Answer:

If you know Perl well, there is no need to use awk to do string processing such as string splitting, it is easy with Perl also, e.g.

# echo "foo,bar,k3"  | perl -F',' -lane 'print $F[1]'
bar

Answer:

To print a string of "Hello World" to the standard output in different scripting languages

1. Perl

print "Hello, World!";

2. Python

print('Hello, World!')

3. PHP

echo "Hello, World!";

4. Ruby

puts "Hello, World!"

Answer:

In Perl, you can enforce using the strict mode to reduce the chance of nasty error, e.g.

$foo = 'bar';
print $foo;

If you run the above problem, it is completely valid.

# perl test.pl
bar

However, if you use the strict pragma

use strict;

$foo = 'bar';
print $foo;

And run the program again..

# perl test.pl
Global symbol "$foo" requires explicit package name at test.pl line 3.
Global symbol "$foo" requires explicit package name at test.pl line 4.
Execution of test.pl aborted due to compilation errors.

Since the $foo is not declared before the first use, so the compilation stopped. In modern Perl developements, it is recommended to alwasys use the strict pragma in order to write a better and maintainable program.

To fix the problem, you need to use the my keyword, e.g.

use strict;

my $foo = 'bar';
print $foo;

And run the program again. (Thanks Jeroen for the suggestion)

Answer:

To assign a multi-line string to a variable in Perl, is easy with the following trick:

my $html = <<END;
<p>
    This is HTML content.
</p>

END

print $html;

Answer:

To find the current package in your Perl script, you can try something like the following:

package Foo;

my $current_package = __PACKAGE__;
print "I am in package $current_package\n";

1;

When executed:

# perl foo.pl

I am in package Foo

Answer:

Perl does not support multi-line comments like C++ or Java. If you want to comment out a large block of Perl code, there is still a trick.

package Foo;

=pod
This is a multi-line comments 
more...
more...
=cut

print "Hello";

Answer:

For example, we want to know where the module JSON and related modules exist in the local file system, we can try:

# perl -MJSON -e'print $_ . " => " . $INC{$_} . "\n" for keys %INC'

attributes.pm => /usr/share/perl/5.10/attributes.pm
XSLoader.pm => /usr/local/lib/perl/5.10.0/XSLoader.pm
warnings/register.pm => /usr/share/perl/5.10/warnings/register.pm
Carp.pm => /usr/share/perl/5.10/Carp.pm
Exporter/Heavy.pm => /usr/share/perl/5.10/Exporter/Heavy.pm
common/sense.pm => /usr/local/share/perl/5.10.0/common/sense.pm
vars.pm => /usr/share/perl/5.10/vars.pm
Exporter.pm => /usr/share/perl/5.10/Exporter.pm
strict.pm => /usr/share/perl/5.10/strict.pm
constant.pm => /usr/local/share/perl/5.10.0/constant.pm
warnings.pm => /usr/share/perl/5.10/warnings.pm
JSON/XS.pm => /usr/local/lib/perl/5.10.0/JSON/XS.pm
overload.pm => /usr/share/perl/5.10/overload.pm
base.pm => /usr/share/perl/5.10/base.pm
JSON.pm => /usr/local/share/perl/5.10.0/JSON.pm

Answer:

The full list of Ubuntu's managed Perl modules is here (for lucid): http://packages.ubuntu.com/lucid/perl/

You can use apt-get into install those modules, instead of CPAN. The advantage is you can remove them easier with the apt-get command, while for CPAN, you need to do it manually.

Answer:

To write to the middle of a text file, can be easily performed by Perl.

Assume the file has 10 lines, you want to replace the 5th line:

#!/usr/bin/perl
use strict;
use Tie::File;

my $file = 'foo.txt';

tie @array, 'Tie::File', $file or die "Cannot open $file \n";

@array[4] = "Replaced!\n";

That's easy?

Answer:

In Perl, sometimes you can use both `||` and `or` to to do the same thing. But the main different is:

• or has very low precedence, which is useful for flow control

Example:

open FILE,  $file or die("Cannot open $file");   # Work
open FILE,  $file || die("Cannot open $file");   # Does not work , because it it same as the next statement
open FILE, ($file || die("Cannot open $file"));  # Obviously not work