Re: How do we get state of a flag in set -o ...

[Greg Wooledge]

On Tue, Jul 11, 2023 at 11:49:40PM +0200, alex xmb ratchev wrote:
> set -- opt1 val1 opt2 val2 ; declare -A conf=( $@ ) ; declare -p conf
>                                                      declare -A
> conf=(["opt1 val1 opt2 val2"]="" )
> 
> >
> i dont get it
> im suure i used this working maany times
> 
> -- why doesnt it split

The parser sees

    conf=( $@ )

Now, the parser is not very bright, so it tries to figure out whether
this command should be parsed as

    conf=( [key]=value )

or as

    conf=( key value )

It makes this decision WITHOUT expanding $@.  It doesn't matter what you
put in $@.  The parser has already decided.

unicorn:~$ unset -v hash; declare -A hash
unicorn:~$ set -- '[key1]=meow' '[key2]=bowwow'
unicorn:~$ hash=( $@ )
unicorn:~$ declare -p hash
declare -A hash=(["[key1]=meow [key2]=bowwow"]="" )

As we can see here, the parser has decided that it's dealing with

    conf=( key value )

where "key" is whatever $@ expands to, and "value" is the empty string,
because there was no second word after the $@ in the command as it was
parsed.  (And since there were no square brackets.)

Returning to the original question for a moment, the OP's question was
how to determine the state of shell options like 'vi' that have no
single-letter equivalent.  My suggestion was to parse the output of
"set -o".  Another answer was to use test -o vi.

Pursuing my answer for a moment, we start by looking at the output of
set -o:

unicorn:~$ set -o
allexport       off
braceexpand     on
emacs           off
errexit         off
[...]
vi              on
xtrace          off

So, how would we parse this to determine whether the 'vi' option is on
or off?  Here's one way:

    read -r _ state < <(set -o | grep '^vi')

This will store 'on' or 'off' in the state variable.

The "test -o vi" answer may be better than mine.

All the talk of associative arrays and the   array=( key value ... )
syntax is just a digression.