How to make your own function that defaults to $_:

sub myfunc {
   my $arg = @_ ? $_[0] : $_;
   for ($arg) {
      ...
   }
}
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The for is a convenient way to alias $_. (local $_ is buggy. It doesn't work well if $_ is tied or aliased to someting that's tied, and it doesn't protect pos($_).) Of course, you could just work with $arg directly instead of aliasing $_ to it.

The use of a lexical ($arg) allows us to modify $_ without affecting the argument in the caller. If you don't modify $_, the above can be simplified to

sub myfunc {
   for (@_ ? $_[0] : $_) {
      ...
   }
}
[download]