Re: optimal expansions?

["Lawrence Velázquez" <larryv@zsh.org>]

On Fri, Apr 19, 2024, at 3:22 PM, Ray Andrews wrote:
> That's my preferred way to look at 'apt-file search' output (Debian and 
> derivatives only of course).  It works fine and I think I understand 
> all the expansions and splitting.  One you get used to it the nested 
> expansions aren't so scary, just read them from inside out, one step at 
> a time and it's easy.  But is it optimal?

How is anyone supposed to answer this question, when you haven't
deigned to mention what your code is supposed to DO?  You seem to
colorize certain portions of the output by bracketing them with
escape sequences, but which portions, exactly?  What does
"apt-file search" typically output?

Without knowing more about the bigger picture, the best we can do
is nitpick your code without addressing its larger structural issues.
(Unless someone wants to guess about your intentions.)


> Script:
>
>     grn=$'\e[32;1m'
>     nrm=$'\e[0m'
>
>     var=( "${(@f)$(apt-file search $1)}" )

You don't check the exit status of "apt-file", so if it happens to
fail for any reason, your code plows on obliviously, printing nothing
and exiting with a zero status.  You should do something like

	var=( "${(@f)$(apt-file search -- $1)}" ) || return

(assuming this is all in a function, since you have yet again chosen
to not provide any context)


>     targ=
>     var2=()
>        
>     for ((i=1; i<=$#var; i++ )); do

Since you only ever use "i" in the expansion "${=var[i]}", there
is no reason to use this form of "for".  You can just use the usual

	for x in "$var[@]"; do

and subsequently "$x" instead of "$var[i]".


>         if [[ "$targ" != "${${=var[i]}[1]}" ]]; then
>             targ="${${=var[i]}[1]}"
>             var2+="\n${grn}${${=var[i]}[1]}${nrm}" # Copy first word of 
> line.

You're doing that thing again, where you use a literal backslash-n
and rely on "print" to interpret it as a newline.  This is bad
practice here because the rest of the string is the arbitrary output
of an external command, which you do not control.  It could easily
contain substrings that are meaningful to "print".

To insert an empty line in your output, just add an empty element
to "var2" in the desired position.

	% var=(a)
	% var+=
	% var+=b
	% typeset -p var
	typeset -a var=( a '' b )
	% print -rC1 -- "$var[@]"
	a

	b


>         fi
>         var2+="${${=var[i]}[2,-1]}" # Copy the rest of the line no 
> matter how many words.

You should store the result of "${=var[i]}" in a temporary variable
and use that, instead of repeatedly word-splitting the same string
over and over and over.


>     done
>        
>     print -l "$var2[@]"

Use "print -r" to prevent "print" from interpreting escape sequences
in its arguments.

As I mentioned in a previous email, if "var2" has no elements,
"print -l" will print one empty line anyway.  Use "print -C1"
instead.

	print -rC1 -- "$var2[@]"


-- 
vq