Gsub and slash-ampersand in the substitution string

ruby-talk
1

Greetings,

I'm trying to do something that should be very simple: stick a "\" in
front of
every instance of "&" in a string. However, the obvious code...

  "this&that".gsub!("&", "*")
  --> "this*that" # OK!

  "this&that".gsub!("&", "\\&")
  --> "this&that" # Wrong

...doesn't work, because "\&" means "last match" in gsub substitution
strings.
How can I escape this? I experimentally determined that entering
"\\\\\\&"
(that's six backslashes) gets the desired result, but I don't really
understand why. Is there a less obscure way of doing this?

Cheers,
-jani

···

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Posted via http://www.ruby-forum.com/.

2

I'm not sure, but I think that the problem is that you are using double
quotes. So, the value you are passing is really the same as:

    '\\\&'

Which, once you interpret the escape sequences, you have a literal '\' and a
literal '&'...

···

On Mon, Oct 09, 2006 at 08:58:09PM +0900, Jani Patokallio wrote:

Greetings,

I'm trying to do something that should be very simple: stick a "\" in
front of
every instance of "&" in a string. However, the obvious code...

  "this&that".gsub!("&", "*")
  --> "this*that" # OK!

  "this&that".gsub!("&", "\\&")
  --> "this&that" # Wrong

...doesn't work, because "\&" means "last match" in gsub substitution
strings.
How can I escape this? I experimentally determined that entering
"\\\\\\&"
(that's six backslashes) gets the desired result, but I don't really
understand why. Is there a less obscure way of doing this?

--
Esteban Manchado Velázquez <zoso@foton.es> - http://www.foton.es
EuropeSwPatentFree - http://EuropeSwPatentFree.hispalinux.es

3

this was discussed several times, try searching for gsub and \\ or
escaping or something similar. \& is the last match, and \\ is the
whole match. so you need to escape both. The correct solutions to this
'quiz' are posted somewhere, just google it :wink:

···

On 10/9/06, Esteban Manchado Velázquez <zoso@foton.es> wrote:

On Mon, Oct 09, 2006 at 08:58:09PM +0900, Jani Patokallio wrote:
> Greetings,
>
> I'm trying to do something that should be very simple: stick a "\" in
> front of
> every instance of "&" in a string. However, the obvious code...
>
> "this&that".gsub!("&", "*")
> --> "this*that" # OK!
>
> "this&that".gsub!("&", "\\&")
> --> "this&that" # Wrong
>
> ...doesn't work, because "\&" means "last match" in gsub substitution
> strings.
> How can I escape this? I experimentally determined that entering
> "\\\\\\&"
> (that's six backslashes) gets the desired result, but I don't really
> understand why. Is there a less obscure way of doing this?

    I'm not sure, but I think that the problem is that you are using double
quotes. So, the value you are passing is really the same as:

    '\\\&'

Which, once you interpret the escape sequences, you have a literal '\' and a
literal '&'...

--
Esteban Manchado Velázquez <zoso@foton.es> - http://www.foton.es
EuropeSwPatentFree - http://EuropeSwPatentFree.hispalinux.es