Learned something new yesterday that's such a basic construct of Perl that I'm embarrassed to admit it, but in case someone else out there needs a refresher or didn't know this, here goes:

The foreach (and for and map, etc) command can be used to modify the list that it is iterating over. I know. I should've known this. I don't know how many times I've wanted to modify an array and had to create my own index because I didn't realize that if I had something like: 

my @x = (1..10);
foreach (@x) {
    $_ += 100;
}
print "@x"; 

OUTPUT: 
101 102 103 104 105 106 107 108 109 110

[download]

I guess I just assumed it didn't because when you declare the variable in a foreach loop, you don't think of it as a reference (because it really isn't one, but it sorta acts like one in that it represents the actual element in the list.) I had always figured that $_ was simply a copy of what was in the array, not the actual element. But apparently Perl is cooler than that. ;)

SO in this example: $element can be modified in the array. 


my @x = (1..10);
foreach my $element (@x) {
    $element += 100;
}
print "@x"; 

OUTPUT: 
101 102 103 104 105 106 107 108 109 110

[download]

Anyhow, the discovery was a delighful suprise, that I came across while preparing to brief a bunch of nonPerl users on Perl. This presentation's been a great way to really fill in the many cracks I have about my understanding of basic Perl programming. (I'm up to about 60 Power point slides... poor suckers attending this meeting are going to slip into a comma... death by Powerpoint! Buwahahaha)

I also tested these loops constructs and observed they altered the loop array elements in the same way...: 

 map {$_ += 100} @x;

(yields same output and alters @x as does...)
 
$_ += 100 for @x; 

in case you wondered... :)

[download]

In reply to Perlplexation - foreach shoulda Known by raybies

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