1 
#!/bin/bash

echo "Type in your username in lowercase letters"
read user
#sudo adduser $user

echo "Are you a student or teacher?"
read group

if (("$group"=="teacher"));
then
        #sudo usermod -aG teachers
        echo "teacher"

elif (("$group"=="student"));
then
        #sudo usermod -aG students
        echo "students"
else
        echo "Sorry this group doesn't exist"
fi

I'm trying to make a shell script that allows me to create a user and then automatically add it into a group that they want to be in. The input is either a student or a teacher although i want to include these statements above but i can't seem to make it work because it just goes to to the 'if' statement and ignores if i use the input student.

Could you please help me with this problem?

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4 Answers 4

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3

try 

if [ "$group" = teacher ]

mind

  • space arround [ and ]
  • = (no need for ==)
  • no semicolon

instead of 

if (("$group"=="teacher"));
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0
1

IMO case is a better match for this task than if/elif/else/fi. For example:

case "$group" in 
    teacher)  echo teacher ; sudo usermod -aG teachers ;;
    student)  echo student ; sudo usermod -aG students ;;
    *) echo "Sorry, this group doesn't exist" ; exit 1 ;;
esac

Note that wildcards can be used:

    te*)  echo teacher ; sudo usermod -aG teachers ;;
    st*)  echo student ; sudo usermod -aG students ;;

that will match any group entered beginning with te or st.

BTW, instead of running sudo multiple times in the script, you're better off writing the script so that it first gets the input from the user, then validates/sanitises it, and only then runs sudo once to perform the required actions. If necessary, write a second script that does ONLY the adduser and usermod stuff based with the args passed on the command line, and only allow that script to be run by sudo.

For example:

#! /bin/sh

read -p "Type in your username in lowercase letters: " user
grep -q "^$user:" /etc/passwd && echo "Sorry, that user already exists" && exit 1

read -p "Are you a student or teacher? " group

[[ "$group" ~ student|teacher ]] || echo "Sorry, no such group" && exit 1

sudo useradd "$user" -G "$group"

but it's hard to see the point of this script when you can just do it all on the command line with sudo useradd user -G group without wasting time with prompts and answering questions.

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1

In bash, this:

if (("$group"=="teacher"));

is a numeric test of the variables. The variables are evaluated as numbers, and if they contain only text, they evaluate to 0.

The correct test for text in bash is:

if [[ $group == teacher ]];

no need for quotes in this case (not always) and you can use == or = (which are equivalent inside [[).

For POSIX shells you need to use:

if [ "$group" = "teacher" ];

You do need to use simple [, quote the variable, and use the =.

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-1 
#! /bin/bash
echo "Type your username in lowercase letters"
read user
echo "Are you a student or teachers or other"
read group
if [ $group == student ]
then
useradd $user && usermod -aG student $user
echo "sucessfully added to student"
elif [ $group == teachers ]
then
useradd $user && usermod -aG teachers $user
echo "sucessfully added to teachers"
else [ $group == other ]
echo " sorry "
fi
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2
  • 1
    Welcome to Unix & Linux! Brevity is acceptable, but fuller explanations are better. Commented Aug 26, 2021 at 14:56
  • 1
    within [ .. ], you need quotes around the variable expansion to avoid issues with white space, and also = is the standard equality comparison. While == works in Bash and ksh, it doesn't in e.g. Dash, and it causes problems in zsh, and there's little reason for using it. Also, your code would be clearer if you indented it properly. And then there's the thing that I'm not sure if this answer gives anything on top of the previous ones. Commented Aug 26, 2021 at 17:11

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