Your generator cannot generate a password with the letters a, b or c due to the +3 when selecting the random letter. See rand, which already returns a number in the range from 0..$len.

The variable $len is named wrong - it has the last index of @lett, not the number of elements in the array. This means that your password generator would never output the last element from @lett if it weren't for the + 3 from the previous step. I would use:

$len = @lett;
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... which assigns to $len the number of elements in @lett.

Other than that, using double quotes in a simple assignment is weird unless you have a special reason to do so - and if you are starting with Perl just now, those special reasons ("stringification") are still far away. So, no assignment should be of the form

    $foo = "$bar";
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and always of the form

    $foo = $bar;
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Thanks.
The use of "$.." comes from the bash programming.
Thinking about what you said made me realize that, indeed, the +3 is more damage than else.
-- Luca Francesca <luca.francesca@ciscoland.eu> SysAdmin/Integrator @ Vodafone Italy & Ntt Data

Hello cisco88, and welcome to the Monastery!

In addition to the excellent points made by Corion...

It’s always a good idea to:

use strict;
use warnings;
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in any Perl script. For one-liners, you can do:

perl -Mstrict -we ...
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to get the same benefit. In this case, warnings would have given you messages of the form:

Use of uninitialized value in print...
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which arise because the expression rand($len) % $len + 3 sometimes generates array indexes beyond the end of the @lett array.

Get in the habit of always using strict and warnings now, and you will save yourself a lot of time and grief in the future!

Hope that helps,

Thanks for the tips and the welcome.
Il surely use them. The more I can fix at firts writing, the better it is :)
-- Luca Francesca
<luca.francesca@ciscoland.eu>

SysAdmin/Integrator
@
Vodafone Italy & Ntt Data

It looks like you're trying to get a 20-character random password generated using the characters from 'a' through 'z'. Here's a solution that uses Bytes::Random::Secure:

perl -MBytes::Random::Secure=random_string_from -E 'say random_string_
+from( join("", "a" .. "z" ), 20 );'
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Bytes::Random::Secure uses Math::Random::ISAAC as the Random Number Generator, and relies on Crypt::Random::Source to generate a strong seed for the ISAAC generator. The random_string_from function takes care to be free from modulo bias regardless of source string length.

The current release of Bytes::Random::Secure on CPAN has a sort of hefty dependency chain due to its use of Crypt::Random::Source. The next release (due out in a few days) will replace Crypt::Random::Source with Dana Jacobsen's new Crypt::Random::Seed, which is designed to some degree with Bytes::Random::Secure in mind. It has core-only dependencies, provides better fall-backs and portability than Crypt::Random::Source. The next version of Bytes::Random::Secure (watch for v0.20) will also provide an OO interface alongside the functions interface for times when the user requires more control over how ISAAC is seeded.

Thanks :)

-- Luca Francesca
<luca.francesca@ciscoland.eu>
SysAdmin/Integrator
@
Vodafone Italy & Ntt Data

Just a variation on this theme using the buildin features:

#!/usr/bin/perl                                                       
+                                            

use strict;
use warnings;

my ( @l, @u, @n, @s, @p, $i, $j );

open( URANDOM, "</dev/urandom" ) || die $!;
read( URANDOM, $_, 4 );
close URANDOM;

srand( unpack( "L", $_ ) );

@l = ( "a" .. "z" );
@u = ( "A" .. "Z" );
# @n = ( 0 .. 9 );                                                    
+                                            
# @s = (                                                              
+                                            
#     '#', ',', ' ',                                                  
+                                            
#     qw( ! " $ % & ' ( ) * +  - . / : ; < = > ? @ [ \ ] ^ _ ` { | } ~
+ )                                          
# );                                                                  
+                                            

push( @p, splice( @l, int( rand(@l) ), 1 ) ) for ( 1 .. 10 );
push( @p, splice( @u, int( rand(@u) ), 1 ) ) for ( 1 .. 10 );
# push( @p, splice( @l, int( rand(@l) ), 1 ) ) for ( 1 .. 3 );        
+                                            
# push( @p, splice( @u, int( rand(@u) ), 1 ) ) for ( 1 .. 3 );        
+                                            
# push( @p, splice( @n, int( rand(@n) ), 1 ) ) for ( 1 .. 2 );        
+                                            
# push( @p, splice( @s, int( rand(@s) ), 1 ) ) for ( 1 .. 2 );        
+                                            

for ( $i = @p ; --$i ; ) {
    $j = int( rand( $i + 1 ) );
    next if $i == $j;
    @p[ $i, $j ] = @p[ $j, $i ];
}

print join( "", @p ) . qq(\n);

__END__
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Regards, Karl