Were I trying to tout the advantages of Perl to a maintainance programmer who had been around the block, I would not put in comments that they would be sure to recognize as maintainance pitfalls! Instead I would go the other way: 
#! /usr/bin/perl -w 
use strict;

# Create a frequency count of all words in all input files
my %freq_count;
while (defined(my $line = <>)) {
  while ($line =~ /(\w+)/g) {
    $freq_count{$1}++;
  }
}

# Print the frequency summary.
foreach my $word (sort keys %freq_count) {
  print "$word:\t$freq_count{$word}\n";
}

[download]
There. The looping constructs are all readily explainable, there are no hidden uses of $_, and no comments that will become wrong with time. I also removed a bug in the code that you wrote (which you copied unchanged from eduardo).

Kudos to the first person to figure out what the bug is.

In reply to Re (tilly) 2: Efficiency in maintenance coding... by tilly
in thread Efficiency in maintenance coding... by eduardo

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.