The complement to basename that arturo forgot to mention is dirname, so your code would look like this:

$a = "/root/subroot/subsubroot/filename";
$b = dirname $a;
$c = basename $a;
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That said, do not get into the habit of using variables $a and $b. You are much better off giving them descriptive names, which will help your code self-document itself. A better way of writing your code would be

my $filespec = "/root/subroot/subsubroot/filename";
my $path     = dirname $filespec;
my $filename = basename $filespec;
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