Get/set switch char for PC/MS-DOS

[Tony Movshon]

The following program lets you check or set the DOS "switch" character.
This restores the ability (lost in DOS 3.x) to use the SWITCHAR option
in CONFIG.SYS. The default "switch" character is "/"; if any other
character is used instead (e.g. "-" a la Un*x), then "/" may be used
as a path-separator (again, a la Un*x). This is not an officially-
supported feature of DOS; some system programs and many application
programs may not act as if the switch character is changed. But if
you get bent out of shape by having to do running "\"-for-"/"
substitutions when you are running DOS, then this baby is for you.
It runs under any version of PC or MS-DOS between 2.00 and 3.10. It
may not work on later versions. Caveat emptor.

This is, of course, a shell archive; follow the instructions and
feed it to /bin/sh or unshar.

Tony Movshon
Psychology/NYU

uucp: {seismo|ihnp4|allegra}!cmcl2!xp!tony
arpa: xp!tony@nyu

#!/bin/sh
# This is a shell archive, meaning:
# 1. Remove everything above the #!/bin/sh line.
# 2. Save the resulting text in a file.
# 3. Execute the file with /bin/sh (not csh) to create the files:
# swchar.asm
# This archive created: Sat Mar 1 16:28:43 1986
export PATH; PATH=/bin:$PATH
if test -f 'swchar.asm'
then
echo shar: over-writing existing file "'swchar.asm'"
fi
cat << \SHAR_EOF > 'swchar.asm'
name swchar
page 55,132
title 'SWCHAR --- display or change switch character'
;
; Copyright 1984 by Michael D. Parker (mike@LOGICON)
; This program may be freely reproduced and modified for
; noncommercial use.
;
; ---------- Explanation

; This program that will either report or set the SWITCHAR from the DOS
; command level. Use for version of DOS 2.00 and LATER.

; Command line calling sequence
;
; swchar (to report current switchar)
;
; or
;
; swchar x (to change switchar to 'x')
;

; This program uses the SWITCHAR function of the DOS function request
; interrupt. This DOS function, 37H is listed by IBM as "used
; internally by DOS". It is passed either 1 or 2 parameters,
; depending on usage.

; To get the current SWITCHAR, put 37H in the AH register, 00H in the
; AL register, and generate an INT 21H. The current SWTICHAR will be
; returned in the DL register.

; To change the current SWITCHAR, put 37H in the AH register, 01H in
; the AL register, the new SWITCHAR in the DL register and generate an
; INT 21H.

; first the program equ statements

cr equ 0dh ;ASCII carriage return
lf equ 0ah ;ASCII line feed
eom equ '$' ;end of message flag
;Program Segment Prefix:
command equ 80h ;command line buffer
doscal equ 21h ;code for dos interrupt for processing
swread equ 3700h ;DOS call for reading switchar
swset equ 3701h ;DOS call for setting switchar
outstr equ 9h ;DOS call for output string

;
; CODE segment starts here
;
cseg segment para public 'CODE'
assume cs:cseg,ds:data,es:data,ss:stack
;
; first check to see if proper version of DOS to execute this item
; for
;
swchar proc far ;entry point from PC-DOS
push ds ;save DS:0000 for final
xor ax,ax ;return to PC-DOS
push ax
;
; now check for parameters on the command line
;
mov ax,data ;make our data segment addressable
mov es,ax ;via the ES register
mov si,offset command
lodsb ;check string length byte,
or al,al ;any char present?
jz swc200 ;no,then get current switchar
;
; examine command line, and stop if non-blank character found
; or end of line (cr)
;
swc150: ;scan for start of char
lodsb ;get next char
cmp al,cr ;if carriage return,char is missing
je swc200 ;so jump to get current switchar
cmp al,' ' ;if blank, keep looking
je swc150
;
; a new character for the switchar
;
mov es:chrx,al ;save the character
mov ax,es ;now set DS=ES for remainder of program
mov ds,ax
mov dl,ds:chrx ;get the character for new switchar
mov ax,swset ; change the SWITCHAR
int doscal ;perform DOS call
jmp swc250 ;tell the abuser what the char is now
;
; find the current switchar and print it out
;
;let ES:DI = addr of name field
swc200:
mov ax,es ;now set DS=ES for remainder
mov ds,ax ;of the program.
swc250:
mov ax,swread ; (yes)-read SWITCHAR
int doscal ;call DOS to read switchar
mov byte ptr curch,dl ; prepare report string
mov ah,outstr ; print report string
mov dx,offset report
int doscal ;make DOS call
ret ;all done-- then return to DOS
swchar endp

cseg ends
;
; DATA segment starts here
;

data segment para public 'DATA'

report db 'SWITCHAR is ' ;Tell the user what current char is
curch db 'X' ;space for current switchar
db cr,lf,eom ;message terminator

chrx db 0 ;temp storage

data ends

;
; STACK Segment starts here
;
stack segment para stack 'STACK'
db 64 dup (?) ;just something to keep things buzy
stack ends
end swchar

SHAR_EOF
if test 3458 -ne "`wc -c 'swchar.asm'`"
then
echo shar: error transmitting "'swchar.asm'" '(should have been 3458 characters)'
fi
# End of shell archive
exit 0