Hi.
The easiest way is to use the Getopt::Std module ( it is part of the standard distribution ). Here is a sample program.

#!/usr/bin/perl -w

use strict;
use Getopt::Std;
use vars qw( $opt_s $opt_r $opt_n );

if( ! getopts('srn' ) )
{
  die "Usage: filename.pl -srn filename\n";
  #Example: perl myfile.pl -r test.txt
}

my @file = <>;

if( $opt_s )
{
  @file = sort { $a cmp $b } @file;
}

if( $opt_r )
{
  @file = reverse @file;
}

if( $opt_n ) 
{
  @file = sort { $a <=> $b } @file;
}
[download]

Each command-line switch is assigned to its respective scalar variable ( $opt_s, etc. ) and if it exists, its individual value is 1.
You can also use multiple switches:

$perl myfile.pl -rn test.txt
# Reverse the contents of test.txt and perform
# a numeric sort on it.
[download]

# Sample runs:

C:\perl>perl pg8.pl -r test.txt

third line.
second line.
first line.

C:\perl>

C:\perl>perl pg8.pl -n test.txt
2
33
33
44
48
55
889
990

C:\perl>
 
C:\perl>perl pg8.pl -c test.txt
Unknown option: c
Usage: filename.pl -srn filename

C:\perl>
[download]

In the last example, I hadn't declared an $opt_c in the line 'use vars qw ( $opt_s ... );' or an if() statement to handle it. This is why I received the message.

Hope this helps,
-Katie.

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