Write a simple error message without a backtrace

I want to write to either STDOUT or STDERR a clean, simple error message for the user, without the (verbose) backtrace. I am currently using raise to write the error message and exit, as in this simplified example:

#!/usr/bin/env ruby

def bar
  raise "this needs to be clean, no backtrace"
end

bar

It writes this to STDERR:

/Users/foo/test/test1.rb:4:in `bar': this needs to be clean, no backtrace (RuntimeError)
        from /Users/foo/test/test1.rb:7:in `<main>'

I want to write just this part:

this needs to be clean, no backtrace 

The real-life example has a much more verbose backtrace, and multiple raise statements to handle different failure modes with customized messages.

I am aware that I can do something like this (for clean STDOUT), but I want to avoid repetitive code:

puts "this needs to be clean, no backtrace"
raise "this needs to be clean, no backtrace"

Related:

• Unhandled Exceptions in Ruby - this answer suggests a more complex way of handling exceptions (namely, catching and printing the error message) than I need. All I need is: (a) raise - or something similar - to terminate the program immediately, and (b) print just the error message, not the full stack trace or backtrace, which is confusing for our users.

If you just want to output to stderr, you could use warn (or write to $stderr directly), maybe along with exit:

def bar
  warn "this needs to be clean, no backtrace"
  exit(false)
end

bar

To alter the way global exception handlers work, you could register an at_exit handler which checks for the exception class, prints its message and silences stdout in order to suppress the backtrace. Something like this:

class SimpleError < StandardError ; end

at_exit do
  if $!.is_a?(SimpleError)
    $stderr.puts($!.message)
    $stderr.reopen(IO::NULL)
  end
end

def bar
  raise SimpleError, "this needs to be clean, no backtrace"
end

bar

It would probably be a good idea to make that kind of error handling optional.