Check if string is valid username using bash script – Code Example

In this article we will provide you bash script code to check if string is a valid username. A username can have lowercase alphanumeric, underscore and dash. It could be 3 to 15 characters long.

Code Example –

#!/bin/bash
is_valid_username() {
    [[ "$1" =~ ^[a-z0-9_-]{3,16}$ ]] && echo $1
}

# This username is bad
username="tony@ironman"

# regex validation will fail
is_valid_username "$username" || echo "Bad username - $username"

good_username="tony_ironman0"
is_valid_username "$good_username" || echo "Bad username - $good_username"

# Output:
# Bad username - tony@ironman
# tony_ironman0