P1
P1 is a local symbol created automatically for the first parameter passed to a command procedure. Other such symbols include P2, P3, P4, P5, P6, P7, and P8.
Example
Consider the following command procedure named TEST.COM:
$ show sym P1
This will display whatever values we pass as the first parameter to the command procedure:
$ @TEST 1 P1 = "1"
$ @TEST Hello P1 = "HELLO"
$ @TEST "Hello" P1 = "Hello"
$ @TEST P1 = ""