This script will try to determine a list of members of the given group and list all members (macOS)

allusers.sh

#!/bin/bash

export PATH=/usr/bin:/bin:/usr/sbin:/sbin

# allusers.sh
#
# written by Armin Briegel, Scripting OS X, 2018
#
# code is provided as is, with no guarantees that it will work etc.
# adapt and use as you will
#
#/ lists all users on macOS for given group
#/
#/ usage:
#/     allusers.sh groupname [node]
#/         - groupname: short name for the group to list users for
#/         - node: directory node path to search for user
#/                 defaults to /Local/Default
#/ 

usage() {
    grep '^#/' "$0" | cut -c4-
    exit 0
}

groupmembers() { # $1: groupname
    # get group members
    members=$(dscl "$node" read /Groups/"$1" GroupMembership 2>/dev/null )
    
    if [[ "$members" == GroupMembership* ]]; then
        members=${members:17}
    else
        members=""
    fi
    
    #echo "Group: $1, members: $members"
    
    userlist+=' '$members
    
    # recurse with NestedGroups
    nested=$(dscl "$node" read /Groups/"$1" NestedGroups 2>/dev/null )
    if [[ "$nested" == NestedGroups* ]]; then
        nested=${nested:14}
    else
        nested=""
    fi
    
    for uuid in $nested ; do
        gname=$(dscl /Search list /Groups GeneratedUID | awk '$2 == "'$uuid'" {print $1;}')
        
        # warn on calculated Groups
        if [[ "$calculatedgroups" == *"$gname"* ]]; then
            >&2 echo "WARNING: '$gname' is a calculated group and cannot be resolved by this script"
            # but keep going
        else        
            groupmembers "$gname"
        fi
    done
}

# first see if $1 is valid
if [[ -z "$1" ]]; then
    usage
    exit 1
fi

group="$1"

if ! dscl /Search read /Groups/"$group" 1>/dev/null 2>&1; then
    echo "no group named $group"
    usage
    exit 1
fi

node=${2:-"/Local/Default"}

# get a list of calculated groups, from the local directory only
calculatedgroups=$(dscl "/Local/Default" list /Groups Comment | awk '/calculated/ { print $1; }')

# warn on calculated Groups
if [[ "$calculatedgroups" == *"$group"* ]]; then
    >&2 echo "WARNING: '$group' is a calculated group and cannot be resolved by this script"
    exit 1
fi

# get gid for group
gid=$(dscl "$node" read /Groups/"$group" PrimaryGroupID | cut -d ' ' -f 2)

#echo "gid: $gid"
# get users matching PrimaryGroupID
gidusers=$(dscl "$node" list /Users PrimaryGroupID | awk '$2=='"$gid"' { print $1; }')

userlist=$gidusers

# get group members
groupmembers "$group"

# replace whitespace with new line, sort and uniquify
echo "$userlist" | tr -s '[:space:]' $'\n' | sort | uniq