A little bash function, assigning attributes

Question

This function checks if an attribute has been passed and if not, asks user for input.

I'm new in bash scripting and would like to get some feedback. Is it okay or should I refactor this code somehow to make it more concise?

#!/usr/bin/env bash

fn() {
    if [ -z "$1" ]; then
        read -p "username:" username
    else
        username=$1
    fi

    echo "username is $username"
}

Answer 1

What you're doing is perfectly fine.

If you absolutely want to shorten it (at a slight loss of readability) for whatever reason you could do it this way (at least in bash):

fn() {
    [ -z "$1" ] && read -p "username:" username || username=$1
    echo "username is $username"
}

Output (in a bash environment):

$ fn() {
>     [ -z "$1" ] && read -p "username:" username || username=$1
>     echo "username is $username"
> }
$ fn
username:xx
username is xx
$ fn yy
username is yy
$

Answer 2

Here's an ugly little one-liner:

fn () {
    username=${1:-$(read -p "username:"; echo "$REPLY")}
}

If $1 has a non-null value, that is assigned to username. Otherwise, we read a value and echo it in a command substitution, which captures the echoed value to store in username.