[Ruby] Confirm existance of executable (script, bat, cmd, exe) via a ruby file.

Question

Using a ruby file (or any rake facility) I need to find out if the user who executes my script is able to execute certain shell commands. In particular g++ etc. Hopefully system independent so if there is some g++.bat, g++.exe or just g++ (etc) it should say yes nevertheless, as long as its on the path and executable on the users system.

Example: if the user has a no-extention executable version of the file and a .cmd version of the file it should say "yes" for the no extension version on a linux system and "yes" to the .cmd version on a windows system. Since the users shell can only execute that version of the file.

The purpose of this is to allow the script to be self-configuring (as much as possible).

Any suggestions on how I might go about doing this?

Answer 1

Well, File contains both exists? and executable?. ENV['PATH'] gets the directories executables are in (at least on *nix - can someone confirm for Windows?). Combine the two with a bit of magic and you should have a solution.

Edit:

irb(main):001:0> ENV['PATH'].split(':').collect {|d| Dir.entries d if Dir.exists? d}.flatten.include? 'adduser'
=> true
irb(main):002:0> ENV['PATH'].split(':').collect {|d| Dir.entries d if Dir.exists? d}.flatten.include? 'foo'
=> false

Answer 2

A quick and dirty way is to simply attempt to execute g++ via the system command and check the return code, for example:

def gpp_exists
  return system("g++ --version")
end

You'd have to do some trickery to avoid getting unwanted output on the console (e.g. redirecting stdout/stderr based on correct OS syntax), but it couldn't be too bad.