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Tag: CPAN

Adding style to perl code

Perl has always been my favourite command line and web programming language. There is nothing Perl can't do. The Perl language combined with the large quantities of modules on CPAN (developed by some of the best programmers on the planet) makes it the kitchen sink of programming languages.

I like to make my code as easy to read as possible. Nothing irks me more than a jumble of spaghetti code with indents and curly braces everywhere. I admit that there are times when a solution to a complex problem comes to me, and I become more concerned with getting my ideas down than with following style rules. But after I have my thoughts properly coded, I want to go back and clean things up a bit. That's where perltidy comes in.

What is Perl::Tidy?

Perltidy is a Perl script which indents and reformats Perl scripts to make them easier to read.

The CPAN module, written by Steve Hancock, makes the functionality of the perltidy utility available to other Perl scripts. That means you can write your script for your own Perl-style needs. I prefer to use the utility.

Installation

Installing Perl::Tidy on OS X is relatively easy. Use the sudo command from the Terminal to run the CPAN command line utility. You need to be logged into an account with administrator privileges. This will pull down and install from CPAN, all the necessary code for using perltidy.

Using perltidy

Once the module has been installed (the utility is placed in /usr/bin ), you can use the command line utility just like any command in Terminal. Perltidy has several command line switches to modify its behaviour. The default styling works well enough for me. To use the command line utility, open up a Terminal window and type :~ perltidy -b /path/to/your/code.pl

I used the -b switch to tell perltidy to create a backup of my script before doing its work. I want a copy just in case something goes wrong. Perltidy does its thing and then exits. If errors are found, e.g. a missing curly brace, perltidy will let you know and create an error file that contains more information about the problem.

Perltidy will take this code:

my %var = { name => ‘khurt’, last => ‘williams’, location => ‘Princeton’, height => ‘164cm’, weight => ‘64 kg’ }; foreach my $key ( sort keys %var ) { printif( “%s:%sn”, $key, $var{$key} ); } #this prints the values in the hash

And turn it into this code:

my %var = {
    name     => 'khurt',
    last     => 'williams',
    location => 'Princeton',
    height   => '164cm',
    weight   => '64 kg'
};
foreach my $key ( sort keys %var ) {
    printif( "%s:%sn", $key, $var{$key} );
}    #this prints the values in the hash

Useful perltidy command:

: ~ perltidy -html -pre code.pl

This will create an HTML snippet with only the PRE section to code.pl.html. This is useful when code snippets are formatted for inclusion in a larger web page (such as a blog).

To learn more about perltidy, type "man perltidy" into Terminal to see the manual page. Prepare to be overwhelmed. Perltidy is feature-rich.

User CPAN installation broken

Here is a workaround for a common problem. You do not have root access to perl but want to install perl libraries. Normally the user can use CPAN with local libraries (PERL5LIB). Sometimes CPAN gets comfused and you get an error like this: Your configuration suggests "/root/.cpan" as your CPAN.pm working directory. I could not create this directory due to this error: mkdir /root/.cpan: Permission denied at /data/eva/perl/lib/perl5/site_perl/5.8.0/CPAN.pm line 552 I google around and found this solution:

Execute the following procedure (it worked for me, though I am not sure if all steps are necessary): 1. Create a directory for the perl modules in your HOME $ mkdir ~/perl5lib 2. Create ~/.cpan and ~/.cpan/CPAN directories: $ mkdir ~/.cpan $ mkdir ~/.cpan/CPAN 3. Create a Config.pm for the CPAN module with $CPAN::Config empty $ echo "\$CPAN::Config = {}"> ~/.cpan/CPAN/MyConfig.pm 4. Execute again: $ perl -MCPAN -e shell This time (if all goes well) it will prompt you for the empty fields in $CPAN::Config.