Read Command : How to verify user has typed something

Question

I'm trying to create an if else statement to verify that the user has entered something. If they have it should run through the commands, and if not i want to echo a help statement.

Answer 1

An example (fairly easy) is as following. A file named userinput is created which contains the following code.

#!/bin/bash

# create a variable to hold the input
read -p "Please enter something: " userInput

# Check if string is empty using -z. For more 'help test'    
if [[ -z "$userInput" ]]; then
   printf '%s\n' "No input entered"
   exit 1
else
   # If userInput is not empty show what the user typed in and run ls -l
   printf "You entered %s " "$userInput"
   ls -l
fi

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Answer 2

If you want to know if the user entered a specific string, this could help:

#!/bin/bash

while [[ $string != 'string' ]] || [[ $string == '' ]] # While string is different or empty...
do
    read -p "Enter string: " string # Ask the user to enter a string
    echo "Enter a valid string" # Ask the user to enter a valid string
done 
    command 1 # If the string is the correct one, execute the commands
    command 2
    command 3
    ...
    ...

Answer 3

When multiple choices are valid, make a while condition to match regular expression:

For example:

#!/bin/bash

while ! [[ "$image" =~ ^(rhel74|rhel75|cirros35)$ ]] 
do
  echo "Which image do you want to use: rhel74 / rhel75 / cirros35 ?"
  read -r image
done 

It will keep asking for input, until entering one of the three choices.