Subversion Repositories SvarDOS

; offset within EXECPROG for out and in filenames in case stdin or stdout

; needs to be redirected (0xffff=no redirection)

REDIR_OUTFIL dw 0xffff    ; +EBh

REDIR_INFIL dw 0xffff     ; +EDh

REDIR_OUTAPPEND dw 0      ; +EFh

; revert stdin/stdout redirections (if any) to their initial state

call REVERT_REDIR_IF_ANY

; redirect stdout if required

call REDIR_OUTFILE_IF_REQUIRED

; variables used to revert stdin/stdout to their initial state

OLD_STDOUT dw 0xffff

OLD_STDIN  dw 0xffff

; *** ROUTINES ***************************************************************

; revert stdin/stdout redirections (if any) to their initial state

; all memory accesses are CS-prefixes because this code may be called at

; times when DS is out of whack.

REVERT_REDIR_IF_ANY:

; is stdout redirected?

mov bx, [OLD_STDOUT]

cmp bx, 0xffff

je STDOUT_DONE

; revert the stdout handle (dst in BX alread)

mov cx, 1        ; src handle (1=stdout)

mov ah, 0x46     ; redirect a handle

int 0x21

mov [OLD_STDOUT], word 0xffff ; mark stdout as "not redirected"

STDOUT_DONE:

ret

; redirect stdout if REDIR_OUTFIL points to something

REDIR_OUTFILE_IF_REQUIRED:

mov si, [REDIR_OUTFIL]

cmp si, 0xffff

je NO_STDOUT_REDIR

add si, EXECPROG       ; si=output file

mov ax, 0x6c00         ; Extended Open/Create

mov bx, 1              ; access mode (0=read, 1=write, 2=r+w)

xor cx, cx             ; file attribs when(if) file is created (0=normal)

mov dx, [REDIR_OUTAPPEND] ; action if file exist (0x11=open, 0x12=truncate)

int 0x21               ; ax=handle on success (CF clear)

mov [REDIR_OUTFIL], word 0xffff

jc NO_STDOUT_REDIR     ; TODO: abort with an error message instead

; duplicate current stdout so I can revert it later

push ax                ; save my file handle in stack

mov ah, 0x45           ; duplicate file handle BX

mov bx, 1              ; 1=stdout

int 0x21               ; ax=new (duplicated) file handle

mov [OLD_STDOUT], ax   ; save the old handle in memory

; redirect stdout to my file

pop bx                 ; dst handle

mov cx, 1              ; src handle (1=stdout)

mov ah, 0x46           ; "redirect a handle"

int 0x21

; close the original file handle, I no longer need it

mov ah, 0x3e           ; close a file handle (handle in BX)

NO_STDOUT_REDIR:

ret