Reduce Redundant Repetition

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

The following chunk facilitates default values for command-line arguments. It works fine, but I suspect there's a less redundant approach than just repeating "if defined($opt_foo){$foo=$opt_foo} else {$foo=def_val}" for seven different values of "foo". I'd use hash keys and values, but there are three unique parameters for each iteration.

Suggestions, o wise brethren and sistren?

#!/usr/bin/perl -w

use strict;
use Getopt::Long

my (
  $targ,       $opt_targ,
  $firstport,  $opt_firstport,
  $lastport,   $opt_lastport,
  $proto,      $opt_proto,
  $udptimeout, $opt_udptimeout,
  $contimeout, $opt_contimeout,
  $help,
);

GetOptions(
  'targ=s'       => \$opt_targ,
  'firstport=s'  => \$opt_firstport,
  'lastport=s'   => \$opt_lastport,
  'proto=s'      => \$opt_proto,
  'udptimeout=s' => \$opt_udptimeout,
  'contimeout=s' => \$opt_contimeout,
  'help!'        => \$opt_help,
);
if (defined $opt_targ){ $targ = $opt_targ }
  else {$targ='localhost';}

if (defined $opt_firstport){ $firstport = $opt_firstport }
  else {$firstport=1;}

if (defined $opt_lastport){ $lastport = $opt_lastport }
  else {$lastport=1024;}

if (defined $opt_proto){ $proto = $opt_proto}
  else {$proto='tcp';}

if (defined $opt_udptimeout){ $udptimeout = $opt_udptimeout }
  else {$udptimeout=3;}

if (defined $opt_contimeout){ $contimeout = $opt_contimeout }
  else {$contimeout=3;}

if (defined $opt_help){
  Usage('You rang, sir?');
  exit;
}
[download]

    cheers,
    Don
    striving toward Perl Adept
    (it's pronounced "why-bick")

Comment on Reduce Redundant Repetition Download Code

Replies are listed 'Best First'.
(jcwren) Re: Reduce Redundant Repetition by jcwren (Prior) on Jan 21, 2002 at 21:21 UTC
How about: `$proto = defined $opt_proto ? $opt_proto : 'tcp'` Personally, though, I'd go for putting all your arguments in a hash, with a reference to the opt_arg value, the variable you want the final result in, and the default value, and use a for loop to rip through them setting them all. Perhaps include a type (numeric, string, flag) and do a little type checking. For instance, if someone passed '123' to the $opt_tcp value, it prolly ain't gonna work... --Chris e-mail jcwren	[reply] [d/l]
Re: Reduce Redundant Repetition by kal (Hermit) on Jan 21, 2002 at 21:38 UTC
There are a number of ways to reduce some of this. The easiest way to get rid of the if's is probably something like: `$contimeout = $opt_contimeout \|\| 3;` Another simple way of setting defaults is to set them up before using Getopt::Long: `#!/usr/bin/perl -w use strict; use Getopt::Long; my ($lines, $cols) = (5, 16); GetOptions ('line=s' => \$lines, 'col=s' => \$cols); print "Lines: $lines Cols: $cols\n";` [download] A very simple example I know, but it illustrates the point :) Update: jcwren pointed out that I failed to mention this has a potential failure if you use '\|\|' - if you want to set a value to '0', you won't be able to unless the default is also '0'. I advise pre-setting the defaults, and then letting the user override them - much simpler :) Thanks, jcwren.	[reply] [d/l] [select]
(tye)Re: Reduce Redundant Repetition by tye (Sage) on Jan 21, 2002 at 22:08 UTC
Until Perl 6, you might find def -- Deal nicely with undefined values useful. `$targ= def( $opt_targ, 'localhost' );` - tye (but my friends call me "Tye")	[reply] [d/l]
Re: Reduce Redundant Repetition (Rus: use ternaries) by Russ (Deacon) on Jan 22, 2002 at 00:08 UTC
I don't see anyone using the ternary operator... `$targ = defined $opt_targ ? $opt_targ : 'localhost'; $firstport = defined $opt_firstport ? $opt_firstport : 1; $lastport = defined $opt_lastport ? $opt_lastport : 1024; $proto = defined $opt_proto ? $opt_proto : 'tcp'; $udptimeout = defined $opt_udptimeout ? $opt_udptimeout : 3; $contimeout = defined $opt_contimeout ? $opt_contimeout : 3; Usage('<lurch>You rang?</lurch>'), exit if defined $opt_help;` [download] And it still works with valid zero values. Russ	[reply] [d/l]
Re: Reduce Redundant Repetition by mrbbking (Hermit) on Jan 21, 2002 at 23:15 UTC
You might consider replacing something like this... `if (defined $opt_targ){ $targ = $opt_targ } else {$targ='localhost';}` [download] with something like this... `$targ = $opt_arg; $targ \|\|= 'localhost';` [download] ...following the "this breaks if zero is an acceptable value" admonition previously stated above...	[reply] [d/l] [select]
Re: Reduce Redundant Repetition by Aristotle (Chancellor) on Jan 22, 2002 at 03:27 UTC
A demonstration is better than many words: `#!/usr/bin/perl -w use strict; use Getopt::Long; my $targ = 'localhost'; my $firstport = 1; my $lastport = 1024; my $proto = 'tcp'; my $udptimeout = 3; my $contimeout = 3; { my %options; GetOptions(\%options, qw(targ=s firstport=s lastport=s proto=s udpti +meout=s contimeout=s help!)); if (defined $options{help}){ Usage('You rang, sir?'); exit; } ($targ, $firstport, $lastport, $proto, $udptimeout, $contimeout) = @options{qw(targ firstport lastport proto udptimeout contimeout)}; }` [download] With some further generalization the variable-/option-names wouldn't have to appear four times each as in this code either. Update: maybe you want `qw(targ=s firstport=s lastport=s proto=s udptimeout=i contimeout=i help!)`? I can see someone saying `POP3` for the port f.ex - but it doesn't seem to make any sense to take arbitrary values for the timeout parameters. Makeshifts last the longest.	[reply] [d/l]