Re: Exclamation points in quoted strings

[Chet Ramey]

Ethan Glasser-Camp wrote:
> Hi,
> 
> I'm not a shell script pro and I don't know much about POSIX, but I
> have found this puzzling behavior in bash, and although it is
> documented I don't really understand why bash behaves this way. I was
> hoping someone could tell me.
> 
> ethan@sundance:~$ set -H
> ethan@sundance:~$ echo "hi!"
> bash: !": event not found

Only single quotes or an unquoted backslash can inhibit history
expansion.  This is inherited from the features's csh heritage.

> ethan@sundance:~$ echo "hi\!"
> hi\!
> 
> This is somewhat unusual; generally, characters protected by
> backslashes are put through *unescaped*. Compare:
> 
> ethan@sundance:~$ echo "\`"
> `
> ethan@sundance:~$ echo "\""
> "
> ethan@sundance:~$ echo "hi\$"
> hi$

Not true, in general.  Posix specifies the characters the backslash
can escape in double-quoted strings.  You happened to choose three of
the five.

http://www.opengroup.org/onlinepubs/009695399/utilities/xcu_chap02.html#tag_02
_02_01

  The backslash shall retain its special meaning as an escape character
  (see Escape Character (Backslash)) only when followed by one of the
  following characters when considered special:

      $   `   "   \   <newline>


Chet
-- 
``The lyf so short, the craft so long to lerne.'' - Chaucer
                       Live Strong.  No day but today.
Chet Ramey, ITS, CWRU    chet@case.edu    http://cnswww.cns.cwru.edu/~chet/