help with combining expressions in an if statement

[Jim]

Hi,

I am new to bash and am looking for some help. Specifically, I would 
like to ensure the user supplies two arguments to the shell script - 
month and year. How should I combine multiple expressions in an if 
statement?


So far I have the following script :

month=$1
year=$2

if [ -z$month -o -z$year ]; then
        echo "Usage: $0 month year";
        echo "example: date.sh 01 2005";
        exit 1
fi

In other words I want to say if A is true OR B is true then echo output.

How would I do that?

Any help is much appreciated.

Jim