# Carats are irreplaceable? (String#tr quandry)

**URL:** <https://www.ruby-forum.com/t/carats-are-irreplaceable-string-tr-quandry/64323>\
**Category:** Ruby\
**Created:** [June 24, 2006, 6:35am UTC](https://www.ruby-forum.com/t/carats-are-irreplaceable-string-tr-quandry/64323 "2006-06-24T06:35:22Z")\
**Posts on this page:** 3\
**Page:** 1

<div class="post-metadata">

**Author:** ![makenai](https://www.ruby-forum.com/letter_avatar_proxy/v4/letter/m/8797f3/32.png) [@makenai](https://www.ruby-forum.com/u/makenai)\
**Post date:** [June 24, 2006, 6:35am UTC](https://www.ruby-forum.com/t/carats-are-irreplaceable-string-tr-quandry/64323/1 "2006-06-24T06:35:22Z")

</div>

Hi all,

I ran into a little problem with String#tr today. I wanted to do  
something like:

str = ‘kame^hame^ha^’  
str.tr(’^’,’-’)

But I got back an error about having a nil character class ([^]).  
According to the docs: “Both strings may use the c1?c2 notation to  
denote ranges of characters, and from\_str may start with a ^, which  
denotes all characters except those listed.”

So it’s trying to interpret the first argument as some sort of a  
single character regex, even though it’s in a string. Bummer. How then  
can I replace a carat character in my string?

str.tr(’^’,’-’) doesn’t seem to work either.

Is there any way of doing this? I know that I can just use gsub  
instead and go on with my life (I have actually), but this is  
bothering me for some reason.

Thanks!

-Pawel

---

<div class="post-metadata">

**Author:** ![makenai](https://www.ruby-forum.com/letter_avatar_proxy/v4/letter/m/8797f3/32.png) [@makenai](https://www.ruby-forum.com/u/makenai)\
**Post date:** [June 24, 2006, 6:44am UTC](https://www.ruby-forum.com/t/carats-are-irreplaceable-string-tr-quandry/64323/2 "2006-06-24T06:44:35Z")

</div>

irb(main):003:0\> str = ‘kame^hame^ha^’  
=\> “kame^hame^ha^”  
irb(main):004:0\> str.tr ‘^’, ‘-’  
=\> “kame-hame-ha-”

---

<div class="post-metadata">

**Author:** ![makenai](https://www.ruby-forum.com/letter_avatar_proxy/v4/letter/m/8797f3/32.png) [@makenai](https://www.ruby-forum.com/u/makenai)\
**Post date:** [June 24, 2006, 7:03am UTC](https://www.ruby-forum.com/t/carats-are-irreplaceable-string-tr-quandry/64323/3 "2006-06-24T07:03:08Z")

</div>

On 6/23/06, Mark Van H. [removed\_email\_address@domain.invalid](mailto:removed_email_address@domain.invalid) wrote:

> irb(main):003:0\> str = ‘kame^hame^ha^’  
> =\> “kame^hame^ha^”  
> irb(main):004:0\> str.tr ‘^’, ‘-’  
> =\> “kame-hame-ha-”

Oops - thanks for the reality check, Mark.

I just realized that the exception occurs in jcode, not in the core:

irb(main):001:0\> str = ‘kame^hame^ha^’  
=\> “kame^hame^ha^”  
irb(main):002:0\> str.tr ‘^’,‘-’  
=\> “kame-hame-ha-”  
irb(main):003:0\> require ‘jcode’  
=\> true  
irb(main):004:0\> str.tr ‘^’,‘-’  
RegexpError: invalid regular expression; empty character class: /[^]/  
from /usr/local/lib/ruby/1.8/jcode.rb:137:in `tr!' from /usr/local/lib/ruby/1.8/jcode.rb:148:in `tr’  
from (irb):4  
irb(main):005:0\>

That’s weird I guess, but not as surprising as if was in the core  
String behavior. I can live with this. Sorry for the false alarm -  
it’s been a long night!

-Pawel