$filename='Z:\repo\bin\tools\scripts\shared\users\script.pl';
$key =~ /\Q$filename\E/i;

#matches (notice different starts and ends)
Z:\repo\bin\tools\scripts\shared\users\script.pl
Z:\repo\bin\tools\scripts\shared\users\script.plm
Z:\repo\bin\tools\scripts\shared\users\script.plx
Z:\repo\bin\tools\scripts\shared\users\script.pl\foobar
\\?\Z:\repo\bin\tools\scripts\shared\users\script.plm

# and does NOT match
Z:/repo/bin/tools/scripts/shared/users/script.pl