Hi all. After a long time without publish any tech doc, I’m back!.

Today will see how to use Ruby(yes, Ruby) to make our CGI tools. As you already know, CGI’s are traditional written in Perl, but if we check some Ruby’s history we can find next statement:

Ruby takes best of several worlds: Perl, Python and SmallTalk

So if we have best of Perl I think we have powerful CGI’s.

First of all we need to know that just a few free hosting services provide Ruby as an allowed scripting language, but we can always get cheap hosting(I got mine into 1 USD per month). Besides you can use your own webserver.

Suppose that we already configure our webserver to execute CGI programs, so let’s write code!.

Every script that you write into an interpreted language begins with a line like this:

#!/usr/bin/env ruby

which says: hey! run my amazing code with Ruby(this specific case).
Now you can start write your pages in a similar way what you do into PHP, except you have to require an specific library to make the work less painful: cgi(hard to figure out, isn’t?).

#!/usr/bin/env ruby

require 'cgi'

cgi = CGI.new

Last line of code it’s just used to create a new object of class CGI.

Now, as HTTP protocol requires, our script must send the headers to web browser, if we need a custom headers must read some RFC’s and that boring stuff, instead just tell Ruby to send “standard” headers doing:

puts cgi.header

By the way, if we need to print some to the webpage just do like if you print something into terminal, I mean puts, print, printf and a lot of functions which Ruby provides.

At this point your code looks like:

#!/usr/bin/env ruby

require 'cgi'

cgi = CGI.new
puts cgi.header

Now let’s try something more interesting, assume that we got some parameters from a webform, let’s say we asked to user… mmmh, name and email, classic fields in a webform.

In HTML code the form looks like:

<form method="GET" action="myRubyScript.rb">
<label>Name: <input type="text" name="name" /></label>
<br />
<label>Email: <input type="text" name="email" /></label>

If the above form sends data to our script, then we need to catch and do something with it. So do the next thing:

params = cgi.params
name = params["name"][0]
email = params["email"][0]

May you think what if I need to check the existence of some params?, well we can do that:

params = cgi.params
name = params["name"][0] if params.has_key?"name"
email = params["email"][0] if params.has_key?"email"

Nice, isn’t?. But now you can think… Yep, params it’s a Ruby hash(like an associative array in PHP), why are we processing it first like a hash and then like an array?. Well, the answer comes really faster and hits you hard…

What happened if the parameter values are several to the same parameter name?. Well, Ruby can manage that stuff, that’s why Ruby stores an array as a value of a hash. So if someone passes several names like Sheldon, Raj, Leonard and Howard we can access pretty easy:

params = cgi.params
name1 = params["name"][0]
name2 = params["name"][1]
name3 = params["name"][2]

Some of you can ask how Ruby figures out if the request was made by POST method or GET method, well, at this point Ruby takes every request type as the same. But if you wanna look which type of request the client did you can check it like this:

when "GET"
#Do something with GET
when "POST"
#Do POST stuff

So, do you think that Ruby CGI stuff is really hard?.
Please take a look into Ruby CGI Library Documentation

Greets folks!

[UPDATE] Thanks to Dave B for the corrections. 😀


2 responses »

  1. […] If you dont know how to make a basic CGI app in Ruby, please read this. […]

  2. Dave B says:

    Thanks for this DW – helpful.

    You need …


    Environment variables are in Ruby constant ENV and there’s a missing trailing apostrophe in your example.

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