If you don't want to match a slash, tell Perl about it:

m{/([^/]*?)/([^/]*?)/([^/]*?)\.([a-z0-9]+?)$}
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The problem can be solved using split in a much cleaner way:

my @parts = (split m{/}, '/x/y/z/a/b/c/d/e.f');
splice @parts, 0, -3;
push @parts, split /\./, pop @parts;
print "<$_>" for @parts;
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