Source shell script into environment within a ruby script

Question

If I'm writing a shell script and I want to "source" some external (c-)shell scripts to set up my environment, I can just make calls like this:

source /file/I/want/to/source.csh

I want to replace a shell script that does this with a ruby script. Can I do a similar thing in the ruby script?

Update:

Just tried it with test_script.csh:

#!/bin/csh

setenv HAPPYTIMES True

...and test_script.rb:

#!/usr/bin/env ruby
system "~/test_script.csh"
system "echo $HAPPYTIMES"

Sadly, no HAPPYTIMES as of yet.

Answer 1

Given the following Ruby

# Read in the bash environment, after an optional command.
#   Returns Array of key/value pairs.
def bash_env(cmd=nil)
  env = `#{cmd + ';' if cmd} printenv`
  env.split(/\n/).map {|l| l.split(/=/)}
end

# Source a given file, and compare environment before and after.
#   Returns Hash of any keys that have changed.
def bash_source(file)
  Hash[ bash_env(". #{File.realpath file}") - bash_env() ]
end

# Find variables changed as a result of sourcing the given file, 
#   and update in ENV.
def source_env_from(file)
  bash_source(file).each {|k,v| ENV[k] = v }
end

and the following test.sh:

#!/usr/bin/env bash
export FOO='bar'

you should get:

irb(main):019:0> source_env_from('test.sh')
=> {"FOO"=>"bar"}
irb(main):020:0> ENV['FOO']
=> "bar"

Enjoy!

Answer 2

The reason this isn't working for you is b/c ruby runs its system commands in separate shells. So when one system command finishes, the shell that had sourced your file closes, and any environment variables set in that shell are forgotten.

If you don't know the name of the sourced file until runtime, then Roboprog's answer is a good approach. However, if you know the name of the sourced file ahead of time, you can do a quick hack with the hashbang line.

% echo sourcer.rb
#!/usr/bin/env ruby
exec "csh -c 'source #{ARGV[0]} && /usr/bin/env ruby #{ARGV[1]}'"
% echo my-script.rb
#!/usr/bin/env ruby sourcer.rb /path/to/file/I/want/to/source.csh
puts "HAPPYTIMES = #{ENV['HAPPYTIMES']}"
% ./my-script.rb
HAPPYTIMES = True

All of these will only help you use the set enviroment variables in your ruby script, not set them in your shell (since they're forgotten as soon as the ruby process completes). For that, you're stuck with the source command.

Answer 3

Improving a little on @takeccho's answer... Checks, and a few whistles. First, the sourced environment is cleaned via env -i, which is a safety measure but might be not desired in some cases. Second, via set -a, all variables set in the file are "exported" from the shell and thus imported into ruby. This is useful for simulating/overriding behavior found in environment files used with init scripts and systemd env files.

def ShSource(filename)
  # Inspired by user takeccho at http://stackoverflow.com/a/26381374/3849157
  # Sources sh-script or env file and imports resulting environment
  fail(ArgumentError,"File #{filename} invalid or doesn't exist.") \
     unless File.exist?(filename)

  _newhashstr=`env -i sh -c 'set -a;source #{filename} && ruby -e "p ENV"'`
  fail(ArgumentError,"Failure to parse or process #{filename} environment")\
     unless _newhashstr.match(/^\{("[^"]+"=>".*?",\s*)*("[^"]+"=>".*?")\}$/)

  _newhash=eval(_newhashstr)
   %w[ SHLVL PWD _ ].each{|k|_newhash.delete(k) }
  _newhash.each{|k,v| ENV[k]=v } # ENV does not have #merge!
end

Theory of operation: When ruby outputs the ENV object using p, it does so in a way that ruby can read it back in as an object. So we use the shell to source the target file, and ruby (in a sub-shell) to output the environment in that serializable form. We then capture ruby's output and eval it within our ruby-process. Clearly this is not without some risk, so to mitigate the risk, we (1) validate the filename that is passed in, and (2) validate using a regexp that the thing we get back from the ruby-subshell is, in fact, a serializable hash-string. Once we're sure of that, we do the eval which creates a new hash. We then "manually" merge the hash with ENV, which is an Object and not a regular Hash. If it were a Hash, we could have used the #merge! method.

EDIT: sh -a exported things like PATH. We must also remove SHLVL and PWD before the hash-merge.