Re: Escaping the history expansion character

[Chet Ramey]

Matthew Walker wrote:

>  From the bash info page:
>   Only `\' and `'' may be used to escape the history expansion
>   character.
>
> I have tried the following:
>   echo '!'   # works fine, displays "!"
>   echo "!"   # errors as expected with "event not found"
>   echo "\!"  # produces "\!" --- this is my problem
>
> Why is it that "\!" doesn't output just "!"?
>
> For every other scenario "\x" produces "x".  Why does this fail for an 
> exclamation mark?

Because `!' is not one of the characters for which the backslash retains
its meaning as an escape character when in double quotes.

See

http://www.opengroup.org/onlinepubs/009695399/utilities/xcu_chap02.html#tag_02_02_03

for that list of characters.

This is one of the places where the csh-derived history expansion
collides with bash's sh-based syntax.

Chet