Code:

if [[ 'grep -c "$username" /etc/passwd' = "1" ]]

'grep -c "$username" /etc/passwd' will never equal "1", because it's a string, containing the letters grep -c "$username" /etc/passwd". Single-quotes never run what's inside them.

Even if you did run it by putting it in backticks instead of single quotes, you'd still be doing it rather the long way around, making it count and checking its output string instead of just checking the return value grep and any other shell program gives you every time they finish. If grep succeeds, it'll trigger like 'true' in an if-statement, if it fails, it'll be like 'false'.

How about:

Code:

if grep -q "^$username:" /etc/passwd
then
...
fi

The "^" at the beginning of the string has a special meaning to grep, "must start at the beginning of the line". The : at the end just means :, so we know it matched the entire username part of "username:x:uid:gid:..." and not just part of it like "usernamezzz:x:uid:gid:..."

---------- Post updated at 05:05 PM ---------- Previous update was at 04:54 PM ----------

You also don't need to nest things 9 if-statements deep to check more than one thing in a row. Do that for more than 3 things and your code will become unreadable. If something's wrong, just quit early and spare yourself the mess.

You shouldn't depend on the $HOME variable. In some situations that's not even set. Try UID, that'll be 0 for root.

Code:

function die
{
        echo "$@" >&2
        exit 1
}

[ "$UID" -eq 0 ] || die "Not root"
[ -f /etc/passwd ] || die "/etc/passwd missing"

read USERNAME

until [ "$USERNAME" = "done" ]
do
        if grep -q "^${USERNAME}:" /etc/passwd
        then
                ...
        else
                echo "$USERNAME not found"
        fi

        read USERNAME
done