Using the bash sort command within variable-length filenames

Question

I am trying to numerically sort a series of files output by the ls command which match the pattern either ABCDE1234A1789.RST.txt or ABCDE12345A1789.RST.txt by the '789' field.

In the example patterns above, ABCDE is the same for all files, 1234 or 12345 are digits that vary but are always either 4 or 5 digits in length. A1 is the same length for all files, but value can vary so unfortunately it can't be used as a delimiter. Everything after the first . is the same for all files. Something like:

ls -l *.RST.txt | sort -k +9.13 | awk '{print $9} ' > file-list.txt

will match the shorter filenames but not the longer ones because of the variable length of characters before the field I want to sort by.

Is there a way to accomplish sorting all files without first padding the shorter-length files to make them all the same length?

Answer 1

Perl to the rescue!

perl -e 'print "$_\n" for sort { substr($a, -11, 3) cmp substr($b, -11, 3) } glob "*.RST.txt"'

If your perl is more recent (5.10 or newer), you can shorten it to

perl -E 'say for sort { substr($a, -11, 3) cmp substr($b, -11, 3) } glob "*.RST.txt"'