While Statement help bash scripting : <p>Need help understanding this script I cannot figure out what the <code>-z</code> condition means for first line then the <code>-z</code> with the <code>"$1"</code> in the if statement 
Here is the script:</p>

<pre><code>while [ -z "$USERNAME" ]
do
if [ -z "$1" ]
    then
        unset ans
 unset USER
 echo "What is the username you would like to add?"
 read USER
 echo "Is" $USER " the correct username? [y/n]"
 read ans
 case "$ans" in
     y|Y|yes|Yes|YES)
  USERNAME=$USER
</code></pre>

<p>;;</p>
