Windows 'sh' command not found while running grails

I'm running grails and when i ran `grails clean-app' I got the error. Even if I run 'sh' command it says command not found. I know it's realted to my environment variable path issue but which path I need to set for 'sh' command ?

| Environment set to development....
Sencha Command: cleaning web assets...
| Error Error executing script Clean: java.io.IOException: Cannot run program "r
m": CreateProcess error=2, The system cannot find the file specified (NOTE: Stac
k trace has been filtered. Use --verbose to see entire trace.)
java.io.IOException: Cannot run program "rm": CreateProcess error=2, The system
cannot find the file specified
        at _Events$_run_closure3.doCall(_Events.groovy:83)
        at _GrailsClean$_run_closure1.doCall(_GrailsClean.groovy:37)
        at org.codehaus.gant.GantMetaClass.invokeMethod(GantMetaClass.java:133)
        at org.codehaus.gant.GantBinding$_initializeGantBinding_closure5_closure
16_closure18.doCall(GantBinding.groovy:185)
        at org.codehaus.gant.GantBinding$_initializeGantBinding_closure5_closure
16_closure18.doCall(GantBinding.groovy)
        at org.codehaus.gant.GantBinding.withTargetEvent(GantBinding.groovy:90)
        at org.codehaus.gant.GantBinding.this$4$withTargetEvent(GantBinding.groo
vy)
        at org.codehaus.gant.GantBinding$_initializeGantBinding_closure5_closure
16.doCall(GantBinding.groovy:185)
        at org.codehaus.gant.GantBinding$_initializeGantBinding_closure5_closure
16.doCall(GantBinding.groovy)
        at gant.Gant$_dispatch_closure5.doCall(Gant.groovy:381)
        at gant.Gant$_dispatch_closure7.doCall(Gant.groovy:415)
        at gant.Gant$_dispatch_closure7.doCall(Gant.groovy)
        at gant.Gant.withBuildListeners(Gant.groovy:427)
        at gant.Gant.this$2$withBuildListeners(Gant.groovy)
        at gant.Gant$this$2$withBuildListeners$0.callCurrent(Unknown Source)
        at gant.Gant.dispatch(Gant.groovy:415)
        at gant.Gant.this$2$dispatch(Gant.groovy)
        at gant.Gant.invokeMethod(Gant.groovy)
        at gant.Gant.executeTargets(Gant.groovy:591)
        at gant.Gant.executeTargets(Gant.groovy:590)
Caused by: java.io.IOException: CreateProcess error=2, The system cannot find th
e file specified
        ... 20 more
| Error Error executing script Clean: java.io.IOException: Cannot run program "r
m": CreateProcess error=2, The system cannot find the file specified