til/ruby/execute-several-commands-with-backtick-heredoc.md

Execute Several Commands With Backtick Heredoc

A fun feature of Ruby is that we can execute a command in a subprocess just by wrapping it in backticks.

For instance, we might shell out to git to check if a file is tracked:

`git ls-files --error-unmatch #{file_path} 2>/dev/null`
$?.success?

But what if we need to execute several commands? Perhaps they depend on one another. We want them to run in the same subprocess.

For this, we can use the backtick version of a heredoc. That is a special version of a heredoc where the delimiter is wrapped in backticks.

puts <<`SHELL`
  # Set up trap
  trap 'echo "Cleaning up temp files"; rm -f *.tmp' EXIT
  
  # Create temporary file
  echo "test data" > work.tmp
  
  # Do some work
  cat work.tmp
  
  # Trap will clean up on exit
SHELL

Here we set up a trap for file cleanup on exit, then create a file, then do something with the file, and that's it, the process exits (triggering the trap).

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