Reading command line

When a transient command is run from a filing system OSARGS 1,0 can be used to find the command line. This command line is always stored in the I/O processor. Transient commands usually run in the I/O processor so they can read the command line directly using code such as LDA (zp),Y:

   \ lptr    = address in zero page to point to command line
   \ Note, four bytes are read, so lptr+2 and lptr+3 are overwritten
   
   LDA #1:LDY #0:LDX #lptr:JSR OSARGS   :\ Read address of command line
   
   \ (lptr),Y now points to the start of the command's parameters

However, if a transient command is written to run in the language processor it must copy the command line to local memory, or scan it character by character over the Tube. The following code fragments copy the command line to local memory.

6502

   \ addr    = 5-byte buffer in zero page
   \ cmdline = 256-byte buffer to copy command line to
   
   LDA #1:LDY #0:LDX #addr:JSR OSARGS   :\ Read address of command line
   .rdcmdlp
   TYA:PHA
   LDX #addr:LDY #0:LDA #5:JSR OSWORD   :\ Read byte from I/O memory
   PLA:TAY:LDA addr+4:STA cmdline,Y:INY :\ Copy byte to local buffer
   INC addr:BNE rdcmdnxt:INC addr+1     :\ Increment command line address
   .rdcmdnxt
   CMP #13:BNE rdcmdlp                  :\ Loop until <cr>

Z80

   \ addr    = 5-byte buffer
   \ cmdline = 256-byte buffer to copy command line to
   
   LD A,1:LD E,0:LD HL,addr:CALL OSARGS :\ Read address of command line
   LD DE,cmdline
   .rdcmdlp
   LD HL,addr:LD A,5:CALL OSWORD        :\ Read byte from I/O memory
   LD A,(addr+4):LD (DE),A:INC DE       :\ Copy byte to local buffer
   LD HL,(addr):INC HL:LD (addr),H      :\ Increment command line addressL
   CP 13:JR NZ,rdcmdlp                  :\ Loop until <cr>

PDP11

   \ If code has a Unix header, SP=>stack frame with parameters
   \ Otherwise, R1=>command line in local memory

ARM

   SWI "OS_GetEnv"                      :\ R0=>command line in local memory

BASIC

If the transient command is written in BASIC, the command line is already in local memory due to it being used by BASIC to local the program, and is collectable with the FNOS_GetEnv function in the ProgEnv program library.

Notes

Some filing systems provide the OSGBPB 9,0 call to copy the command line to local memory.

Jgharston 13:56, 2 December 2009 (UTC)