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:

!"#$%&'()*+,-./0123456789:;<=>?@ABCDEFGHIJKLMNOPQRSTUVWXYZ[\]^_`abcdef
+ghijklmnopqrstuvwxyz{|}~

[download]

The second list, P-~!-O specifies the same characters, but in a different order, as two ranges. 'P' through '~' and '!' through 'O'. Effectively, 

PQRSTUVWXYZ[\]^_`abcdefghijklmnopqrstuvwxyz{|}~!"#$%&'()*+,-./01234567
+89:;<=>?@ABCDEFGHIJKLMNO

[download]

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 :)

Examine what is said, not who speaks -- Silence betokens consent -- Love the truth but pardon error.
"Science is about questioning the status quo. Questioning authority".
In the absence of evidence, opinion is indistinguishable from prejudice.

In reply to Re: what is the translation? by BrowserUk
in thread what is the translation? by roadtest

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