How to check if the /etc/passwd file in Linux contains invalid entry?

I am trying to determine if the passwd file present in the location /etc/passwd in Linux contains any invalid data entries with the pwck command.

For example:
1) If my file contains this entry which is invalid due to the extra colon in the end - user1:x:1000:1000:user1,,,:/home/user1:/bin/bash:

sudo pwck -r /etc/passwd

This takes a no by default if invalid entries exist and shows other output as well

2) If my passwd file is correct syntactically but has user that does not have corresponding directories

sudo pwck -r /etc/passwd

user 'user1': directory '/var/xyz' does not exist

The exit values of both commands is 2 so I cannot distinguish if the user entry is invalid or there are directories for users that are non existent

I only want to identify an invalid entry in passwd file i.e if there is some extra character or syntactically wrongly added entry in the file

Solution

If you want only the "syntatic" correctness, just write a regex to match it. Reading from wikipedia and shadow sources to match the user name right, I wrote this for GNU sed:

sed -r '/^[a-z_][a-z0-9_-]*[$]?:[^:]*:[0-9]+:[0-9]+:[^:]*:[^:]*:[^:]*$/!q1'

But there are many other checks that pwck does.

So I think the best way would be to take pwck sources and hand-pick the checks you are interested in and remove the checks you are not interested in.

so I cannot distinguish

Sure you can distinguish - as the program outputs what is wrong with the file.

if ! out=$(sudo pwck -r /etc/passwd 2>&1); then
   if <<<"$out" grep -q 'invalid user name\|invalid user ID\|invalid password file entry'; then
       echo "File is syntactically wrong"
   else
        echo "Something else is wrong with the file"
   fi
fi