# to squish a string
y sssscccc;
The comments provided say that this "squishes" a string.
If you actually try this out in a little test program,
you'll see exactly what it does:
$_ = "bookkeeper";
y sssscccc;
print;
This prints "bokeper"--in other words, it gets rid of
consecutive letters ("oo" => "o").
Why does it do that? Let's write the statement in a
slightly different way:
tr///scccc;
This is the same statement, because:
"y" is a synonym for "tr";
and the "tr" operator can use any character to
separate the SEARCHLIST from the REPLACEMENTLIST.
So in the obfuscated example, "tr" is "y", and the
separator is "s". We can replace those to make it look
more "normal", just as we did above.
Why all the "c"'s at the end, though? Well, we can
take most of those off, too:
tr///sc;
And now we no longer have obfuscated code: this is
just the regular "tr" operator, working as advertised.
The "c" tells "tr" to complement the SEARCHLIST; the
SEARCHLIST is an empty string, so the complement is
any character--so we're searching for any character.
The "s" tells "tr" to "squish" the string--
from perlman:perlop:
If the /s modifier is specified, sequences of characters
that were transliterated to the same character are
squashed down to a single instance of the character.
In other words, "oo" => "o", and so on.
The final thing going on is that if the REPLACEMENTLIST
is empty (as it is here), the SEARCHLIST is replicated
(so the SEARCHLIST and REPLACEMENTLIST are the same).
So we're translating every character (the complement
of an empty SEARCHLIST) into itself, *unless* there's
a sequence of characters that translate to the same
character, in which case we "squish" the sequence down
to one instance of that character.
So, I hope this helps. Try to figure out the rest
yourself, using some test programs and perlman:perlop.
And if I've made any mistakes, someone please correct
them. :) |