Create a new field using other field values concatenated

[scout29]

I am trying to create a new field called "description" that contains values from two other existing fields. 

If field "app" is equal to linux than i want to combine existing fields "host" and "alert_type".

If field "app" is equal to windows than i want to combine existing field values "host" and "severity"

If app equals anything else, i want the value to be false. 

Below is the eval i have, buts its not working:

| eval description=if('app'=="linux", host. "-" .alert_type',  'app'==windows, host. "-" .severity, "false")

[dural_yyz · Accepted solution]

| eval description=if('app'=="linux", host. "-" .alert_type',  'app'==windows, host. "-" .severity, "false")

You didn't nest the second IF statement

| eval description=if('app'=="linux", host. "-" .alert_type',if('app'==windows, host. "-" .severity, "false"))