How to decode URL-encoded string in shell?

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