in reply to I need a simple explantion of the difference between my() and local()

The difference between my and local is just one of scope. All subroutines called from the context of a local variable can access that variable, but not the my variable: 
sub foo {
    local $a = 10;
    my $b = 20;
    bar();
}

sub bar {
    print "A: $a\n"; # Just fine
    print "B: $b\n"; # Warning from -w
}

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If a piece of code needs to use local in this way, it's could probably be rewritten in a cleaner way. If my works, you should definitly use it.

I won't condemn all use of local, however. I believe there are situations where you need to use local for dynamically generated anonymous functions, perhaps for use with $SIG{XYZ}. Can anyone confirm or deny this? I just remember writing signal code once where I needed to use local. (Of course, this is before I learned about the signal handling packages at CPAN.)

-Ted

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Re: Scope Difference
by TGI (Parson) on May 02, 2001 at 21:55 UTC

    A good use of local is when you are tweaking a special variable.

    Let's say you want to slurp a whole file into a scalar. Your code would look something like this:

    my $file;
{   local $/;
    open (FILE, "<$foo") or die "Unable to open $foo: $!";
    $file = <FILE>;
    close FILE;
}

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    By enclosing the modification of $/ in a block, you avoid surprises down the road. $/ only has its value changed within that block.


    TGI says moo

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[d/l]
      By narrowing the block that holds the local, you can further contain the effect. 
        open(FILE, "<$foo") or die "$foo: $!";
  my $file = do { local $/; <FILE> };
  close(FILE);

      [download]
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[d/l]

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