Need explanation for the syntax(code)

Shell Programming and Scripting
1

Hi I am new to shell script programming...
want to know the process of the following:

if[ -n "$MISSINGOPTARG"]
then
echo "$0: missing argument for option(s) :$MISSINGOPTARG"
echo "usage" $USAGE"
exit 1
fi

2

-n "$MISSINGOPTARG"
-n option checks whether $MISSINGOPTARG contain any text in it.

You have to use -z option to check whether $MISSINGOPTARG is empty and if it is empty then condition -z "$MISSINGOPTARG" is true

if[ -z "$MISSINGOPTARG" ]
then
   echo "$0: missing argument for option(s) :$MISSINGOPTARG"
   echo "usage" $USAGE"
   exit 1
fi