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Re: localization of $_

by japhy (Canon)
on Feb 28, 2001 at 00:07 UTC ( #61153=note: print w/replies, xml ) Need Help??

in reply to localization of $_

Module code should localize any special variables it uses in each location it uses them. This is a smart and sane practice. Watch:
package MyConfigReader; sub readConfig { my ($file,$var) = @_; open FILE, "< $file" or die "can't read $file: $!"; while (<FILE>) { chomp; my ($k,$v) = split /=/, $_, 2; return $v if $k eq $var; } close FILE; return; }
That looks innocent, right? Watch it get blown to hell:
use MyConfigReader; $/ = "not gonna happen"; MyConfigReader::readConfig("whatever.dat");
My program has just modified the input record separator variable. The module relied on that being \n, and now it isn't.
sub readConfig { my ($file,$var) = @_; local ($_, $/); $/ = "\n"; # rest of function }
So yes, this is something you should be doing. Trusting the user is potentially silly. Perhaps there should be a switch like -T that catches blind use of "true globals" like you demonstrated.

japhy -- Perl and Regex Hacker

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