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Re: Unlocking the Dark Mysteries of Acme::Bleachby broquaint (Abbot)
|on Jun 29, 2003 at 22:05 UTC||Need Help??|
Let's break it down then
Open the filename name stored in the global variable $0 (which stores the name of the script perl was called with) and assign a filehandle to 0 (this is a rather obscure feature of open). If it can't be opened then print out an error message and exit the program.
Slurp in the contents of the 0 filehandle (the program code), join them into a single string and assign them to $shirt, then immediately perform a replace on it by removing everything before and including use Acme::Bleach.
Locally change the __WARN__ handler to dirty() which returns true if a warning matches non-whitespace (likely to supress any warnings in the code that follows).
Unless the contents of $shirt (the program code) matches non-whitespace or doesn't begin with $tie (a sequence of 8 space and tab alternations) then evaluate the return of brighten $shirt and exit (this is the bit that is run post-bleaching).
Locally assign $_ to the last element of @_, which is the program code (the is $_ localised so it isn't clobbered and also sets it as the current topicalizer). Remove a leading $tie (the tabs) or any non space/tab characters. The tr will change every space to 0 and every tab to 1 and the pack then converts it back to it's original form (ready to be evaluated).
Reopen the the script in $0 for writing (to be bleached in this case).
Use the alternate syntax of print to write use Acme::Bleach; and the return of whiten $shirt to the 0 filehandle then exit.
Once again, $_ is localised and is assigned a bit string created by unpack of the last element of @_ (the contents of $0 in this case). Replace all the 0s and 1s as spaces and tabs respectively and return the modified $_ with $tie prepended.
So basically Acme::Bleach converts the contents of the code into a bitstring of spaces and tabs on the first run, and then on subsequent runs uncompresses the bitstring and runs the code. Simple as that :)
update: $tie comment now correct and further explanation of the warning handler localisation