Question

I am trying to write a program that is sort of similar to UNIX basename, except I can control the level of its base.

For example, the program would perform tasks like the following:

$PROGRAM /PATH/TO/THE/FILE.txt 1
FILE.txt # returns the first level basename

$PROGRAM /PATH/TO/THE/FILE.txt 2
THE/FILE.txt #returns the second level basename

$ PROGRAM /PATH/TO/THE/FILE.txt 3
TO/THE/FILE.txt #returns the third level base name

I was trying to write this in perl, and to quickly test my idea, I used the following command line script to obtain the second level basename, to no avail:

$echo "/PATH/TO/THE/FILE.txt" | perl -ne '$rev=reverse $_; $rev=~s:((.*?/){2}).*:$2:; print scalar reverse $rev'
/THE

As you can see, it’s only printing out the directory name and not the rest.
I feel this has to do with nongreedy matching with quantifier or what not, but my knowledge lacks in that area.

If there is more efficient way to do this in bash, please advise

Answer 1

You will find that your own solution works fine if you use $1 in the substitution instead of $2. The captures are numbered in the order that their opening parentheses appear within the regex, and you want to retain the outermost capture. However the code is less than elegant.

The File::Spec module is ideal for this purpose. It has been a core module with every release of Perl v5 and so shouldn’t need installing.

use strict;
use warnings;

use File::Spec;

my @path = File::Spec->splitdir($ARGV[0]);
print File::Spec->catdir(splice @path, -$ARGV[1]), "\n";

output

E:\Perl\source>bnamen.pl /PATH/TO/THE/FILE.txt 1
FILE.txt

E:\Perl\source>bnamen.pl /PATH/TO/THE/FILE.txt 2
THE\FILE.txt

E:\Perl\source>bnamen.pl /PATH/TO/THE/FILE.txt 3
TO\THE\FILE.txt