How to decode URL-encoded string in shell?

Question

I have a file with a list of user-agents which are encoded. E.g.:

Mozilla%2F5.0%20%28Macintosh%3B%20U%3B%20Intel%20Mac%20OS%20X%2010.6%3B%20en

I want a shell script which can read this file and write to a new file with decoded strings.

Mozilla/5.0 (Macintosh; U; Intel Mac OS X 10.6; en

I have been trying to use this example to get it going but it is not working so far.

$ echo -e "$(echo "%31+%32%0A%33+%34" | sed 'y/+/ /; s/%/\\x/g')"

My script looks like:

#!/bin/bash
for f in *.log; do
  echo -e "$(cat $f | sed 'y/+/ /; s/%/\x/g')" > y.log
done

Answer 1

Here is a simple one-line solution.

$ function urldecode() { : "${*//+/ }"; echo -e "${_//%/\\x}"; }

It may look like perl :) but it is just pure bash. No awks, no seds ... no overheads. Using the : builtin, special parameters, pattern substitution and the echo builtin's -e option to translate hex codes into characters. See bash's manpage for further details. You can use this function as separate command

$ urldecode https%3A%2F%2Fgoogle.com%2Fsearch%3Fq%3Durldecode%2Bbash
https://google.com/search?q=urldecode+bash

or in variable assignments, like so:

$ x="http%3A%2F%2Fstackoverflow.com%2Fsearch%3Fq%3Durldecode%2Bbash"
$ y=$(urldecode "$x")
$ echo "$y"
http://stackoverflow.com/search?q=urldecode+bash