Checking external dependencies during the installation

ruby-talk
1

Dear list member,

I'm packaging some scripts as gems on my Linux based box, and I need to
check during the runtime after the first script invocation if all
external dependences (like e.g. `ls`) are installed and present on the
machine.

A couple of weeks ago I found a mention about a working library, but
totally forgot the library name and cannot find it again.

Any ideas what it the best tool for checking for external dependencies?

Thanks in advance,

arbox

2

Hi,

(like e.g. `ls`)

For this particular task you should probably better be using Ruby's
internal Dir.glob/Dir.foreach methods or the Find module from the
stdlib.

check during the runtime after the first script invocation if all
external dependences

I don’t know of a library that does this, but you can certainly code
something up as it's not too complicated. A very easy approach would be
to use the #system method and check if invocation of the program in
question is possible by checking its return value. A more complete
approach would search ENV["PATH"] (and additionally try an invocation).

A quick’n’dirty solution that searches PATH and tries to invocate the
program with the "--help" switch to see it is present and works:

def find_program(progname)
  ENV["PATH"].each do |dir|
    Dir.foreach(dir) do |filename|
      if filename == progname
        full_path = "#{dir}/#{filename}"
        if system("#{full_path} --help")
          return full_path
        end
      end
    end
  end

  false
end

This is untested. It can certainly be improved, but you get the general
idea.

Greetings
Marvin

···

Am Thu, 26 May 2016 22:35:56 +0200 schrieb Andrei Beliankou <arbox@yandex.ru>:

--
Blog: http://www.guelkerdev.de
PGP/GPG ID: F1D8799FBCC8BC4F

3

Thank you, Marvin,

I don’t know of a library that does this, but you can certainly code

yes, I'm aware of `system` based approaches and use it now.

Google is damn unreliable... I found this library a couple of weeks ago,
and now I cannot...

Best,
arbox