Re: Order of command substitution and arithmetic expansion

[Lawrence Velázquez]

On Sat, Nov 13, 2021, at 2:36 PM, Greg Wooledge wrote:
> So we're left with (b) it goes left to right.

To elaborate a little on what Greg said: Here is the full sentence
from the manual, which you only quoted partially.

    The order of expansions is: brace expansion; tilde expansion,
    parameter and variable expansion, arithmetic expansion, and
    command substitution (done in a left-to-right fashion); word
    splitting; and filename expansion.

The semicolons and colons are not distributed arbitrarily.  You can
think of the sentence as describing the following "precedence":

    1. Brace expansion.
    2. Tilde expansion, parameter and variable expansion, arithmetic
       expansion, command substitution.  These are performed from
       left to right.
    3. Word splitting.
    4. Filename expansion.

The expansions in #2 all have the same "precedence"; the order in
which they are listed doesn't really mean anything.  Observe that,
for instance, a parameter expansion can occur after an arithmetic
expansion:

    $ i=7
    $ echo "$((i++))" "$i"
    7 8

-- 
vq