Re: Context sensitivity of the word "parameter" in the section of "Parameter Expansion"

[Eli Schwartz]

On 5/9/21 11:59 AM, Peng Yu wrote:
> Hi,
> 
> In the following paragraph in the manual, "parameter" in
> "${parameter}" could be "!".
> 
> """
>        ${parameter}
>               The value of parameter is substituted.  ...
> """
> 
> However, "parameter" in "${#parameter}" can not be "!".
> 
> """
>        ${#parameter}
>               Parameter length. ...
> """
> 
> $ echo "${!}"
> 57766
> $ echo "${#!}"
> -bash: !}: event not found

Works for me.

$ echo $!

$ echo ${#!}
0


Try disabling history expansion, it tends to confuse things quite a bit
before anything else. You need single quotes to suppress it, which means
you cannot *also* do variable expansion, though you could fudge it with
single-quoted assignment and `eval`.


> So the word "parameter" in "${parameter}" and "${#parameter}" is not
> the exactly same. Should this be made clearer in the manual?
> 
> I have not checked "parameter" in all the cases in this section. But I
> guess the word "parameter" in the whole section should be check for
> ambiguity like this?
> 
> This sentence is also not precise. ${!} obviously satisfies that the
> first character is "!" and it is not a nameref. Yet ${!} is just the
> process ID instead of a level of indirection.
> 
> "       If the first character of parameter is an exclamation  point  (!),  
> and
>        parameter is not a nameref, it introduces a level of indirection."
> 


-- 
Eli Schwartz
Bug Wrangler and Trusted User

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