Find declared function from user input

Question

I have a prompt in my "app", like irb that takes an input,I want it to parse the input and execute a function that I've defined. Similarly, my app takes an input through gets, and calls the function. For example,

command = gets.gsub("\n","")

takes an input "pwd", now I want to call the function pwd, which is defined below:

def pwd
  Dir.pwd
end

Now, I could simply use if conditions to do so, but a lot of these conditions wouldn't be as elegant as Ruby's philosophy requires it to be.

The Question

I want to parse the input to call a defined function. Like, "pwd" calls pwd, "ls" calls its equivalent function that I have defined.

How do I do this? Comment if question is still not clear. Cheers.

Addressing Possible Duplicate

The question suggested specifically wants to run Shell commands. Whereas, I am using only built-in Ruby methods and classes and maybe in the future I'll even use Gems, so as to attain platform independence. My commands may look and behave like shell, but I'm not actually running shell. Therefore, my question is not a possible duplicate.

Furthermore, future readers will find it helpful for parsing input in Ruby.

It isn't. That's the point. I made my own function and I'll call it using "ls" — Faraaz Ahmad, Feb 10 '17 at 15:59
So if the command is "pwd", then Ruby should call `Dir.pwd` and if the command is "ls", then Ruby should call your own `ls` method. Is that correct? — Stefan, Feb 10 '17 at 16:03
Oh, you've edited your question. Is there a class that has a method with the same name for each command? — Stefan, Feb 10 '17 at 16:08
No. I just have `pwd.rb`, `ls.rb` etc, and I `require` them. Will it help if there are classes for these functions? — Faraaz Ahmad, Feb 10 '17 at 16:14
Possible duplicate of [Calling shell commands from Ruby](http://stackoverflow.com/questions/2232/calling-shell-commands-from-ruby) — Bustikiller, Feb 10 '17 at 17:16

score 1 · Accepted Answer · answered Feb 10 '17 at 15:54

1

You can write a mapping for the different inputs in the form of a case:

case command
when "pwd"
  Dir.pwd # or move it into another method and call it here
when "ls"
  # etc
end

or a hash, which is slightly more concise

actions = {
  pwd: -> { Dir.pwd },
  ls: -> { <foobar> } 
}
actions[command.to_sym].call

You can also make method names matching the commands and use send, but don't do this if the input is coming from strangers:

def pwd
  Dir.pwd
end

command = command.to_sym
send(command)

answered Feb 10 '17 at 15:54

max pleaner

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I'm already on the third approach. However, command is a string. `to_sym` will only make, for example `:"pwd"` – Faraaz Ahmad Feb 10 '17 at 15:58
Yes, what is wrong with that? You pass a symbol to `send`, `:"pwd"` is a symbol. – max pleaner Feb 10 '17 at 17:28
But that wont call `pwd`, will it? – Faraaz Ahmad Feb 10 '17 at 17:39
1

yes, `send(:pwd)` will call the `pwd` method you've defined. – max pleaner Feb 10 '17 at 17:43

Find declared function from user input

1 Answers1