Re: sed with Variable Substitution in the command

[Andreas Kähäri]

On Thu, Sep 26, 2024 at 02:21:06PM -0400, Greg Wooledge wrote:
> On Thu, Sep 26, 2024 at 20:03:10 +0200, Andreas Kähäri wrote:
> > On Thu, Sep 26, 2024 at 01:16:21PM -0400, Greg Wooledge wrote:
> 
> > > > On Thursday, September 26, 2024, Wiley Young <wyeth2485@gmail.com> 
> > > > wrote:
> > > > > "${1}"
> > > > >             "$1" is okay
> > > > > "${11}"
> > > > >             "$11" is an error
> 
> > > $11 would be equivalent to ${1}1 which is not what's intended.
> > 
> > How do you know it's not intended? ;-) "Intention" is not something that
> > can be inferred from the syntax of small fragment of a shell script.
> 
> In this case, what we were given by Wiley Young is not a shell script.
> It's a document.  The document shows shell syntax in one column, and
> gives an explanation or comment in the second column.
> 
> The document is telling us that there is a difference between "${11}"
> and "$11".  One is right, and the other is an error.
> 
> The context of Wiley's post was "when are braces required, and when are
> they optional".  ${1} is a case where the braces are optional, while
> ${11} is a case where they are required.
> 
> There is no ambiguity here.  The intent is completely clear.

There was never an intention stated in the text, as far as I can see.

I'm saying that "$11" is not an error, if what you want is to is the
value of the first positional parameter cancatenated by the string "1"
(which is a completely valid thing to want).  If that is the intention,
then "$11" is correct, and "${11}" is an error.

If your intention is to get the value of the 11th positional parameter,
then you should use "${11}".  However, it was never stated what the
intention was, only that "${11}" was "correct" and "$11" was an "error"
("unintended effects will occur").

You simply can't say that "$11" is an error without knowing what the
rest of the code is supposed to do.

-- 
Andreas (Kusalananda) Kähäri
Uppsala, Sweden

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