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

README.md

@@ -10,7 +10,7 @@ pairing with smart people at Hashrocket.
 
 For a steady stream of TILs, [sign up for my newsletter](https://crafty-builder-6996.ck.page/e169c61186).
 
-_1218 TILs and counting..._
+_1219 TILs and counting..._
 
 ---
 
@@ -984,6 +984,7 @@ _1218 TILs and counting..._
 - [Generate A Signed JWT Token](ruby/generate-a-signed-jwt-token.md)
 - [Generate Ruby Version And Gemset Files With RVM](ruby/generate-ruby-version-and-gemset-files-with-rvm.md)
 - [Get Info About Your RubyGems Environment](ruby/get-info-about-your-ruby-gems-environment.md)
+- [Get The Output Of Running A System Program](ruby/get-the-output-of-running-a-system-program.md)
 - [Identify Outdated Gems](ruby/identify-outdated-gems.md)
 - [If You Detect None](ruby/if-you-detect-none.md)
 - [Iterate With An Offset Index](ruby/iterate-with-an-offset-index.md)

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

@@ -0,0 +1,25 @@
+# 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).