[thelist] shell script issues

[Dan McCullough]

I keep getting a "expr: syntax error" on this one shell script I am writting.
basically here is the section that is giving me the problem.

code:
PID=`ps -aef | grep Xms128m | grep -v grep | gawk '{print $2}'`
PID=`expr $PID + 1 - 1`
output: 
expr 20265 20292 20314 20342 + 1 - 1

I need some help in fixing this so it works.  anyone have a suggestion or two?