How to Create a Custom Passwd script - LINUX

We have a Centos 7 machine whereby we need to add a lot of NoLogin passwd entries such as:

username:!!:1010:1001:1stName LastName:/home/username/:/sbin/nologin

We have a CSV list of the new users in the following format:

username,UID,1stName,LastName

Please help me find a way to create a user passwd entry that inserts the username,UID, 1stName LastName, Home Directory/username with the nologin suffix Thanks, Robert

Something like...

#!/bin/sh
  
# example pass.txt contains...
# username,UID,1stName,LastName
# john,1111,dave,smith
# colin,2222,henry,north
# freda,3333,susan,doig

if test $# -eq 1  && test "${1}" = "-u"
then
        # Use userid in file
        Do_UID_File=1
else
        Do_UID_File=0
fi

IFS=,

while read username UIDnum FirstName LastName
do
        # echo "User name is ${username}, UID is ${UIDnum}, 1st name is ${FirstName}, last name is ${LastName}"

        $(id "${username}" > /dev/null 2>&1)
        if test $? -eq 0
        then
                echo "Failed to add ${username}, UID is ${UIDnum}, 1st name is ${FirstName}, last name is ${LastName} - username already exists"
        else
                $(id "${UIDnum}" > /dev/null 2>&1)
                if test $? -eq 0
                then
                        # UID in use
                        if test ${Do_UID_File} -eq 0
                        then
                                # UID in use and do not use UID in file
                                useradd -m -N -s /sbin/nologin "${username}" 1
                        else
                                # UID in use and do use UID in file
                                echo "Failed to add ${username}, UID is ${UIDnum}, 1st name is ${FirstName}, last name is ${LastName} - user ID already exists" 2
                        fi
                else
                        # UID not in use
                        if test ${Do_UID_File} -eq 0
                        then
                                # UID not in use and do not use UID in file
                                useradd -m -N -s /sbin/nologin              "${username}" 3
                        else
                                # UID not in use and do use UID in file
                                useradd -m -N -s /sbin/nologin -u ${UIDnum} "${username}" 4
                        fi
                fi
        fi
done < pass.txt

As always, check, check, then check again.