|Perl: the Markov chain saw|
Re: what is the translation?by BrowserUk (Pope)
|on Jul 20, 2011 at 03:23 UTC||Need Help??|
What is the tr/!-~/P-~!-O/ doing?
tr is perl's transliteration function.
It translates the characters in the string it is applied to, according to the two tables of characters given as its arguments.
For $string =~ tr/123/ABC/, it would change any and all occurrences of the characters '1','2', or '3', for the characters 'A', 'B', and 'C' respectively. Ie. If $string contained "a1b2c3c3b2a1", after the above code it would then contain "aAbBcCcCbBaA".
In your example, the first list is specified as: !-~ which is a short-hand notation meaning all the characters between '!' and '~', That is all the visible characters in the (7-bit) ASCII character set. Eg:
The second list, P-~!-O specifies the same characters, but in a different order, as two ranges. 'P' through '~' and '!' through 'O'. Effectively,
The effect of these tables is that '!' will be translated to 'P' (and 'P' will become '!'); '"' will become 'Q' (and 'Q' becomes '"') and so on.
This is a reversible (obfuscation) process similar to ROT13. Effectively "ROT47".
However, why this is being applied to the input data, your guess is as good as mine. Probably better :)
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