I'm trying to make substitutions within a block of text using the following: 
#!/usr/bin/perl -w

use strict;

my %subs =
(

  qr/(\d+)F/i => sub { 
    warn "Matched F with $1\n";
    return sprintf("%.u" , ($1 - 32) / 1.8) . 'C'
  },
  qr/(\d+)C/i => sub {
    warn "Matched C with $1\n";
    return sprintf("%.u" , ($1 * 1.8) + 32) . 'F'
  },

);

my $html = do { local $/; <DATA> };

warn $html;

foreach my $key (keys %subs)
{
  warn "checking key: $key\n";
  $html =~ s/$key/$subs{$key}->()/eg;

  warn $html;
}

warn $html;

__DATA__
convert 180F to C
convert 180C to F
convert 30" to cm
etc

[download]
If you look at the output of the code; you'll see that once converted, the next regex converts it back.. 
convert 180F to C
convert 180C to F
convert 30" to cm
etc

checking key: (?i-xsm:(\d+)C)
Matched C with 180
convert 180F to C
convert 356F to F
convert 30" to cm
etc

checking key: (?i-xsm:(\d+)F)
Matched F with 180
Matched F with 356
convert 82C to C
convert 180C to F
convert 30" to cm
etc

convert 82C to C
convert 180C to F
convert 30" to cm
etc

[download]
I assume the solution is to use the global match modifier \G within a while loop but can't get my head around it - if possible I'd like to maintain a hash of qr's to make the code easier to maintain as I extend it. Hope someone can help point me in the right direction! Thanks

In reply to Global replace issue by Anonymous Monk

Title:
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