[Tutorial] Introduction to Perl's awesomeness (IV)

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Script arguments

A Perl script can receive arguments from the user as well. In Perl I always prefer passing arguments than asking user for manual input. This is due to the fact that I use Perl for scripting, thus I want to automate the task: launch it and it does the work, not have it wait for my input.

A Perl script receives the arguments from the OS in the @ARGV array (and yet another C-like thing ). The first element $ARGV[0] is actually the first argument, and not the script name (C users will understand why I'm taking about this).

So for example, a script that computes the addition of 2 numbers:

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#!/usr/bin/perl

use strict;

my $sum = $ARGV[0] + $ARGV[1];
print("$ARGV[0] + $ARGV[1] = $sum\n");

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> perl sum.pl 6 4
6 + 4 = 10

Water can flow... or it can crash!

Perl flow control structres are the same than on C. Boolean operators are the same than on C, too (although there are more word-ish alternatives, like "and" instead of "&&"...).

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if(condition)
{
}
elsif (condition)
{
}
else
{
}

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while(condition)
{
}

do
{
} while (condition)

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for(initialization; stop_condition; iteration_operation)
{
}

for $variable (@array)
{
}

The for $variable (@array) loop will go through all array elements, while $variable will take one element value in each iteration. To show an example:

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#!/usr/bin/perl

use strict;

my @array_example = (0, 1, 2, 3, 4, 5, 6, 7, 8, 9);

for my $number (@array_example)
{
	print("$number\n");
}

The $variable can be removed, in which case the default scalar $_ will hold the value:

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#!/usr/bin/perl

use strict;

my @array_example = (0, 1, 2, 3, 4, 5, 6, 7, 8, 9);

for (@array_example)
{
	print("$_\n");
}

Comparison operators

(numbers)

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==		Equal
!=		Not equal
>=		Greater or equal
>		Greater
<		Lesser
<=		Lesser or equal

(strings)

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eq		Equal
ne		Not equal
gt		Greater than
lt		Lesser than

Logic operators

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!	Not
&&	And
||	Or
^	Exclusive or (Xor)

Let's expand our last addition script into adding any list of numbers passed as arguments:

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#!/usr/bin/perl

use strict;

my $total = 0;
my $print;
for (@ARGV)
{	
	$print .= "$_+";
	$total += $_;
}
chop($print);
print("$print = $total\n");

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> ./sum.pl 6 5 6 12 12.5
6+5+6+12+12.5 = 41.5

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