Exporting an Environment Variable in Ruby

Question

How do I export an environment variable from within a Ruby script to the parent shell? For example, implementing a naïve implementation of the read Bash builtin:

#!/usr/bin/ruby  varname = ARGV[0] ENV[varname] = STDIN.gets  # but have varname exported to the parent process 

Answer 1

You can't export environment variables to the shell the ruby script runs in, but you could write a ruby script that creates a source-able bash file.

For example

% echo set_var.rb #!/usr/bin/env ruby varname = ARGV[0] puts "#{varname}=#{STDIN.gets.chomp}" % set_var.rb FOO 1 FOO=1 % set_var.rb BAR > temp.sh ; . temp.sh 2 % echo $BAR 2 % 

Another alternative is that using ENV[]= does set environment variables for subshells opened from within the ruby process. For example:

outer-bash% echo pass_var.rb #!/usr/bin/env ruby varname = ARGV[0] ENV[varname] = STDIN.gets.chomp exec '/usr/bin/env bash' outer-bash% pass_var.rb BAZ quux inner-bash% echo $BAZ quux  

This can be quite potent if you combine it with the shell's exec command, which will replace the outer-shell with the ruby process (so that when you exit the inner shell, the outer shell auto-exits as well, preventing any "I thought I set that variable in this shell" confusion).

# open terminal % exec pass_var.rb BAZ 3 % echo $BAZ 3 % exit # terminal closes