Re: Split ( ) is Giving Me a Splitting Headache

OK Im a little confused now - I see where and why he is getting his error above and that $_ is undefined. In my example below - I see the first print statement which I beleive to be equivelant to the ops print statement. But Im confused about my second print statement - where and how is $_ getting set? Is split setting it?

from perldoc -f split:

If EXPR is omitted, splits the $_ string.  If PATTERN is also omitted,
+ splits on whitespace (after skipping any leading whitespace).  Anyth
+ing matching PATTERN is taken to be a delimiter separating the fields
+.  (Note that the delimiter may be longer than one character.)
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EXPR is not omitted, PATTERN is not omitted - where is $_ coming from? Is there some documentation someone can point out that explains this behavior?

#!/usr/bin/perl
use warnings;
use strict;

print "$_\n" for split ( "Hello World" );
 
print "$_\n" for split /\s+/, "Hello World";
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UPDATE
OK I see in perlvar that for is setting it and split is not my culprit.

Here are the places where Perl will assume $_ even if you don't use it
+:
__snip__
- The default iterator variable in a foreach loop if no other variable
+ is supplied.
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But why is for not setting it in the first print statement?

UPDATE #2
from the following looks like $_ is an empty hash?

#!/usr/bin/perl
use warnings;
use strict;
use Data::Dumper;

print "\n\n";
print "\$_ = $_\n";

print "\n\n";
for ( 1 .. 10 ) { print "\$_ = $_\n" }

print "\n\n";
print $_ for {};

print "\n\n";
print Dumper $_ for {};

print "\n\n";
my $count = 0;
for ( sort keys %{ $_ } ) { print $count++, ":$_{$_} $_\n" };
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Now Im really confused.

Ted
--
"That which we persist in doing becomes easier, not that the task itself has become easier, but that our ability to perform it has improved."
--Ralph Waldo Emerson

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Re^2: Split ( ) is Giving Me a Splitting Headache by bpphillips (Friar) on May 25, 2006 at 11:24 UTC
The key here is what happens when you perform the incorrect usage of `split`: `my @parts = split( "Hello World" ); # generates warning print "Parts: " . scalar(@parts) . "\n"; # prints "Parts: 0" for( @parts ){ # never enters this loop since the array is empty print "$_\n"; }` [download] The warning you saw on your first loop was generated by the `split` statement, not the `print` statement. As demonstrated above, the `print` statement never gets executed because the loop is never entered. Hope that helps make some sense of what's happening, -- Brian	[reply] [d/l] [select]

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Re^2: Split ( ) is Giving Me a Splitting Headache
by bpphillips (Friar) on May 25, 2006 at 11:24 UTC

split

my @parts = split( "Hello World" ); # generates warning
print "Parts: " . scalar(@parts) . "\n"; # prints "Parts: 0"

for( @parts ){ # never enters this loop since the array is empty
    print "$_\n";
}
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split

print

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