Linux Admin - Set Up Perl for CentOS Linux

 Perl has been around for a long time. It was originally designed as a reporting language used for parsing text files. With increased popularity, Perl has added a module support or CPAN, sockets, threading, and other features needed in a powerful scripting language.

The biggest advantage of Perl over PHP, Python, or Ruby is: it gets things done with minimal fuss. This philosophy of Perl does not always mean it gets things done the right way. However, for administration tasks on Linux, Perl is considered as the go-to choice for a scripting language.

Some advantages of Perl over Python or Ruby are −

• Powerful text processing

• Perl makes writing scripts quick and dirty (usually a Perl script will be several dozen lines shorter than an equivalent in Python or Ruby)

• Perl can do anything (almost)

Some drawbacks of Perl are −

• Syntax can be confusing

• Coding style in Perl can be unique and bog down collaboration

• Perl is not really Object Oriented

• Typically, there isn't a lot of thought put into standardization and best-practice when Perl is used.

When deciding whether to use Perl, Python or PHP; the following questions should be asked −

• Will this application ever need versioning?
• Will other people ever need to modify the code?
• Will other people need to use this application?
• Will this application ever be used on another machine or CPU architecture?

If the answers to all the above are "no", Perl is a good choice and may speed things up in terms of end-results.

With this mentioned, let's configure our CentOS server to use the most recent version of Perl.

Before installing Perl, we need to understand the support for Perl. Officially, Perl is only supported far back as the last two stable versions. So, we want to be sure to keep our development environment isolated from the CentOS version.

The reason for isolation is: if someone releases a tool in Perl to the CentOS community, more than likely it will be modified to work on Perl as shipped with CentOS. However, we also want to have the latest version installed for development purposes. Like Python, CentOS ships Perl focused on the reliability and not cutting edge.

Let's check our current version of Perl on CentOS 7.

[root@CentOS]# perl -v 
This is perl 5, version 16, subversion 3 (v5.16.3) built for x86_64-linux-thread-multi

We are currently running Perl 5.16.3. The most current version as of this writing is: perl-5.24.0

We definitely want to upgrade our version, being able to use up-to-date Perl modules in our code. Fortunately, there is a great tool for maintaining Perl environments and keeping our CentOS version of Perl isolated. It is called perlbrew.

Let's install Perl Brew.

[root@CentOS]# curl -L https://install.perlbrew.pl | bash 
% Total    % Received % Xferd  Average Speed   Time    Time     Time  Current 
                             Dload  Upload   Total   Spent    Left  Speed 
100   170  100   170    0     0    396      0 --:--:-- --:--:-- --:--:--   397 
100  1247  100  1247    0     0   1929      0 --:--:-- --:--:-- --:--:--  1929

Now that we have Perl Brew installed, let's make an environment for the latest version of Perl.

First, we will need the currently installed version of Perl to bootstrap the perlbrew install. Thus, let's get some needed Perl modules from the CentOS repository.

Note − When available we always want to use CentOS Perl modules versus CPAN with our CentOS Perl installation.

Step 1 − Install CentOS Perl Make::Maker module.

[root@CentOS]# yum -y install perl-ExtUtils-MakeMaker.noarch

Step 2 − Install the latest version of perl.

[root@CentOS build]# source ~/perl5/perlbrew/etc/bashrc
[root@CentOS build]# perlbrew install -n -j4 --threads perl-5.24.1

The options we chose for our Perl install are −

• n − No tests

• j4 − Execute 4 threads in parallel for the installation routines (we are using a quadcore CPU)

• threads − Enable threading support for Perl

After our installation has been performed successfully, let's switch to our newest Perl environment.

[root@CentOS]# ~/perl5/perlbrew/bin/perlbrew use perl-5.24.1

A sub-shell is launched with perl-5.24.1 as the activated perl. Run 'exit' to finish it.

[root@CentOS]# perl -v

This is perl 5, version 24, subversion 1 (v5.24.1) built for x86_64-linuxthread-multi

(with 1 registered patch, see perl -V for more detail)

Copyright 1987-2017, Larry Wall

Perl may be copied only under the terms of either the Artistic License or the GNU General
Public License, which may be found in the Perl 5 source kit.

Complete documentation for Perl, including FAQ lists, should be found on this system 
using "man perl" or "perldoc perl".  If you have access to the Internet, point your 
browser at http://www.perl.org/, the Perl Home Page.

[root@CentOS]#

Simple perl script printing perl version running within the context of our perlbrew environment −

[root@CentOS]# cat ./ver.pl  
#!/usr/bin/perl
print $^V . "\n";

[root@CentOS]# perl ./ver.pl  
v5.24.1 
[root@CentOS]#

Once perl is installed, we can load cpan modules with perl brew's cpanm −

[root@CentOS]# perl-brew install-cpanm

Now let's use the cpanm installer to make the LWP module with our current Perl version of 5.24.1 in perl brew.

Step 1 − Switch to the context of our current Perl version.

[root@CentOS ~]# ~/perl5/perlbrew/bin/perlbrew use perl-5.24.1

A sub-shell is launched with perl-5.24.1 as the activated perl. Run 'exit' to finish it.

[root@CentOS ~]#

Step 2 − Install LWP User Agent Perl Module.

[root@CentOS ~]# ~/perl5/perlbrew/bin/cpanm -i LWP::UserAgent

Step 3 − Now let's test our Perl environment with the new CPAN module.

[root@CentOS ~]# cat ./get_header.pl  
#!/usr/bin/perl 
use LWP; 
my $browser = LWP::UserAgent->new(); 
my $response = $browser->get("http://www.slcc.edu/"); 
unless(!$response->is_success) { 
   print $response->header("Server"); 
}

[root@CentOS ~]# perl ./get_header.pl  
Microsoft-IIS/8.5 [root@CentOS ~]#

There you have it! Perl Brew makes isolating perl environments a snap and can be considered as a best practice as things get with Perl.