Script users

mirror25 · 03-02-2019, 09:14 AM

Good morning, I have a problem with the following shell script.
Do I need to ask again if the user is already registered in the system? If I put a pause after <echo "already exists"> it gives me an error, and if I put an output, it leaves the script completely. I've also tried to put a real one after <echo -n "Do you want to enter a user? (Y / N):"; read answer> but it does not work either

The purpose of the script is to request a username, if it does not exist, and then create it. But if it already exists ask for another name.

Thank you.

#! / bin / bash
echo -n "Do you want to enter a user? (s / N):"; read answer

yes [$ answer = 's']; so
echo "Enter the user:"
read USER
if grep -qi "^ $ USER:" / etc / passwd
so
echo "already exists"
plus
echo "does not exist"
fi
elif
[$ answer = 'N']; so
exit
fi

Turbocapitalist · 03-02-2019, 09:25 AM

Welcome.

There are extra spaces in your grep query. Also, can you click on the Edit button for your post above and insert [code] [/code] tags so that the indentation is preserved. It will be much more readable then.

BW-userx · 03-02-2019, 09:33 AM

Your use of the words. 'so' + 'plus',

Code:

if [ true ] ; then
echo "hello world"
else
echo "good-bye world"
fi

Actually, your code is a complete cabash...

Bash Guide for Beginners

mirror25 · 03-02-2019, 09:44 AM

Good morning, I have a problem with the following shell script.
Do I need to ask again if the user is already registered in the system? If I put a pause after <echo "already exists"> it gives me an error, and if I put an output, it leaves the script completely. I've also tried to put a real one after <echo -n "Do you want to enter a user? (Y / N):"; read answer> but it does not work either

The purpose of the script is to request a username, if it does not exist, and then create it. But if it already exists ask for another name.

Thank you.

Code:

#!/bin/bash
echo -n "Do you want to enter a user? (y/N): "; read answer

 if [ $answer = 'y' ]; then
   echo "Enter the user: "
    read USER
	if grep -qi "^$USER:" /etc/passwd 
	then 
	echo "already exists" 
	else 
	echo "does not exist" 
	fi 
 elif
     [ $answer = 'N' ]; then
 exit 
fi

1nuxg33k · 03-02-2019, 09:45 AM

Additionally to check your code https://www.shellcheck.net/

Turbocapitalist · 03-02-2019, 09:58 AM

One problem will be hard to spot: Uppercase variables will often reserved by the system and in those cases they are immutable. The variable $USER is one of them, the system fills that one in for you and you can't change it. Try putting "echo $USER;" at the top of your script on the line after the shebang. In general it is good practice to make all your variables lowercase and if you make your script variable lowercase, $user, then you can avoid the problem with $USER.

michaelk · 03-02-2019, 10:00 AM

For your information.
The standard convention of (y/N) is if nothing was entered i.e. just the enter key was pressed the default input is n or N. You also should check to see if Y was pressed too.

BW-userx · 03-02-2019, 10:36 AM

Quote:

Originally Posted by mirror25

Good morning, I have a problem with the following shell script.
Do I need to ask again if the user is already registered in the system? If I put a pause after <echo "already exists"> it gives me an error, and if I put an output, it leaves the script completely. I've also tried to put a real one after <echo -n "Do you want to enter a user? (Y / N):"; read answer> but it does not work either

The purpose of the script is to request a username, if it does not exist, and then create it. But if it already exists ask for another name.

Thank you.

Code:

#!/bin/bash
echo -n "Do you want to enter a user? (y/N): "; read answer

 if [ $answer = 'y' ]; then
   echo "Enter the user: "
    read USER
	if grep -qi "^$USER:" /etc/passwd 
	then 
	echo "already exists" 
	else 
	echo "does not exist" 
	fi 
 elif
     [ $answer = 'N' ]; then
 exit 
fi

or

Code:

#!/bin/bash
#echo -n "Do you want to enter a user? (y/N): "; read answer

#default setting to N as indicated in message, so if user hits enter
#it automatically 'defaults' to N
answer=N
#eliminate echo command 
read -p "Do you want to enter a user? (y/N)" answer

     #no longer case sensitive. 
	case $answer in 
	'Y'|'y')
	read -p "Enter the user name: " user
	#USER reserved word
	#read  USER
	               #check substring
	if [[ $(grep "$user" /etc/passwd) =~ "$user" ]] ; 
	then 
	echo "$user already exists" 
	else 
	echo "$user does not exist" 
	exit
	fi 
	;;
	'N'|'n')
	echo "C'ya!"
	exit 
	;;
	esac

now you can move on to your next step,

'if it (user name) does not exist, and then create it. But if it already exists [then] ask for another [different] name.

you are going to need a loop maybe two. study up on loops.

A word on order and logic

mirror25 · 03-02-2019, 11:04 AM

But how should I do it to ask again the name of the user if it already exists. I do not know how to create the loop.

BW-userx · 03-02-2019, 11:19 AM

Quote:

Originally Posted by mirror25

But how should I do it to ask again the name of the user if it already exists. I do not know how to create the loop.

this is NOT a fully working script, IT has buggs in it, and not the bunny kind. SO you can examine it and analyze buggy code to fix it, so hopefully you'll gain the know how to understanding code, even bash scripting.

Code:

#!/bin/bash
#echo -n "Do you want to enter a user? (y/N): "; read answer
set -xv

#default setting to N as indicated in message
answer=N
go=p

read -p "Do you want to enter a user? (y/N) " answer

while [[ go != 'dn' ]] ;
do

	case $answer in 
	'Y'|'y')
	
	#check for epmty is y then get it filled
	#prevents from asking again in loop
	[[ ! -n "$user" ]] && { read -p "Enter the user: " user ; }
	#if user not present create user
	while [[ ! $(grep "^$user" /etc/passwd) =~ "$user" ]] ; 
	do
		sudo adduser
	read -p "Do you want to add another user? (y/N) " answer
	[[ "${answer,,}" = "n" ]] && { exit ; } || { unset user ; continue ; }
	done
	
	#if user present 
	while [[ $(grep "^$user" /etc/passwd) =~ "$user" ]] ;
	do
		read -p  "$user is already present in system. 
Please enter a different user name " user
			break
	done
	
	;;
	'N'|'n')
	echo "C'ya!"
	exit 
	;;
	esac
	
	
done

please read up on loops
basic understanding of loops in itself
https://www.tutorialspoint.com/cprogramming/c_loops.htm
and bash loops
https://ryanstutorials.net/bash-scri...bash-loops.php
and
http://tldp.org/HOWTO/Bash-Prog-Intro-HOWTO-7.html

P.S.
some of this code may not even be needed.

Turbocapitalist · 03-02-2019, 11:25 AM

The pattern should be delimited so that a partial match does not trigger a false response:

Code:

grep "^$user:" /etc/passwd)

The colon : is needed there for that.

grail · 03-03-2019, 02:05 AM

Plenty of good points covered and to be worked on, I would say that as a beginner in bash scripting this can be a very good introduction as it covers a number of techniques and easy gotchas.

First idea for me would be to get it clear in my head what the question is (my understanding):

Create a user based on name presented by the user. Should the name exist, ask for an alternative

Straight away the above leaves me with some questions:

- Create a user -- would generally mean being root/super user, do we have access to do this?

- based on name presented by the user -- are there any restrictions (ie length) or any particular format (lastname + first initial, etc)

- ask for an alternative -- how many times? ie. is there a set limit or do we expect the user to try until the task is completed

- After the successful creation of one user, should the script exit or prompt to possibly create more?

- Will we need to deal with assigning a password (albeit a default)? (again super user access required)

Now assuming we have acceptable answers to the above, we still need to look at the fact we are dealing with humans (always an issue)
So some basic questions based on the current examples provided:

- Does the user running the script have the permissions to read the necessary files? (/etc/passwd, if not, do they get an error or exit gracefully with a message to contact the admin?)

- Are we going to allow the user to correct the name if they make a typo?

- If presenting the user with questions with expected results, ie. yes / no questions, what checking is to be done on wrong input?

Using yes/no as example:

- Are we requiring full word, yes or no
- Are we limiting to the first letter? (if so, what if they enter "p")
- If limiting to the first letter, are we taking control to a single key pressed? (ie. after key press the answer is submitted without needing enter key, this alleviates the issue of user pressing more than one key (with some caveats))

My final thought would be, are we going to limit ourselves to only bash builtins (excluding creating user and password)? (ie. no grep/sed/awk, to name a few)
The above can make it a little more interesting as now you need a function to read through /etc/passwd file to check for existing users

So whilst a relatively simple task, I see this as a good learning experience

--- Good luck

orbea · 03-03-2019, 09:16 AM

Quote:

Originally Posted by Turbocapitalist

The variable $USER is one of them, the system fills that one in for you and you can't change it.

Code:

$ echo $USER
orbea
$ USER=foo
$ echo $USER
foo

Turbocapitalist · 03-03-2019, 09:26 AM

Quote:

Originally Posted by orbea

Code:

$ echo $USER
orbea
$ USER=foo
$ echo $USER
foo

Thanks for catching that. I mis-remembered or else, most unlikely, things changed. Now that I check, $USER can be modified as can $LOGNAME. However, UID and EUID are read-only variables:

Code:

readonly | awk '{sub(/=.*$/,"",$3); print $3}'

orbea · 03-03-2019, 10:00 AM

Neat command, I didn't know I could check that so easily.

Code:

$ readonly | awk '{sub(/=.*$/,"",$3); print $3}'
BASHOPTS
BASH_VERSINFO
EUID
PPID
SHELLOPTS
UI

That is with bash-5.0.002 and this seems highly dependent on the specific shell and not all of them have readonly variables.

mksh/pdksh

Code:

$ readonly
KSH_VERSION

mksh the second time 'readonly' is used.

Code:

$ readonly                                                                       
KSH_VERSION
PIPESTATUS[0]

openbsd ksh

Code:

$ readonly
KSH_VERSION
PPID

posh

Code:

$ readonly
POSH_VERSION

zsh

Code:

% readonly                                      
'!'=0
'#'=0
'$'=8458
'*'=(  )
-=569XZims
'?'=130
@=(  )
ARGC=0
HISTCMD=4
LINENO=4
PPID=8457
TTYIDLE=3
ZSH_EVAL_CONTEXT=toplevel
ZSH_SUBSHELL=0
status=130
zsh_eval_context=( toplevel )

I also tried Slackware's (Old) ash, dash, ksh and yash which returned nothing with 'readonly'.