Re: On using $_ in subroutines

> Bryan R Harris wrote:
>>> Bryan Harris wrote:
>>>> John W. Krahn wrote:
>>>>> Bryan Harris wrote:
>>>>>> ... but by modifying $_ I was clobbering $_ elsewhere in the larger
>>>>>> program!
>>>>> Yes because $_ is a special global variable.  This effect is called
>>>>> "action at a distance" which is why it is better to use named lexically
>>>>> scoped variables instead of $_.
>>>> I have the Perl Bookshelf on CD (and perldoc, obviously) -- where can I
>>>> read
>>>> more about this?
>>> perldoc perlvar
>>> 
>>> http://shoebox.net/articles/perl-warts.html
>>> http://en.wikipedia.org/wiki/Action_at_a_distance_(computer_science)
>> 
>> Great info, thanks.
>> 
>> Curiously, perlvar seems to recommend localizing $_ with "local", but I
>> thought I read somewhere to never use local and only use my.  I still don't
>> understand how those two are different.
> 
> local() only works on variables that are in the symbol table, in other
> words package variables.  All variables that are a single puntuation
> character are package variables and some are global and effect all
> packages.  local() does not create a variable it just masks the current
> value of a variable within the current scope.
> 
> my() creates variables that are not in the symbol table and are visible
> only within the current block or file.


Ah, that cleared it up.  Thanks, John.

- Bryan




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