Can I tell a sub to take $_ instead of @

statebelt has asked for the wisdom of the Perl Monks concerning the following question:

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Re: Can I tell a sub to take $_ instead of @_ (like some builtins do) by broquaint (Abbot) on Aug 22, 2002 at 18:50 UTC
`sub foo { # changing $_ is not a good idea local $_ = $_; print "\$_ is currently: $_" } foo foreach qw(one two three four); __output__ $_ is currently: one $_ is currently: two $_ is currently: three $_ is currently: four` [download] Because `$_` is global you should be able to access it from anywhere (but be careful not to mess with it!). HTH `_________ broquaint`	[reply] [d/l]
•Re: Can I tell a sub to take $_ instead of @_ (like some builtins do) by merlyn (Sage) on Aug 22, 2002 at 18:43 UTC
Well, `$_` is a global. Unless your subroutine localizes it, you are messing with the caller's `$_` anyway! -- Randal L. Schwartz, Perl hacker	[reply]
Re: Can I tell a sub to take $_ instead of @_ (like some builtins do) by no_slogan (Deacon) on Aug 22, 2002 at 18:48 UTC
You can easily write a sub so that it uses $_ if it gets no other arguments. `sub foo { my $arg = @_ ? shift : $_; ... }` [download] Or some such like that... or maybe &foo to satisfy use strict; Be very careful about using &foo. That lets foo have access to @_, which might get you in trouble. It's generally better to say foo() or maybe &foo(). Update: The other people who responded have a good point about localizing $_ if you're going to be changing it. But I don't think that's what you were asking for.	[reply] [d/l]
Re: Can I tell a sub to take $_ instead of @_ (like some builtins do) by BrowserUk (Patriarch) on Aug 22, 2002 at 19:27 UTC
A slight variation `#! perl -w sub test { my $parm = $_[0] \|\| $_; print $parm, $/; } test( "fred"); test for qw(the quick brown fox); __END__ # Output C:\test>192129 fred the quick brown fox C:\test>` [download] What's this about a "crooked mitre"? I'm good at woodwork!	[reply] [d/l]
Re x 2: Can I tell a sub to take $_ instead of @_ (like some builtins do) by Sweeper (Pilgrim) on Aug 23, 2002 at 05:44 UTC
About your line: my $parm = $_[0] \|\| $_; What is you call this? test(0); test(""); You should wait for Perl 6 and use the new operator `//`.	[reply]
Re: Re x 2: Can I tell a sub to take $_ instead of @_ (like some builtins do) by BrowserUk (Patriarch) on Aug 23, 2002 at 05:58 UTC
<tongue-in-cheek> Printing a null byte to the screen isn't very useful anyway! It's a feature:) </tongue-in-cheek> `my $parm = defined $_[0] ? $_[0] : $_;`? What's this about a "crooked mitre"? I'm good at woodwork!	[reply] [d/l]
Re: Can I tell a sub to take $_ instead of @_ (like some builtins do) by Aristotle (Chancellor) on Aug 22, 2002 at 23:11 UTC
You could write that as `sub foo { my $var = @_ ? \$_[0] : \$_; modify($$var); } foo for @list;` [download] Beware of false laziness however. You should not use this kind of interface lightheartedly. Are you sure it is a better idea than just wrapping the inside of `&foo` with a `for` loop? `sub foo { for(@_) { modify($_); } } foo @list;` [download] Makeshifts last the longest.	[reply] [d/l] [select]