Add Check Return Status Of Running A Shell Command as a ruby til

ruby/check-return-status-of-running-a-shell-command.md

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+# Check Return Status Of Running A Shell Command
+
+There are [many
+ways](http://tech.natemurray.com/2007/03/ruby-shell-commands.html) to run a
+shell command in a Ruby context. One of the most common is to place the command
+inside backticks. It runs the command in a subshell.
+
+The standard output (`stdout`) from running the command is the return value of
+the statement. Ruby also captures details about the previously run command in
+the global `$?` variable.
+
+
+```ruby
+> `true`
+=> ""
+> $?.exitstatus
+=> 0
+
+> `false`
+=> ""
+> $?.exitstatus
+=> 1
+
+> `echo 'hello' && exit 2`
+=> "hello\n"
+> $?
+=> #<Process::Status: pid 12284 exit 2>
+> $?.exitstatus
+=> 2
+```
+
+The value captured in `$?` is a `Process::Status` object. It can tell us the
+exit status of the process with `#exitstatus`.