Decode URL in bash

Question

I'm trying to decode GET arguments in pure bash.

I.e.: hello+%26+world should become hello & world

So far I've managed to get this:

#!/usr/bin/sh
echo "Content-type: text/plain"
echo ""

CMD=`echo "$QUERY_STRING" | grep -oE "(^|[?&])cmd=[^&]+" | sed "s/%20/ /g" | cut -f 2 -d "="`
CMD="${CMD//+/ }"

echo $CMD

which replaces all the + with a space.

Is there a better way to do this? Or do I just have to look for each possible encoded special character and replace it?

anubhava · Accepted Answer · 2015-02-03 22:26:24Z

10

You can use this function for URL decoding:

decodeURL() { printf "%b\n" "$(sed 's/+/ /g; s/%\([0-9a-f][0-9a-f]\)/\\x\1/g;')"; }

Then test it as:

decodeURL <<< 'hello+%26+world'
hello & world

Explanation:

printf %b - expands backslash escape sequences in the corresponding argument
s/+/ /g - Replace each + by a space
s/%$[0-9a-f][0-9a-f]$/\\x\1/g - Replace each % followed by 2 hex characters by literal \x and same hex characters so that printf can print equivalent ASCII character for it

answered Feb 3, 2015 at 22:26

anubhava

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5 Comments

Juicy Over a year ago

Thanks, that seems to work, but how can I execute this? The string returned is a command like ls -al that I would like to execute and print the results

angerelle Over a year ago

I had to match on the capital hex characters as well: s/%$[0-9a-fA-F][0-9a-fA-F]$/\\x\1/g

anubhava Over a year ago

Yes that's right @angerelle. gnu sed also supports /i mode for ignore case matching.

toddcscar Over a year ago

Here is an example in a script where I assign the result to a variable. I had to add an extra \\ before the x . The example is taking parameter 3 in a shell script file . export DECODE_URL=`printf "%b\n" "$(echo $3 | sed 's/+/ /g; s/%$[0-9a-fA-F][0-9a-fA-F]$/\\\\x\1/g;')"` `

AnrDaemon Over a year ago

I'd remove the \n if I were you. Don't alter the input, it is not your call to make. Also, the [...] stuff is unnecessary, since URL encoding requires % to be %%-encoded as well.

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