Bash: check user input is correct

Question

Hi there

Im wrote a bash script that takes numbers for calculation via user input, the problem i have is if the user types a letter or a space by mistake the whole script fails and the user must start again.

There must be an easy way to check the input is numeric only that will ask for the input again if anything else is input accidentally.

any help will be much appreciated

thanks

Donaldo

Answer 1

Use a while loop

number=""
while [[ ! $number =~ ^[0-9]+$ ]]; do
    echo Please enter your age
    read number
done
echo You are $number years old

Answer 2

And to avoid the heavy regex engine, use a simple glob:

if [[ $input = *[^0-9]* ]]; then
    echo "Error: '$input' is not a number." >&2
fi