make_joker_user.sh

#!/bin/sh -e

NEW_USERNAME=joker

test -n "$NEW_USERNAME"
command -v sudo >/dev/null
test -x /bin/bash

adduser --shell=/bin/bash -- "$NEW_USERNAME"
adduser -- "$NEW_USERNAME" sudo

NEW_HOMEDIR="$( getent -- passwd "$NEW_USERNAME" | cut -d: -f6 )"
test -n "$NEW_HOMEDIR"
cd -- "$NEW_HOMEDIR"

chown_and_mod() {
    chown -- "$NEW_USERNAME:$NEW_USERNAME" "$2"
    chmod -- "$1" "$2"
}

NEW_SSHDIR="$NEW_HOMEDIR/.ssh"

mkdir -- "$NEW_SSHDIR"
chown_and_mod 700 "$NEW_SSHDIR"

NEW_AUTHKEYS_FILE="$NEW_SSHDIR/authorized_keys"

IFS= read -p 'Enter a new entry for authorized_keys file: ' PUBKEY_LINE
printf '%s\n' "$PUBKEY_LINE" >> "$NEW_AUTHKEYS_FILE"
chown_and_mod 600 "$NEW_AUTHKEYS_FILE"