I'm new to Ruby, so apologies if this sounds really silly.
I can't seem to figure out how to write a "main" code and have methods in the same file (similar to C). I end up with a "main" file which loads a seperate file that has all the methods. I appreciate any guidance on this.
I spotted the following SO post but I don't understand it: Should I define a main method in my ruby scripts?
While it's not a big deal, it's just easier being able to see all the relevant code in the same file. Thank you.
[-EDIT-]
Thanks to everyone who responded - turns out you just need to define all the methods above the code. An example is below:
def callTest1
puts "in test 1"
end
def callTest2
puts "in test 2"
end
callTest1
callTest2
I think this makes sense as Ruby needs to know all methods beforehand. This is unlike C where there is a header file which clearly list the available functions and therefore, can define them beneath the main() function
Again, thanks to everyone who responded.
If you wish to run Ruby scripts like C compiled files, do the following:
and then
chmod a+x file_name.rb
. Everything that is below the first line will be run, as if it was contents ofmain
in C. Of course class and function definitions won't give you any results until they are instantiated/invoked (although the code inside class definitions is actually evaluated, so you could get some output but this is not expected in normal circumstances).There is no magic main function in Ruby. See http://en.wikipedia.org/wiki/Main_function#Ruby
@Hauleth's answer is correct: there is no
main
method or structure in Ruby. I just want to provide a slightly different view here along with some explanation.When you execute
ruby somefile.rb
, Ruby executes all of the code insomefile.rb
. So if you have a very small project and want it to be self-contained in a single file, there's absolutely nothing wrong with doing something like this:It's not that the first two blocks aren't executed, it's just that you don't see the effects until you actually use the corresponding class/method.
The
if __FILE__ == $0
bit is just a way to block off code that you only want to run if this file is being run directly from the command line.__FILE__
is the name of the current file,$0
is the command that was executed by the shell (though it's smart enough to drop theruby
), so comparing the two tells you precisely that: is this the file that was executed from the command line? This is sometimes done by coders who want to define a class/module in a file and also provide a command-line utility that uses it. IMHO that's not very good project structure, but just like anything there are use cases where doing it makes perfect sense.If you want to be able to execute your code directly, you can add a shebang line
and make it executable with
chmod +x somefile.rb
(optionally rename it without the .rb extension). This doesn't really change your situation. Theif __FILE__ == $0
still works and still probably isn't necessary.Edit
As @steenslag correctly points out, the top-level scope in Ruby is an
Object
calledmain
. It has slightly funky behavior, though:Don't worry about this until you start to dig much deeper into the language. If you do want to learn lots more about this kind of stuff, Metaprogramming Ruby is a great read :)
Actually there is a
main
, but it is not a method; it's the top-level object that is the initial execution context of a Ruby program.No there isn't such structure. Of course you can define main function but it won't be called until you do so. Ruby execute line by line so if you want to print 'Hello World' you simply write:
The question that you mentioned is about using one file as module and executable, so if you write
It will be called only if you run this file. If you only require it in other file then this code will never run. But IMHO it's bad idea, better option is using RubyGems and there add executables.