shell.md

Calling out to the Shell

There are a number of ways to invoke shell tasks from within Rake (and Ruby).

• exec my_command
• success = system my_command (success is a boolean)
• stdout = `my_command` (the backtick, stdout is a string)
• stdout = %x{my_command} (stdout is a string)
• result = sh %{my_command} {} (result is an object, result.success? is a useful method to remember)
• result = sh "my_command" {} (as above)
• O#popen(cmd) { |io| } (Run a subprocess and connect stdout and stderr to io)
• stdin, stdout, stderr = Open3.popen3(cmd) (Run a subprocess and connect to all pipes: in, out, err)

%x{} returns back to rake task whereas exec and system does not (exec replace the current process with a new one, system return true or false)

The rake preferred way is to use the sh method because:

1. it aborts if the return is != 0
2. the command itself is echoed before the output

Exercise

Write a simple shell-based concatenation task that will merge all the markdown files into a single long one in the data directory called rake_book.md. Hint: use cat *.md to get the shell to do the merge and a shell pipe > to redirect the output to a file.