Try saying out loud what you want to match: I want everything from the beginning of the line to the last backslash,

^.*\\

then possibly some more stuff

.*

and then the end of the line.

$

So, seems like it oughta be:

if ( $line =~ m/^(.*)\\.*$/ ) { ... }
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As long as the directory-only lines always end with a backslash. Does that one work for you?