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.


> > > > > Oddly, perl won't let me do "my ($_) = shift;", so I'm stuck having to use
> > > > > another variable.
> > > > Perl 5.10 *will* let you do "my $_".
> > > Why is perl on OS X still at 5.8.8?  It's free, right?  why wouldn't Apple
> > > include the latest one?  (I know this isn't an Apple list, just wondering if
> > > anyone knows.)
> > Perl 5.10 is still at the .0 stage (5.10.0) and a lot of people like to
> > wait until software has progressed past the .0 phase.
>
> Makes sense.  What happened to Perl 5.9?

As of Perl 5.6 the odd numbered versions (5.7 and 5.9) are for 
development only.




John
--
Those people who think they know everything are a great
annoyance to those of us who do.        -- Isaac Asimov

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