lunarny

#!/usr/bin/perl
print while $_=$_{$_};
$_='OTcommailDngATghiliaguans';
1 while s/(.{5})(.{5})?/$_{$2}=$1,$2/e;
print while $_=$_{$_};

spydoor

well I'll do my best...I'm no expert

print while $_=$_{$_}; # does nothing $_ is empty

$_='OTcommailDngATghiliaguans'; # initialize $_

1 while s/(.{5})(.{5})?/$_{$2}=$1,$2/e;

? match 0 or 1 (nongreedy)
() () in regurlar expressions puts the matching expression in $1.. $2..
e means eval second part of regular expression.
.{5} means match any 5 characters

What this is doing is looping through the string and building a hash like
$_{$2}=$1
$_{'mailD'} = OTcom;
$_{'ngATg'} = mailD;
$_{'hilia'} = ngATg;
$_{'guans'} = hilia;
$_{''} = guans;

one important thing to keep in mind is that $_ the scalar, is a different variable from $_{} the hash


you can run this to see whats going on in the while loop

,$2 causes the value of $2 to get trucated from $_ after each loop..... not sure why

print while $_=$_{$_}; #This will loop through the hash and print it.

after the regular expression, $_ = ''

but we built a hash where $_{''} = 'guans', so that gets printed
now assign $_ = 'guans';

then $_{'guans'} = hilia, so print that
now assign $_ = 'hilia' .......

until we try $_{'OTcom'} which doesn't exist, so the loop is ended.

result :
guanshiliangATgmailDOTcom is printed.


so in other words it's a very cryptic way to print the string out backwards 5 character chunks at a time, but you probably knew that part

peace_of_mind

Please tell all this wasn't just to decipher someone's sig/email addy. lol

__________________
Amateurs built the ark
Professionals built the Titanic

lunarny

Thank you very much.

"$2 causes the value of $2 to get trucated from $_ after each loop..... not sure why ?"

s/(.{5})(.{5})?/$_{$2}=$1,$2/e;
my opinion, the sentence above has two function:
s/(.{5})(.{5})?/$2/; (substitute $1$2 with $2)
$_{$2}=$1,(input $1 into hash)
I think the role of "/e" is to disreagard all components before "," when substitution begins. so for
s/(.{5})(.{5})(.{5})?/$_{$2}=$1,$2,$3/e;
will substitute $1$2$3 with $3.

"so in other words it's a very cryptic way to print the string out backwards 5 character chunks at a time, but you probably knew that part"

I don't know it before. Your help is really valuable.
Thanks.
I don't know hash before.
An interesting thing is that if you use "$_=worldpeacewalksaway?world" The script will go on and on.
I don't know if it is because we have the same two keys "world" here for hash.
Have you heard of it? thanks!

spydoor

Yes, because 'world' is there twice, it loops infinitely.
You need to understand what a hash (associative array) is, to really see what is going on.

For this example it's functioning like a lookup table.

$_{KEY} = VALUE

$_{'peace'}='world'
$_{'walks'}='peace'
$_{'away?'}='walks'
$_{'world'}='away?'
$_{''}='world'

while $_ = $_{$_}; # loop while I get a VALUE; assign KEY=VALUE after each iteration

lunarny

Thank you, Spydoor.
I understand now. for $_ = $_{$_}; I didn't notice the "$_" is changing before, I simply thought it would print the hash. But actually, it didn't exactly print hash. It needs the value from hash, but has its own process.
You're very clever. Thanks for your friendliness.


hui