How to make a full bash script that compares the shadow and the passwd file?

1. I have two files, passwd and shadow
   a. Sort both files
   b. Compare both files line by line
     i. Match on user name output to third file
     ii. If it doesn’t match, output to fourth file
     iii. If user does not match, find which file the user is in
2. Either passwd or shadow
3. If user does not exist in passwd file check /home/test123
4. Also look for home directory on the system, it may not be under /home
5. If home directory exists, please add user
6. Add useradd
7. If home directory does not exist, delete the entry from the shadow file
8. Use userdel (xxx)
9. If home directory exits in another file system besides /home then create user and use home directory in the user entry
   a. Ex. /opt/murad
10. After the changes are done, you have to run your comparison again,
11. Now please use modules in your programming also called subroutines in shell programming and create a module called compare_files
12. Please pass parameters to compare_files
13. Create two modules,
    a. Check file()
      i. Use no match entries are empty
14. Exit
15. Create module subroutines

I have tried comparing them, but that's as far as I can come; I am stuck.

This is what I did so far:

#!/bin/sh password_file=pass.txt password_file_sorted="sorted_$password_file" shadow_file=shadow.txt shadow_file_sorted="sorted_$shadow_file" match_file="match_record.txt" not_match_file="not_match_record.txt" # empty target file cp /dev/null $match_file cp /dev/null $not_match_file # check username is exist in file check_file() { username=$1 file=$2 exit_status=1 # username does not exist in file # read line by line while IFS=: read -r f1 f2 f3 f4 f5 f6 f7 do if [ "$f1" = "$username" ]; then exit_status=0 # username exist in file fi done <"$file" return $exit_status } # create module compare_file compare_file() { file_1=$1 file_2=$2 # read line by line content of file_1 while IFS= read -r line do username=$(echo $line | awk -F: '{print $1}') # check username in file_1 is exist on file_2 check_file "$username" "$file_2" if [ $? -eq 0 ]; then #if user exist, write record to match_record.txt file target_file=$match_file else #if user does not exist, write record to not_match_record.txt file target_file=$not_match_file fi echo $line >>$target_file done <"$file_1" } # short password files echo "short $password_file" sort $password_file > $password_file_sorted # short shadow files echo "short $shadow_file" sort $shadow_file > $shadow_file_sorted # compare file password with shadow echo "check username in $password_file is exist on $shadow_file" compare_file $password_file_sorted $shadow_file_sorted # compare file shadow with password echo "check username in $shadow_file is exist on $password_file" compare_file $shadow_file_sorted $password_file_sorted # add or remove user echo "for every mismatch username in $password_file, add user if home directory exist and remove user if home directory does not exist" while IFS= read -r line do username=$(echo $line | awk -F: '{print $1}') home_directory=$(echo $line | awk -F: '{print $6}') # check user does not exist in passwd num_entries_in_password=$(grep $username $password_file | wc -l) if [ $num_entries_in_password -eq 0 ]; then # check if /home/username directory exist if [ -d "/home/$username" ] ; then echo "/home/$username directory exist, add $username with command: useradd $username" useradd $username elif [ -d $home_directory ]; then # add user with specific user directory echo "$home_directory directory exist, add $username with command: useradd $username -b $home_directory" useradd $username -b $home_directory else echo "remove user: $username" userdel $username fi fi echo "user: '$username' exist in $password_file" done <"$not_match_file" 

The output I am getting is short.  Why is that happening?