
}

print "\nData After Process:\n";

foreach my $word (sort { $freq_hash{ $b } <=> $freq_hash{ $a } } keys 
+%freq_hash ) {
    print "$word\t\t$freq_hash{$word}\n";
}


__DATA__
the 1
The 1
hello 15
hell 19
Hell 8

[download]

Update: Included code.

In reply to Re^2: Hash element exists/delete by tmharish
in thread Hash element exists/delete by Dr Manhattan

Title:
Use:  <p> text here (a paragraph) </p>
and:  <code> code here </code>
to format your post, it's "PerlMonks-approved HTML":


  • Posts are HTML formatted. Put <p> </p> tags around your paragraphs. Put <code> </code> tags around your code and data!
  • Titles consisting of a single word are discouraged, and in most cases are disallowed outright.
  • Read Where should I post X? if you're not absolutely sure you're posting in the right place.
  • Please read these before you post! —
  • Posts may use any of the Perl Monks Approved HTML tags:
    a, abbr, b, big, blockquote, br, caption, center, col, colgroup, dd, del, details, div, dl, dt, em, font, h1, h2, h3, h4, h5, h6, hr, i, ins, li, ol, p, pre, readmore, small, span, spoiler, strike, strong, sub, summary, sup, table, tbody, td, tfoot, th, thead, tr, tt, u, ul, wbr
  • You may need to use entities for some characters, as follows. (Exception: Within code tags, you can put the characters literally.)
            For:     Use:
    & &amp;
    < &lt;
    > &gt;
    [ &#91;
    ] &#93;
  • Link using PerlMonks shortcuts! What shortcuts can I use for linking?
  • See Writeup Formatting Tips and other pages linked from there for more info.