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

Greetings,

I was studying someone else's code and came across this line: 

GetOptions(
"refresh=i" => \ (my $REFRESH = 10),
...other option variables...
  );

[download]

I'm confused by the syntax of this line. It is nowhere to be found in the module documentation. According to the module, the "=" sign in "refresh=i" makes the option mandatory in the command line. So if that's the case, why does the argument above appear to be assigning a value to "$REFRESH"?

Respectfully Yours,

$PM = "Perl Monk's";
$MCF = "Most Clueless Friar Abbot";
$nysus = $PM . $MCF;

Replies are listed 'Best First'.
Re: "Getoptions'" argument syntax
by wog (Curate) on Jun 15, 2001 at 23:36 UTC
    That code is another way of saying: 

    my $REFRESH = 10;
GetOptions(
"refresh=i" => \$REFRESH,
......
);

    [download]

    You can think of the my as both representing and declaring the lexical variable(s) in question.

    update: The reason it's a =i and not a :i is that the =i makes the number mandatory after the option, but not the option.

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      OK, thanks. But still, if $REFRESH is required to be given a value from command line, why bother setting it to 10? Why not make the command optional with a ":". This is merlyn's code so I'm assuming a guru like that would have some logic behind this but maybe I'm wrong.

      $PM = "Perl Monk's";
      $MCF = "Most Clueless Friar Abbot";
      $nysus = $PM . $MCF;

[reply]
        '=' means that: *If* you give the option you *must*(mandatory) give an argument. To give the option although is *optional*. ':' means you can give the option with or without an argument.
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Re: "Getoptions'" argument syntax
by btrott (Parson) on Jun 16, 2001 at 00:15 UTC
    The '=' in 'refresh=i' doesn't mean that 'refresh' is a mandatory option to the program. It means that, if 'refresh' is supplied, the *integer argument* is mandatory. So you can't just have 
        $ foo.pl --refresh

    [download]
    An argument to 'refresh' is mandatory.

    I don't think there *is* a way to indicate that an option is mandatory (ie. that 'refresh' must be provided as an option).

    And since 'refresh' may not be provided, the 

        $REFRESH = 10

    [download]
    sets the default value for 'refresh' to 10. And it can be overriden on the command line with '--refresh'.
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Re: "Getoptions'" argument syntax
by mikfire (Deacon) on Jun 16, 2001 at 00:08 UTC 
    borris)cat getopt.pl

#!usr/bin/perl -w

use Getopt::Long;
use strict;

GetOptions( "refresh=i", \ (my $refresh = 10 ) );

print "refresh = $refresh\n";

borris)perl getopt.pl
refresh = 10
borris)perl getopt.pl -refresh 5
refresh = 5

    [download]
    Quick experimentation suggests that it provides a default value for an optional parameter. Which is really quite neat, and seems to be completely undocumented.

    mikfire

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[d/l]
      ... seems to be completely undocumented.

      Getopt::Long's documentation does document it, though not directly (emphasis added):

      The call to GetOptions() parses the command line arguments that are present in "@ARGV" and sets the option variable to the value "1" if the option did occur on the command line. Otherwise, the option variable is not touched.
      It's just a little leap from that that you can take advantage of having an option's variable set before its passed to GetOptions, which is what the odd code given does.

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