How do I decode or create those %-encodings on the web?

(contributed by brian d foy)

Those % encodings handle reserved characters in URIs, as described in RFC 2396, Section 2. This encoding replaces the reserved character with the hexadecimal representation of the character's number from the US-ASCII table. For instance, a colon, :, becomes %3A.

In CGI scripts, you don't have to worry about decoding URIs if you are using CGI.pm. You shouldn't have to process the URI yourself, either on the way in or the way out.

If you have to encode a string yourself, remember that you should never try to encode an already-composed URI. You need to escape the components separately then put them together. To encode a string, you can use the the URI::Escape module. The uri_escape function returns the escaped string:

	my $original = "Colon : Hash # Percent %";

	my $escaped = uri_escape( $original );

	print "$escaped\n"; # 'Colon%20%3A%20Hash%20%23%20Percent%20%25'

To decode the string, use the uri_unescape function:

	my $unescaped = uri_unescape( $escaped );

	print $unescaped; # back to original

If you wanted to do it yourself, you simply need to replace the reserved characters with their encodings. A global substitution is one way to do it:

	# encode
	$string =~ s/([^^A-Za-z0-9\-_.!~*'()])/ sprintf "%%%0x", ord $1 /eg;

	#decode
	$string =~ s/%([A-Fa-f\d]{2})/chr hex $1/eg;