Re: [patch] new special variable: test argument

[Stephane Chazelas]

2015-12-19 00:58:41 +0100, Piotr Grzybowski:
>  Thanks for taking time to answer. Of course it is the issue of
> programming style (isnt it true that most things can be brought down
> to the programming style?), two real-life examples (stripped-down of
> everything):
> 
> #1
> if [ -f ${output}/${branch}/${index}/${current} ]; then
>  let current--;
>  for((i=0;i<${branch};i++)) do
>   index=`new_index ${current} ${index}`;
>  done;
>  echo "$^ already filled, regenerating index ${index}/${current}";
>  find ${backup}/`basename $^` -type f -exec cp `dirname "$^"/* [..]`
>  rebuilt ${output} -previous "$^" -branch ${branch} ${index}/${current};
> fi;
> 
> lets assume that for some wicked reason you do not need another local
> variable l=${output}/${branch}/${index}/${current}, besides you would
> need to remember that it consists of many parts, assemble and
> reassemble it, remembering some previous values, also for some reasons
> you cant refactor the above code (which of course always can remove
> the need for any special variables): lets say that it reflects some
> logic. Without $^ it begins to look terrible.

Using a variable is the most obvious thing to do.

Also, what if "new_index" was a function which does call "[ -f"
on another file?

You've got a lot variables and command substitutions that need
quoted here btw.


> #2
> touch /tmp/`date +%s`; if [ -f /tmp/`date +%s` ]; then echo "ok: $^"; fi;
> 
> just a quick example (the real one was much more complicated in terms
> of `` and the latter use of $^) of auto-generated code whos author
> really did not want to use another variable, as it would be a waste of
> space in his generating code. Without $^ the above requires more care.
>  As for the all-purpose perl-alike $_ of course I have some ideas,
> just let me think, and lets just hope I will not retreat into myself
> after you say that $^ is useless ;-)
[...]

Again, use a variable. Not using a variable is even wrong here,
as those two calls of "date" could return a different result.

-- 
Stephane