grabbing the newest file from a subset of the contents of a folder in bash - bash

Question

I have a folder with such contents
nass#starmaze:~/audio_setup/scripts$ ls -l ../jmess/
total 32
-rw-rw-r-- 1 nass users 1573 Νοέ 16 2014 jmess_fxio56-78feedsHDA-play12.jmess
-rw-rw-r-- 1 nass nass 1573 Δεκ 13 2014 jmess_pb-2.jmess
-rw-rw-r-- 1 nass nass 1573 Δεκ 20 2014 jmess_pb-3.jmess
-rw-rw-r-- 1 nass nass 1939 Ιούν 12 13:05 jmess_starmazeOnMaster.jmess
-rw-rw-r-- 1 nass nass 2163 Δεκ 15 2014 jmess_starmazeOnMaster.jmess.bak1-art
-rw-rw-r-- 1 nass nass 2161 Δεκ 15 2014 jmess_starmazeOnMaster.jmess.bak2-bcr
-rw-rw-r-- 1 nass nass 2389 Δεκ 22 2014 jmess_starmazeOnMaster.jmess.bak3-hoo
-rw-rw-r-- 1 nass nass 2163 Δεκ 15 2014 jmess_starmazeOnMaster.jmess.bak4-dsp
I want to be able to pick up the newest file, but only from the subset of files that do not contain the word "Master" in them. And I want to put that in a bash script.
So this
ls -t1 "${JCMESS_FOLDER}" | head -n1
provides the newest file in the folder , while this
ls -t1 "${JCMESS_FOLDER}"/!(*Master*) | head -n1
provides the newest file among the subset that I am interested in.
However, when I place the latter in a bash script as
$NEWEST_JCMESS_FILE=$( ls -t1 "${JCMESS_FOLDER}"/!(*Master*) | head -n1 )
it does not work:
./06.load_jcmess: command substitution: line 8: syntax error near unexpected token `('
./06.load_jcmess: command substitution: line 8: ` ls -t1 "${JCMESS_FOLDER}"/!(*Master*) | head -n1 )'
I am not sure what is wrong in this case and I ahve not been able to successfully find an answer for this.
thank you in advance for your help

Answer 1

This is BashFAQ #3:
newest() {
local candidate result=$1; shift # start with first argument as candidate
[[ -e $result ]] || return # handle case where nothing matched
for candidate; do # for loop default behavior is to loop over "$#"
[[ $candidate -nt $result ]] && result=$candidate
done
printf '%s\n' "$result"
}
shopt -s extglob # enable extglobs, ie. !(...)
newest_file=$(newest "$JCMESS_FOLDER"/!(*Master*))