o word if the expanded value of param is unset or null, and $param otherwise.
To use negative offsets... Example
${foo:-bar} If $foo exists and is not null, return $foo. If it doesn't exist or is null, return bar. export foo=""
echo ${foo:-one}
one
echo $foo
${foo:=bar} If $foo exists and is not null, return $foo. If it doesn't exist or is null, set
n of this comparison operator.
----
-z
string is null, that is, has zero length
<code>
String='' # Zero-length ("null") string variable.
if [ -z "$String" ]
then
echo "\$String is null."
else
echo "\$String is NOT null."
fi # $String is null.
</code>
----
-n
string is
