The rule with regexes is that non-alphanumeric characters (\W) lose their special meaning when escaped with a \, (\* is a litteral '*', \( is a litteral parenthesis etc...), while alphanumeric characters gain a special meaning when escaped. So \1, \2 etc... are reference to captured groups, \w means alphanumeric characters. This means that \x where x is a letter should always be considered to have a special meaning, even if this is not the case for the current version of perl, because such a meaning may be added in future versions. And yes, even interpolated variables are read using the regex syntax, and not taken litteraly.

\g is the start of a regex special meaning, referenced in perlreref:

\g1 or \g{1}, \g2 ... Matches the text from the Nth group
Since you don't have a number after you \g, this is, indeed, an incomplete pattern.

The solution is to remove its special meaning to \ (the escaping character), by adding another \ in front of it. The easiest way to do that is to use quotemeta which will leave all alphanumeric characters untouched, and escape all others (those that may have a special meaning). my $esc_bad_gitdir = quotemeta $bad_gitdit;
Or using the \Q shortcut: qr/Cannot find directory\(ies\): \Q$bad_gitdir/

Edit: there were typos everywhere...

In reply to Re: Unterminated \g... pattern in regex behaving badly on Windows by Eily
in thread Unterminated \g... pattern in regex behaving badly on Windows by jkeenan1

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