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Re: Re: GetOpt::Long usage style

by demerphq (Chancellor)
on Mar 08, 2003 at 12:32 UTC ( #241374=note: print w/replies, xml ) Need Help??


in reply to Re: GetOpt::Long usage style
in thread GetOpt::Long usage style

\(my $verbose='');

my returns what has been declared. (Although the behaviour of it as a function is a little interesting, I dont think it can be prototyped, and I can't find complete documentation for it off hand.) The parenthesis required because the precedence of the assignment operator causes

GetOptions(x=>my $x=1,y=>my $y);

to be parsed something like

GetOptions('x',(my $x=1,y=>my $y));

which is a syntax error. They aren't required when the variable isn't initialized as part of the my. Also I personally think that they add visual calrity when the reference to the variable is taken. Since the my returns the variable declared (as an lvalue) we can take a reference to it with \. The reference operator \ can technically go inside the parens or outside in this case as

\($x,$y,$z)

is shorthand for

(\$x,\$y,\$z)

Hope that clarifys things. ;-) Er, and yes. You analysed it correctly. :-)

A couple of related tricks are:

my $txt="Foo bar"; (my $clean=$txt)=~s/oo/u/g; open my $fh,"File" or die "File $!"; if (my ($x,$y,$z)=/A(..)(..)(..)Z/) { }

---
demerphq


Replies are listed 'Best First'.
Re^3: GetOpt::Long usage style
by OneTrueDabe (Acolyte) on May 08, 2014 at 16:00 UTC

    I know this is ancient, but since it's high on the Google hit list, I wanted to mention one thing...

    This very cool trick does not work for @arrays. :-(

    This:

    use Getopt::Long; GetOptions( 'single=s' => \(my $single = ''), 'multi=s' => \(my @multi = ()), );
    does *NOT* DWIM. According to "perlref":
    As a special case, "\(@foo)" returns a list of references to the contents of @foo, not a reference to @foo itself.
    I tried all kinds of permutations, and the best I could come up with was:
    use Getopt::Long; GetOptions( 'single=s' => \(my $single = ''), 'multi=s' => do { use vars '@multi'; \@multi }, );
    which, isn't quite as clean, IMHO.

    (It *DOES*, however, keep the variable declarations and command-line options on the same line, at least, so you don't have to make changes in multiple places when adding new options. *shrug*)

      use Getopt::Long; GetOptions( 'single=s' => \(my $single = ''), 'multi=s' => \my @multi, );

      If you want to provide a non-empty default value, one way is:

      use Getopt::Long; GetOptions( 'single=s' => \(my $single = ''), 'multi=s' => grep { @$_ = ('a','b') } \my @multi, );

      - tye        

      Besides what tye said in Re^4: GetOpt::Long usage style (\my @a), you can just use an arrayref instead. Obviously the reference operator \ required for scalars can be omitted.

      'multi=s' => (my $multi = [1..3]),

      Same for a hash/hashref. Admittedly it is not quite the same as what one would expect from

      'multi=s' => (\my @multi = (1..3)),

      Which throws an error, which I think is arguably an error in Perl.

      BTW, sorry it took me so long to reply, and thanks for adding your point.

      ---
      $world=~s/war/peace/g

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