Re^2: string diff and compare

So, fwiw, I had to do the following to your code to get your method to work the way I wanted and cover all corner cases I've tested. (If the change spans to the very last character for example, then your first condition fails and you never assign $+[0] to $lsubscr ... So I had to do the following.

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  ($rold ^ $rnew) =~ /^\0*/ and my $lsubscr = (-$+[0] + 1 && $+[0]) ? 
+-$+[0] + 1 : length $new;
   my $losubscr = ($lsubscr == length $new) ? length $old : $lsubscr;
   substr $old, $losubscr, 0, '</span>';
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This was to fix if the difference was the very last string char and one character is missing from another. Like in the case of data like:

All sentences end with what
All sentences end with what?
[download]

In this case the difference is -1, but because I had to add one to it, it was set to 0. But 0 is the beginning of the string, not the character just past the end of the string.

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Re^3: string diff and compare by raybies (Chaplain) on May 08, 2012 at 11:45 UTC
So for the sake of completeness, and posterity... and not because anyone cares, here's the final version that I decided fixed things up the way I wanted. Turns out by reordering the substr I was able to remove the space ambiguity I was seeing in one of my example data failures where I was getting nested span tags. `sub spandiffstr { my ( $old, $new ) = @_; my $span = '<span>'; my $espan = '</span>'; ( $old ^ $new ) =~ /^\0/ and my $subscr = $+[0]; substr $old, $subscr, 0, $span; substr $new, $subscr, 0, $span; my ( $rold, $rnew ) = map scalar reverse, $old, $new; ( $rold ^ $rnew ) =~ /^\0/ and my $lsubscr = -$+[0]; my $losubscr = $lsubscr; unless ($lsubscr) { $losubscr = length $old; $lsubscr = length $new; } substr $old, $losubscr, 0, $espan; substr $new, $lsubscr, 0, $espan; return $old, $new; }` [download] Thanks for all the fish!	[reply] [d/l]

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Re^3: string diff and compare
by raybies (Chaplain) on May 08, 2012 at 11:45 UTC

sub spandiffstr {
    my ( $old, $new ) = @_;
    my $span = '<span>';
    my $espan = '</span>';
    ( $old ^ $new ) =~ /^\0*/ and my $subscr = $+[0];
    substr $old, $subscr, 0, $span;
    substr $new, $subscr, 0, $span;
    my ( $rold, $rnew ) = map scalar reverse, $old, $new;
    ( $rold ^ $rnew ) =~ /^\0*/ and my $lsubscr = -$+[0];
    my $losubscr = $lsubscr;
    unless ($lsubscr) {
      $losubscr = length $old;
      $lsubscr = length $new;
    }
    substr $old, $losubscr, 0, $espan;
    substr $new, $lsubscr, 0, $espan;
    return $old, $new;
}
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