Substituting across lines using s///gs

[R (Chandra) Chandrasekhar]

Dear Folks,

This is a question about s///sg across lines from a file slurped in file mode.
I am trying to change occurrences of & into &. As a minimal example, I used 
the contrived file below where single- and multi-line records are delimited by 
<...>. The only real-world text is a hyperlink from an actual web site.
--------
<Pebbles & Pelicans>
<Hogsworthy Tales of a Late Summer Afternoon>
<Everything News
worthy & Printable>
# This is a comment and should be ignored
<Rough &amp; Tumble>
<Pride & Prejudice>
<P&O Shipping Corporation>
<a 
href=http://www.amazon.com/s?ie=UTF8&tag=mozilla-20&index=blended&link%5Fcode=qs&field-keywords=Programming%20Perl&sourceid=Mozilla-search>
<This record should not be
modified.>
<Nor this.>
<This is a very long line with many intervening & symbols This is a very long 
line with many intervening & symbols This is a very long line with many 
intervening & symbols This is a very long line with many intervening & symbols 
This is a very long line with many intervening & symbols This is a very long 
line with many intervening & symbols This is a very long line with many 
intervening & symbols This is a very long line with many intervening & symbols>
<sudo apt-get update && sudo apt-get upgrade>
--------

I tried this script on the above file:
--------
#!/usr/bin/perl
use warnings;
use diagnostics;
use strict;

my ($fh, $file, $data, $count, @record, $record);
my (@orig, $orig, @repl, $repl, $subs, @amper);

undef $/; # Slurp data in file mode
$file = shift;

open $fh, '<', $file or die "Cannot open $file: $!\n";
$data = <$fh>;
$count = 0;
while ($data =~ m|<\s*?(.*?)\s*?>|gis)
    {
    $count++;
    print "$count: $1\n";
    push @record, $1;
    }
close $fh;

$count = 0;
foreach $record (@record)
    {
    $count++;
    if (($record !~ m|&amp;|s) && ($record =~ m|&|s))
        {
        push @orig, $record;
        push @amper, $count;
        $subs = ($record =~ s|&|&amp;|gis); # Should be number of substitutions
        if ($subs == 0) {warn "$count: No replacement made.\n";}
        else {print "$count: $subs replacement(s) made.\n";}
        push @repl, $record;
        }
    }

foreach $orig (@orig)
    {
    $subs = 0;
    $repl = shift @repl;
    $count = shift @amper;
    $subs = ($data =~ s|$orig|$repl|gs);
    if ($subs == 0) {warn "$count: No replacement made.\n";} # Why?
    else {print "$count: $subs replacement(s) made.\n";}
    }

open $fh, '>', "$file.new" or die "Cannot open $file: $!\n";
print $fh $data;
close $fh;
--------

Why does the hyperlink string alone not get substituted at the end although the 
replacement string has been correctly altered with five substitutions?

Many thanks for your patience reading this long email.

Chandra
05 Feb 08

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