Normalizing Path Names with Bash

“Each time a dir/.. match is found, variable expansion with
substitution is used to remove the matched part of the path.

“Regular expressions were introduced in bash 3.0. Bash 3.2
changed regular expression handling slightly in that quotes around
regular expressions became part of the regular expression. So, if
you have a version of bash (with regular expression support) and
the code doesn’t work, put the regular expression in the while loop
in quotes.”

Complete
Story