Add Get The Output Of Running A System Program as a Ruby TIL

ruby/get-the-output-of-running-a-system-program.md

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+# Get The Output Of Running A System Program
+
+Ruby has a [variety of ways](https://stackoverflow.com/a/18623297/535590) to
+execute a system program within a Ruby process. The backticks approach is the
+handy shorthand approach to reach for if you want to capture the output of the
+command.
+
+For instance, let's say I want to capture the connection string credentials
+output by running a `heroku` command. When the command is wrapped in backticks,
+Ruby will execute it in a subprocess and the output of the command will be the
+return value.
+
+```ruby
+result = `heroku pg:credentials:url DATABASE_URL --app my-app`
+
+# extract connection details
+connection_info = result.split("\n")[2].strip
+```
+
+With the result in hand, I can use Ruby to parse out the details I'm interested
+in.
+
+Backticks does two other nice things. It allows for string interpolation and it
+puts the process status (e.g. exit code) on
+[`$?`](check-return-status-of-running-a-shell-command.md).