FILE test

Ruby
1

I noticed that a lot of scripts apply the following coding pattern:

if FILE == $0
…
end

I know what is does but what kind of problems does it solve?

thx,

used-to-be-a-Smalltalker

2

On Feb 21, 2006, at 8:58 AM, raving_ruby_rider wrote:

I noticed that a lot of scripts apply the following coding pattern:

if FILE == $0
…
end

I know what is does but what kind of problems does it solve?

It allows the file to be both a library (when required the if
statement will not run) and executable.

Hope that helps.

James Edward G. II

3

You will see this sort of thing in other scripting languages. FILE
contains the name of the file source file and $0 is the name of the
currently executing script. So a file called hello.rb

class Hello
def initialize(name)
@name = name
end

def greet
    puts "Hello #{@name}"
end

end

if FILE == $0 then
h = Hello.new(‘World’)
h.greet
end

you can then run this file with ruby hello.rb which will run the code at
the bottom. However with tom.rb

require ‘hello’

h = Hello.new(‘tom’)
h.greet

when you run tom.rb the FILE == $0 part of hello does not run as the
file hello.rb but the currently executing script is tom.rb. This allows
you to have a ruby file hold the class for inclusion by other scripts
and also be a utility script in it’s own right.

4

DÅ?a Utorok 21 Február 2006 20:25 Damphyr napísal:

and also be a utility script in it’s own right.

Not to mention the fact that it allows you to easily write unit tests
for most of the code in a script.

Which I personally can’t bear the sight of. Library is script is test?
Nuh-uh.
Just my two cents.

David V.

5

On 2/21/06, David V. [email protected] wrote:

Which I personally can’t bear the sight of. Library is script is test? Nuh-uh.

So what is the ‘ruby way’ to store your unit tests? A separate
require’d file?

6

Peter H. wrote:

You will see this sort of thing in other scripting languages. FILE
contains the name of the file source file and $0 is the name of the
currently executing script. So a file called hello.rb

…

when you run tom.rb the FILE == $0 part of hello does not run as the
file hello.rb but the currently executing script is tom.rb. This allows
you to have a ruby file hold the class for inclusion by other scripts
and also be a utility script in it’s own right.

Not to mention the fact that it allows you to easily write unit tests
for most of the code in a script.
V.-

–
http://www.braveworld.net/riva

7

Adam S. wrote:

So what is the ‘ruby way’ to store your unit tests? A separate
require’d file?

Well, going by the Pickaxe book you end up with something like this:

./classfilename
->/doc
->/lib
->/test

in ./classfilename/lib you create your ruby source file classfilename.rb
in ./classfilename/test you create your ruby test/unit file
classfilename_tc.rb

In classfilename_tc.rb you put the following lines at the start:

#----------------------------------------------------------------

The following prefixes …/lib to the active ruby load path

$:.unshift File.join(File.dirname(FILE), “…”, “lib”)

require ‘test/unit’
require ‘classfilename’

class Test_ClassFileName < Test::Unit::TestCase
…
#----------------------------------------------------------------

and then write your test cases as methods. When you run your test suite
you can invoke it from any palce on the system as the #unshift prefixes
the load path with the relative location of the classfilename.rb with
respect to the test case file.

Thus, assuming that for the example given above that ./ = ~/ruby then:

#ruby -w ~/ruby/classfilename/test/classfilename_tc.rb

will work whatever pwd you are in.

I love test/unit…

Regards,
Jim

8

David V. wrote:

and also be a utility script in it’s own right.
Not to mention the fact that it allows you to easily write unit tests
for most of the code in a script.

Which I personally can’t bear the sight of. Library is script is test? Nuh-uh.
Just my two cents.
Well I actually put the unit tests in a different file.
The if $0==FILE check allows me to require the script in the unit
test file.
Following mostly the DRY principle and having a knack for organizing
code allows you to group most of the functionality in objects (at which
point you put them in a ‘library’ file and forget about it) or methods
to be used by the ‘top-level’ script. Requiring the ‘script’ file allows
me to unit test the methods without contriving manual tests.
I found it most valuable when I do parameter parsing and
parameter/configuration validation in my command line scripts.
Cheers,
V.-

–
http://www.braveworld.net/riva