FAQ 9.10 How do I decode or create those %-encodings on the web?


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This is an excerpt from the latest version perlfaq9.pod, which
comes with the standard Perl distribution. These postings aim to
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to review and update the answers. The latest version of the complete
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9.10: 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
"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;



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