Bash script exercise with file

Question

I have this exercise: Create a "groups" BASH shell script, which takes as an argument a groups_file.txt file structured as follows:

adm:x:4:syslog,adm1
admins:x:1006:adm2,adm12,manuel
ssl-cert:x:122:postgres
alan2:x:1009:aceto,salvemini
conda:x:1011:giovannelli,galise,aceto,caputo,haymele,salvemini,scala,adm2,adm12 
adm1Group:x:1022:adm2,adm1,adm3
docker:x:998:manuel

that:

1. prints the maximum number of fields on a line in a given file

2. creates a subdirectory for each group in the file, giving read and write access to users of the groups "adm" and "admins"

3. creates a file for each subdirectory containing the users belonging to that group line by line

I did the first two points but I don't know how to do the last one. I tried to get the groups equal to $1 with awk and then I redirected them to the "$group/user" file but it doesn't work

#!/bin/bash

echo "Stampo il numero massimo di campi di una linea in un dato file: "
cat groups_file.txt | awk -F "[\t,:]" 'NF>6 {print $0}' 

g=$(cat groups_file.txt  | awk -F :  '{print $1}')

for group in $g
do
        mkdir "$group"
        chmod +rwx "$group"
        
        touch "$group"/users 
        chmod +rw "$group"/users
done

Answer 1

You want to read a line at a time and split it on the colons.

A subdirectory can't belong to more than one group, so you have to come up with a separate mechanism for providing read access to more than one group. I simply make it group adm below; a better solution would perhaps be to create a new group with all the members of adm and admins.

I imagine the "maximum number of fields" means to print the line with the highest number of members.

#!/bin/bash

awk -F "[,:]" 'NF>max { maxline = $0; max=NF }
  END { print max, maxline }' groups_file.txt

while IFS=: read -r group pass gid members; do
    mkdir "$group"
    chown "$group":adm "$group"
    chmod 775 "$group"
    echo "${members//,/$'\n'}" >"$group"/users
done <groups_file.txt

Notice also how this avoids the useless use of cat.