That's a clever way of doing it. Of course its only useful if the subroutine you are writing is expecting exactly 0 or 1 argument.

If the subroutine allows multiple arguments with only some being optional, the above approach will not work.

Well, it works if the optional arguments are all trailing.

sub lotsaArgs {
   my $arg1 = 'default';
   $arg1 = shift if @_;

   my $arg2 = 'default';
   $arg2 = shift if @_;

   my $arg3 = 'default';
   $arg3 = shift if @_;

   my $arg4 = 'default';
   $arg4 = shift if @_;
...
}
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This would be analogous to default arguments in C++, for instance.

If you want to have named arguments, and only pass some of them, then the hash of default values and

my %args=(%defaults,@_);
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as suggested below is obviously better.

But as asked, he seemed to have only one arg to default.
--
Mike

If you wanted to avoid using a hash of named arguments for whatever reason, but wanted to avoid typing

my $argN="default";
$argN=shift if @_;
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repeatedly, perhaps the following would be useful :


&foo (1,2,3);

sub foo {
    my @defaults= qw (foo bar baz quux quuz boo);
    for (1.. @_) {shift @defaults};
    @_= (@_, @defaults);
    ($a1, $a2, $a3, $a4, $a5, $a6) = @_;    
    print join "\n",$a1, $a2, $a3, $a4, $a5, $a6;
}
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This doesn't check that a user's supplied too many parameters, but that shouldn't be too hard to add in.
Of course, as mentioned elsewhere, this is all moot once // comes into play, but it's an interesting mental exercise.

An additional note : this assumes that parameters are given in "least optional" to "most optional"; if you have 6 params and only #2 is optional, this won't do it for you.