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;
}

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That looks innocent, right? Watch it get blown to hell: 
use MyConfigReader;

$/ = "not gonna happen";
MyConfigReader::readConfig("whatever.dat");

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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
}

[download]
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

In reply to Re: localization of $_ by japhy
in thread localization of $_ by modred

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