On Sat, 25 May 2002, mark wrote:
> What is happening here exactly and what precisely does the /c do in this
> statement? I've had a couple of answers that I do not understand and thus
> far I've been told that /c "complements" the SearchPattern. OK
I'm sorry that my original reply didn't help you. Let me try once
more. You know, I don't mean to sound rude, but I get the feeling that
you're making a similar kind of mistake as I often do when asking such
questions: Trying to clever, and making guesses at what the answer
will be, which then keeps you from understanding it.
If I'm right, try to step back a bit and get a new perspective. If
not, well, never mind me.
> So my question is (drumroll) : Do I take it to mean that /c also adds the
> negative values of the given SearchPattern to the SearchPattern? Otherwise,
> what is the "complement of /a-z/ if not /-(a-z)/ ?
I think you have it almost right actually, only thing is, I don't
quite understand you...
Hum, what does perldoc say to this? perldoc perlop says:
tr/SEARCHLIST/REPLACEMENTLIST/cdsUC
y/SEARCHLIST/REPLACEMENTLIST/cdsUC
Transliterates all occurrences of the characters
found in the search list with the corresponding
character in the replacement list.
Okay, I think you're with me thus far :-)
It gets more interesting here:
Options:
c Complement the SEARCHLIST.
d Delete found but unreplaced characters.
yada yada...
If the `/c' modifier is specified, the SEARCHLIST
character set is complemented.
This means: Take all the characters *not* in the SEARCHLIST and look
for those.
If the `/d' modi
fier is specified, any characters specified by
SEARCHLIST not found in REPLACEMENTLIST are
deleted.
So, delete everything we don't have a replacement for. Do you
understand these two concepts now? If not, try typing this in your
favorite shell:
perl -ple'tr/abc//d'
Play around a bit with it, give it a few lines to process and see what
comes out... Then this:
perl -ple'tr/abc//cd'
Note the difference...
Now, let's have another look at your original line:
$name =~ tr/a-zA-Z0-9-_ .,:;'&$#@!*()?-//cd;
The searchlist here is "a-zA-Z0-9-_ .,:;'&$#@!*()?-", the replacement
list is "". Then /c comes along and complements the searchlist, so
that now all characters not in the set "a-zA-Z0-9-_ .,:;'&$#@!*()?-"
are looked for.
Since there we have REPLACEMENTLIST (or else it's empty), we can't
replace anything, but /d tells us to delete all the characters we
cannot replace, so what do we do? Delete all the (matching) characters
we find.
In effect: look for all characters not in "a-zA-Z0-9-_.,:;'&$#@!*()?-"
and delete them.
I hope this reply is more useful than my last.
Elias
--
Gefängnis für Hans Mustermann wegen
Fälschung und Verrat
-- Die Einstürzenden Neubauten, Was ist ist
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