If / Else statement issues in bash scripting - bash

Question

I recently created a different thread with an issue concerning a for loop in a bash script I was writing for my GCSE coursework. I have another issue with the same bash script (however it has evolved a fair bit since last time).
Here is the code:
#!/bin/bash
# A script that creates users.
uerror='^[0-9]+$'
echo "This is a script to create new users on this system."
echo "How many users do you want to add? (in integer numbers)"
read am
echo " "
if [[ $am =~ $uerror ]] ; then
echo "ERROR: Please use integer numbers."
echo "Please re-enter the amount."
read am ;
else
echo " "
for i in $(seq "$am")
do
echo "Enter a username below:"
read usern
sudo useradd $usern
sudo passwd $usern
echo " "
echo "User $i '$usern' added."
echo " "
echo "What group do you want to add $usern to?"
read group
sudo usermod $usern -aG $group
echo "$usern added to $group"
echo " "
echo "-------------------"
echo " "
done
fi
The issue is in the if statement. It's purpose is to stop users entering anything other than an integer number. But for some reason, I don't seem to be able to capture the input from the read am part. Instead the script skips straight onto the for loop where the $(seq "$am") obviously will have issues comprehending an input that is not a number.
The output from this error is as follows.
seq: invalid floating point argument
However, I don't think this is relevant because as far as I can tell, the issue is with the if / else statement.
If anyone could point me in the right direction of what I need to do to fix this, I would be greatly appreciative.
I'd also like to iterate that I am still learning how to write bash scripts (and not in a particularly organised manner) so I've probably made a very simple mistake. Apologies for that.
Thanks,
Callum.
EDIT: I mistyped an echo message, I've now changed that so it actually makes sense.

Answer 1

If you want to read in a number and make sure it is a number use a while loop:
while read -p 'type a number:' n ; do
# Exit the loop if the input is a number
[[ "$n" =~ ^[0-9]+$ ]] && break
echo "This was not a number! Don't trick me!"
done
# Now can use `seq`
seq "$n"
The if statement in your example would do the completely the wrong thing. It checks if the input is a number and in that case asks for the input again and exits the script. If you don't type a number, it uses the (wrong) input in the else branch.

Answer 2

Replace your whole file with this:
#!/bin/bash
# A script that creates users.
uerror='^[0-9]+$'
echo "This is a script to create new users on this system."
echo "How many users do you want to add? (in integer numbers)"
read am
echo " "
while true; do
if [[ $am =~ $uerror ]] ; then
break;
else
echo "Must be integer"
echo "Please re-enter: "
read am ;
fi
done
for i in $(seq "$am")
do
echo "Enter a username below:"
read usern
sudo useradd $usern
sudo passwd $usern
echo " "
echo "User $i '$usern' added."
echo " "
echo "What group do you want to add $usern to?"
read group
sudo usermod $usern -aG $group
echo "$usern added to $group"
echo " "
echo "-------------------"
echo " "
done