Re: bash: exclamation mark is not literal within double quotes

[Richard Neill]

Chet Ramey wrote:
> > Machine Type: i586-mandrake-linux-gnu
> >
> > Bash Version: 2.05b
> > Patch Level: 0
> > Release Status: release
> >
> > Description:
> >         Error in the documentation. The manual says:
>
>
> The current version of bash is 3.0.  The bash-3.0 manual page says:
>
> When command history is being used, the double quote may not be used to
> quote the history expansion character.
>
> Chet

Indeed it does. However, it's somewhat confusing, because the manual 
includes both:

(1)     "When  the command history expansion facilities are being used,
        the history expansion character, usually !, must be quoted to
        prevent  history expansion."

and

(2)     Enclosing characters in double quotes preserves the  literal    
	value  of all characters  within  the quotes, with the exception 	of $, 
`, and \.
	The characters $ and `  retain  their  special  meaning  within 
double	quotes. The  backslash retains its special meaning only 	
        when followed by one of the following characters: $, `, ", \, or
        <newline>.  A double quote  may  be quoted within double quotes
        by preceding it with a backslash.  When command history is being
        used, the double quote may not be used to quote the history
        expansion character."


The first tells me that I *must* quote it; the second tells me that I 
cannot do so!


May I suggest the following changes:

1)It is a bug that ! cannot be quoted within double quotes, not even by 
backslash. For example, the following ought to work:
        
        WARNING="Bad $USER\! Go $HOME\!"  ; echo $WARNING


2)Shouldn't history expansion be off in a shell script anyway?


3)Personally, I still find the  paragraph (2) unclear. It seems to me 
that someone making a quick reference to quoting won't understand it. 
May I suggest this instead:

        Enclosing characters in double quotes preserves the  literal    
	value  of all characters  within  the quotes, with the exception 	of $, 
`, and \. The history expansion character, usually ! is 	
        also special.

        The characters $, ` and ! retain  their  special  meaning
        within  double  quotes. The  backslash retains its special
        meaning only when followed by one of the following characters:
        $, `, ", \, !,     or <newline>.  \$, \`, \", \! and \\ result in
        literal $,`,",!,\ respectively. \<newline> is ignored.

        " and ` will nest as expected without requiring addition
        escapes: eg echo "Today is `date "+%Y %m %d"`."
        

Please do change the behaviour to allow \!    Otherwise, one has to 
write really contrived scripts such as:
        
        echo "Hello $USER"'!'" How are you?"


Regards

Richard