Mark Needham

Thoughts on Software Development

Ruby: invalid multibyte char (US-ASCII)

with one comment

I’ve used Ruby on and off for the last few years but somehow had never come across the following error which we got last week while attempting to print out a currency value:


amount = "£10.00"
puts amount
$ ruby blah.ruby 
blah.ruby:1: invalid multibyte char (US-ASCII)
blah.ruby:1: invalid multibyte char (US-ASCII)

Luckily my pair Jae had come across this before and showed me a blog post which explains what’s going on and how to sort it out.

It turns out that since Ruby 1.9 we need to explicitly specify which encoding we want to use for strings otherwise it will default to US-ASCII in my case at least.

We can get around this by explicitly telling the interpreter that we want to use UTF-8 encoding by including the following comment at the top of our file:

# encoding: UTF-8
amount = "£10.00"
puts amount

Then when we interpret the file this time:

$ ruby blah.ruby 

Since we were only editing one file it made sense to just set the comment manually but if we need to do that in a more widespread way then we’d want to use the magic_encoding gem.

Yehuda Katz also wrote a post a few years ago explaining all things encoding in more detail.

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Written by Mark Needham

January 27th, 2013 at 3:14 pm

Posted in Ruby

Tagged with

  • thanks for this – I couldn’t work out why my sprintf syntax was failing…