SUBROUTINE OPN(UNIT,FILE,ACTION,ERR)
	INTEGER UNIT,ERR
	BYTE FILE(1),ACTION,PFIL(40)
	PARAMETER PUICSZ = 9
	DATA PFIL/'S','P','0',':','[','1',',','4',']',31*0/
C
C  OPN - DO OPEN PROCESSING
C           IF ACTION = R THEN OPEN FOR READING
C           IF ACTION = W THEN OPEN FOR WRITING
C           IF ACTION = F THEN OPEN FOR WRITING WITH CARRIAGECONTROL=LIST
C           IF ACTION = A THEN OPEN FOR APPENDING
C           IF ACTION = X THEN OPEN FOR READING WITH DELETE CAPABILITY
C           IF ACTION = P THEN OPEN FOR PRINTING
C
	ERR = 1
	IF (ACTION .NE. 1HR) GOTO 10
	   OPEN(UNIT=UNIT,NAME=FILE,TYPE='OLD',READONLY,SHARED,ERR=99)
	   GOTO 1000
10	CONTINUE
	IF (ACTION .NE. 1HW) GOTO 20
	   OPEN(UNIT=UNIT,NAME=FILE,TYPE='NEW',CARRIAGECONTROL='LIST',
     *          DISPOSE='DELETE',ERR=99)
	   GOTO 1000
20	CONTINUE
	IF (ACTION .NE. 1HA) GOTO 30
	   OPEN(UNIT=UNIT,NAME=FILE,TYPE='UNKNOWN',
     *          ACCESS='APPEND',ERR=99)
	   GOTO 1000
30	CONTINUE
	IF (ACTION .NE. 1HX) GOTO 40
	   OPEN(UNIT=UNIT,NAME=FILE,TYPE='OLD',ERR=99)
	   GOTO 1000
40	CONTINUE
	IF (ACTION .NE. 1HP) GOTO 50
	   I = 0
45	   CONTINUE
	      I = I+1
	      PFIL(I+PUICSZ) = FILE(I)
	      IF (FILE(I) .NE. 0) GOTO 45
	   OPEN(UNIT=UNIT,NAME=PFIL,TYPE='NEW',CARRIAGECONTROL='LIST',
     *          DISPOSE='PRINT',ERR=99)
	   GOTO 1000
50	CONTINUE
	IF (ACTION .NE. 1HF) GOTO 99
	   OPEN(UNIT=UNIT,NAME=FILE,TYPE='NEW',CARRIAGECONTROL='FORTRAN',
     *          DISPOSE='DELETE',ERR=99)
	   GOTO 1000
1000	CONTINUE
	ERR = 0
99	CONTINUE
	RETURN
	END