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

I am using Getopts to pull some command line switches. I have one optional switch, -l, that when used requires an argument. Here's my code: 
$opts = getopts ('uhal:',\%Options);

if ($opts) {

    $print_users = $Options{u};

    $print_all = $Options{a};

    if ($Options{l}) {
        $logfile=$Options{l};
    } else {
        $logfile="$IDEAS_DIR/sec/logs/daemon.$HOSTNAME";
    }

    if ($Options{h}) {
        ShowUsage();
    }

} else {
    ShowUsage() ;    
}

[download]
so you can see that I am using the "l:" spec to Getopts to show a required argument. When the user doesn't present an argument after -l, however, I don't see how to detect that condition (apart from another condition that might cause the Getopts call to raise an error). $Options{l} doesn't seem to get set in this case, so I can't determine for myself that "yeah they did a -l, but did no argument", and Getopts itself doesn't issue any error messages about forgetting a required argument. When the user forgets the -l argument, I'd like to tell them that they forgot it, but I don't see how I can tell without going ahead and parsing @ARGV myself .. and if I do that, why even use Getopts in the first place? Any suggestions?

Replies are listed 'Best First'.
Re: Getopts and required args
by Shendal (Hermit) on Jun 22, 2000 at 20:10 UTC
    Use Getopt::Long.

    Breifly, here's an example of what your code may end up looking like:
    use strict;
use warnings;
use Getopt::Long;
use vars qw($opt_u $opt_h $opt_a $opt_l);

&GetOptions('l=s','u','h','a') || exit 1;

print "Option found: u\n" if ($opt_u);
print "Option found: h\n" if ($opt_h);
print "Option found: a\n" if ($opt_a);
if ($opt_l) {
    print "Option found: l\n";
    print "  with value: $opt_l\n";
} else {
    print "You must specify -l\n";
    exit 1;
}

    [download]
    Note that 'l=s' means that l must be specified with a value, otherwise, GetOptions() fails.

    Hope that helps,
    Shendal
[reply]
[d/l]
      In this example, it appears that -l is a required switch, which it isn't. Or am I reading this wrong? 
      if ($opt_l) {
    print "Option found: l\n";
    print "  with value: $opt_l\n";
} else {
    print "You must specify -l\n";
    exit 1;
}

      [download]
      In other words, not having $opt_l should NOT be an error... only a NULL $opt_l. And in perl, is there a difference?
[reply]
[d/l]
        Well, in my example it is required. I must have misunderstood your question. If you want to require -l to be paired with a value, but not specifying -l is okay, too, try this:

        use strict;
use warnings;
use Getopt::Long;
use vars qw($opt_u $opt_h $opt_a $opt_l);

#Note that l=s says that l requires an option
#   l:s means that it is optional
#   I have chosen the option method here so that
#   I can handle it how I want programatically
&GetOptions('l:s','u','h','a') || exit 1;

print "Option found: u\n" if ($opt_u);
print "Option found: h\n" if ($opt_h);
print "Option found: a\n" if ($opt_a);
if (defined $opt_l) {
    print "Option found: l\n";
    if ($opt_l) {
    print "  with value: $opt_l\n";
    } else {
    print "  No value specified.\n";
    }
}

        [download]
[reply]
[d/l]
Re: Getopts and required args
by takshaka (Friar) on Jun 23, 2000 at 07:04 UTC 
    die "-l requires an argument\n"
   if exists $Options{l} && !defined $Options{l};

    [download]
[reply]
[d/l]
      Sweet. Thanks :) I won't necessarily use "die", because I want to show the user the ShowUsage text, and I don't necessarily want to list a line number from the source. But this is what I was looking for. Thanks!
[reply]
      Uh I already thanked you, but did it before I logged on (I was so anxious to try it..) ... anyway, thanks again from the "official" husker :)
[reply]

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