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Create users using bash script


You appear to have written your script in a word processor that have capitalized words that shouldn’t be capitalized (command names ar case sensitive on Unix), and used fancy typographical double quotes (“...” instead of "..."). Do consider writing your scripts in a simpler text editor such as nano, emacs or vim. The site https://www.shellcheck.net/ is very helpful for spotting simpler errors in scripts.

Take that as a hint that all command names should be lower-case and that you need to change the quotes.

Your loop is also a bit strange. On one hand you seem to want to loop over { $num } (which I don’t know what it means), and on the other you increment num inside the loop. Note that num is the number inputted by the user, so incrementing it makes no sense. Let’s assume that you update the variable in the loop:

while [ "$num" -ne 0 ]; do
   # code here that increments "number",
   # and conditionally decrements "num"

Remember that you have to keep track of the number used in the username as well as the number of created users. You need to do this to know both when you have created the correct number of users, and to be able to skip usernames that are already existing on the system. Here I’m choosing to decrement num until it reaches zero, while keeping the number used in usernames in the variable called number.

Inside the loop, you will have to try to create user $pre$number, and if that succeeds, you decrement num. In each iteration, you then always increment number. You iterate until num reaches zero, which means that you have created all the users.

Assuming that adduser returns a sane exit status for succeeding and failing (note: I’m not a Linux user, so I don’t know what happens on CentOS if you try to create an already existing user), you could add a user using

if adduser -m "$pre$number"; then
    # adduser succeeded, we've created a new user, decrement num
    num=$(( num - 1 ))
number=$(( number + 1 ))

Or, you could check whether the proposed username exists first using getent:

if ! getent passwd "$pre$number" >/dev/null; then
    # the user don't exist, create it
    adduser -m "$pre$number"
    num=$(( num - 1 ))
number=$(( number + 1 ))

The getent passwd command will fail if the given username does not exist on the system. We use this fact here to avoid calling adduser with an existing username.

I’ll ignore most of the code in the beginning of your script, but I’ll just point out that declaring num as integer is not needed, and that read -p 'prompt' var reads a value from the user with a specific prompt, so the echo statements are not needed.

You may also want to consider the fact that the $pre string in your code actually is accepted even though it may not be the string student or user (as the output from you current code suggests that it should be).

You should also account for the case where $pre may be invalid in a username, for example, when it contains a space. Depending on how you write the code, and if you don’t check that $pre$number is as a username, this may mean failing to create any accounts, or trying to create an infinite number of accounts.

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