On Wed, Aug 4, 2010 at 12:09, Sooraj S <[email protected]> wrote:
> Hi,
>
> My script has 3 options which recieve integers. If any of those
> options are having a value which is less than zero i want to make them
> to 100.
>
> eg: if opt2 = 32 and opt3 = 24 i want to make them to 100.
>
> code
> =====
> our $opt1,$opt2,$opt3;
> our @opt = (\$opt1,\$opt2,\$opt3);
>
> GetOptions('opt1=i' => \$opt1,
> 'opt2=i' => \$opt2,
> 'opt3=i' => \$opt3)
> check();
>
> sub check
> {
> foreach (@opt)
> {
> # error here : The change does not get reflected on the actual
> options.
> if ($$_ < 100)
> {
> $$_ = 100;
> }
> }
> }
Let's go over what this should look like:
#!/usr/bin/perl
use strict;
use warnings;
The standard header all of your scripts should start with. The
[strict pragma][0] will turn off three features of Perl 5 that have
been found to cause coding mistakes when used without proper caution.
The [warnings pragma][1] turns on the printing of optional warnings
that will help you immensely in finding problems with your code.
use Getopt::Long;
This includes the [Getopt::Long module][2] which will read commandline
options from @ARGV for you.
GetOptions(
'opt1=i' => \my $opt1,
'opt2=i' => \my $opt2,
'opt3=i' => \my $opt3,
);
This function call will read the options opt1, opt2, and opt3 from the
commandline and store their values (if any) in the lexical variables
$opt1, $opt2, and $opt3.
check($opt1, $opt2, $opt3);
This calls the function check with the three arguments we parsed from
the commandline.
print
"opt1: $opt1\n",
"opt2: $opt2\n",
"opt3: $opt3\n";
This prints out the three option's values after the call to check.
sub check {
This starts the definition of the check function.
for my $num (@_) {
}
This [for loop][3] will iterate over the arguments passed to check and
alias $num to them. Because $num is aliased to the the elements of @_
and the elements of @_ are [aliased to the arguments passed to
check][4], any changes you make to $num will change the corresponding
variable passed to check. Note that I am using the keyword for
instead of foreach. Perl 5 does not care which keyword you use, and
for is four characters shorter. Perl 5 can easily determine if your
for loop is an iterating loop (like this one) or a C-style
(initialize; test; mutate) loop based on the contents of the
parenthesis.
unless (defined $num and $num > 99) {
$num = 100
}
This will set $num to 100 [unless]5] $num is [defined][6] and greater
than 99. If the user does not pass an argument, the corresponding
variable will not be initialized. Trying to use a variable that has
not initialized is [considered to be a mistake][7] by the warnings
pragma, so we check to make sure that is defined before we attempt to
compare it with 99. The short-circuit nature of [and][8] makes sure
that we do not do the comparison if $num is undefined.
Putting it all together we get:
#!/usr/bin/perl
use strict;
use warnings;
use Getopt::Long;
GetOptions(
'opt1=i' => \my $opt1,
'opt2=i' => \my $opt2,
'opt3=i' => \my $opt3,
);
check($opt1, $opt2, $opt3);
print
"opt1: $opt1\n",
"opt2: $opt2\n",
"opt3: $opt3\n";
sub check {
for my $num (@_) {
unless (defined $num and $num > 99) {
$num = 100
}
}
}
[0]: http://perldoc.perl.org/strict.html
[1]: http://perldoc.perl.org/warnings.html
[2]: http://perldoc.perl.org/Getopt/Long.html
[3]: http://perldoc.perl.org/perlsyn.html#Foreach-Loops
[4]: http://perldoc.perl.org/perlsub.html#DESCRIPTION
[5]: http://perldoc.perl.org/perlsyn.html#Compound-Statements
[6]: http://perldoc.perl.org/functions/defined.html
[7]: http://perldoc.perl.org/perldiag.html#Use-of-uninitialized-value%25s
[8]: http://perldoc.perl.org/perlop.html#Logical-And
--
Chas. Owens
wonkden.net
The most important skill a programmer can have is the ability to read.
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