Using ampersands and parens when calling a Perl sub

Question

#!/usr/bin/perl

sub t {
  print \"in t\\n\";
  print \"@_\\n\";
  &s;
}

sub s {
  print \"in s\\n\";
  print \"@_\\n\";
}

t(1,2);
print \"out\\n\";
print \"@_\\n\         


        

Answer 1

Calling a subroutine using the &NAME; syntax makes current @_ visible to it. This is documented in perlsub:

If a subroutine is called using the & form, the argument list is optional, and if omitted, no @_ array is set up for the subroutine: the @_ array at the time of the call is visible to subroutine instead. This is an efficiency mechanism that new users may wish to avoid.

So, it's definitely a feature.

Answer 2

Straight from the camel's mouth:

If a subroutine is called using the ``&'' form, the argument list is optional, and if omitted, no @_ array is set up for the subroutine: the @_ array at the time of the call is visible to subroutine instead. This is an efficiency mechanism that new users may wish to avoid.

Answer 3

When using & before the sub name and no argument list is passed, the current @_ is passed as argument instead. So, it is a feature.

Here are the different ways to call a subroutine:

NAME(LIST); # & is optional with parentheses.
NAME LIST;  # Parentheses optional if predeclared/imported.
&NAME(LIST); # Circumvent prototypes.
&NAME;      # Makes current @_ visible to called subroutine.

from perldoc perlsub