Re^2: read multiple record data and populate in a new data stucture

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Re^3: read multiple record data and populate in a new data stucture by stevemayes (Scribe) on Jun 30, 2009 at 06:03 UTC
new at Perl myself but I couldn't see that anyone had answered your query "what is $_?". $_ is one of Perl's built-in variables - it is the default variable (i.e. what's currently being input or matched) and frequently if not explicitly set it will be assumed. These pairs are all the same: (these examples are from perlvar (http://perldoc.perl.org/perlvar.html) `$_ The default input and pattern-searching space. The following pairs are + equivalent: while (<>) {...} # equivalent only in while! while (defined($_ = <>)) {...} /^Subject:/ $_ =~ /^Subject:/ tr/a-z/A-Z/ $_ =~ tr/a-z/A-Z/ chomp chomp($_)` [download] It's a very important variable to get your head around so do ask in the Chatterbox if you're unsure. (at least that's what I would do).	[reply] [d/l]
Re^3: read multiple record data and populate in a new data stucture by Marshall (Canon) on Jun 30, 2009 at 05:34 UTC
This reply wasn't addressed to me, but here is an explanation for you: undef as an lvalue is one way of "throwing away" a value from the right hand side of the "=". This is actually very similar to the way that 'C' does it with an input format statement. `my @a = (1,2,3,4,5); (undef, my @b) = (@a); print "@b\n"; #prints: 2 3 4 5 (the 1 is gone)` [download] Perl has another way, a "list slice" and I prefer this in my Perl code to the 'C' way. For example to "get rid" of the "2": `my @a = (1,2,3,4,5); my @b = @a[0,2..4]; print "@b\n"; #prints: 1 3 4 5` [download] As far as the third parameter to split being -1, I see no reason for this at all as this means "no limit", the default. There are reasons to "limit" the number of things returned from split(), but I don't see it here. `my $text = "1 2 3 4 5 6"; my @tokens = split(/\s+/,$text,2); foreach (@tokens) { print "$_\n"; } #prints: 1 2 3 4 5 6` [download] The above code limits the split to 2 things.	[reply] [d/l] [select]