Thank you, tye, for the insight and advice.

I met this problem recently while working on the original version of this script, from the module Pod-Tree-1.06. Path strings containing '\' were passed to the script as arguments by the user (me), and the script hit the error while doing the substitution

$dir =~ s/^$PodDir/$HTMLDir/o;
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I did not understand the problem at the time, but I found that I could fix it by inserting

# fix up the Win32 paths
$PodDir  =~ s( \\ )(/)gx;
$HTMLDir =~ s( \\ )(/)gx;
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Now you explained the nature of the problem and showed two ways to make similar scripts more robust:

• Apply quotemeta or \Q\E to a user-supplied string before using it in a regex.
• File::Spec provides platform-independent operations on path strings, notably splitting, catenating and converting absolute paths to relative, and should be used in portable scripts.

Rudif