4-May-86 13:56:29-PDT,5916;000000000001
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Date: Sun, 4 May 86 15:49:46 cdt
From: Peter Wu <pwu@unix.macc.wisc.edu>
Message-Id: <8605042049.AA09143@unix.macc.wisc.edu>
To: info-ibmpc-request@mosis
Subject: input.c

/* INPUT version 1.0 by Peter Wu  5/86
** Send comments to
** uucp:   ..{ihnp4|seismo|ucbvax|harvard|allegra}!uwvax!uwmacc!pwu
** arpa:   uwmacc!pwu@uwvax.ARPA
**
** compile with IBMC using "cc input /ze"
** link with "clink input /stack:4000"
**
** Usage:
** Read a string from console into a DOS environment variable
** e.g. In a batch file:
**
**	echo off
**	input "Who are you? " name
**	if %name%.==God. goto greet
**	   .   \
**	   .	\-- (Note: %name% is an undocumented feature in Dos 3.1)
**	:greet
**	echo Your honor, why am I teleported here?
**
** This program relies on a number of undocumented features in DOS 3.1 to work
** properly. If you are not using DOS 3.1 on a real IBMPC, this program
** might not work. It's been tested with DOS 3.1 on IBM PC AT and IBM PC XT.
**
** See external document for more examples.
*/

#include <dos.h>
#include <stdio.h>
#include <string.h>
#include <ctype.h>
#include <conio.h>

#define VLEN 80
#define BUFLEN 1000

#define argprompt argv[1]
#define argname argv[2]

unsigned int _psp;
unsigned short peekw();
unsigned char peekb();
void pokeb();

main(argc,argv)
int argc;
char *argv[];
{
  unsigned short x, p, y, envsize, free;
  int found;
  char	c, var[VLEN+BUFSIZ+1], buf[BUFLEN];
  int i, varlen;

  if (argc != 3) {
    cputs("Usage: input <prompt> <variable name>\n\015");
    cputs("Input string will always be converted to lower case\n\015");
    cputs("E.g.  INPUT \"How are you? \" answer\n\015");
    cputs("      if %answer%.==fine. goto fine\n\015");
    exit(0);
  };

  varlen = strlen(argname);  /* var. name */
  if (varlen > VLEN) {
    cputs("Variable name too long\n");
    exit(1);
  };

  for (i=0; i <= varlen; i++) {  /* convert to upper case */
    var[i] = toupper(argname[i]);
  };

  strcat(var,"=");
  varlen++;

  p = _psp;

  do {	/* find DOS's segment */
    x = p;
    p = peekw(x,0xc);  /* terminate segment address */
  } while (p != x);

  if (peekb(x-1,0) != 0x4d) {
    cputs("Oops! Wrong DOS segment - something is wrong\n\015");
    exit(2);
  }

  /* found DOS segment at x */

  p = peekw(x-1,3) + x + 1;  /* DOS's env. space */
  envsize = peekw(p-1, 3) << 4;  /* size of env. space in bytes */

#ifdef DEBUG
  printf("Your env. size has total of %d bytes\n", envsize);
#endif


  /* The following code looks for an environment variable with the same
  ** name supplied by the user. If such a variable is found, it will be
  ** deleted (by copying the next variables over it)
  */
  x = 0;
  found = 0;
  do {	/* find environment var with the same name */

    if (mystrncmp(p,x,var,varlen) == 0) {  /* found same name */
      y = x;
      found = 1;
    };

    while (c=peekb(p,x)) {

#ifdef DEBUG
      putchar(c);
#endif
      if (found == 2) {
	pokeb(p,y,c);
	y++;
      };

      x++;
    };

    switch (found) {
      case 1: found=2; break;
      case 2: pokeb(p,y,c); y++; break;
    };

#ifdef DEBUG
    putchar('\n');
#endif

  } while (peekb(p,++x));

  if (found) {
    pokeb(p,y,'\0');
    x = y;
  };

  /* Ok. Now we have gotten rid of identical variable name. All that's
  ** left to be done is to make sure there's room to copy the new
  ** variable and input string into the environment space
  */

  /* now p:x points to the 0 at the end of current environment */

  /* calculate free env. space */
  free = envsize - x - 1;

#ifdef DEBUG
  printf("You have %d bytes left in your env.\n", free);
#endif

  cputs(argprompt);  /* prompt */
  buf[0] = BUFLEN - 3;
  cgets(buf);
  cputs("\n\015");  /* line feed on console after user entered string */

  /* now convert the input string to lower case */
  for (i=2; i < strlen(buf+2) + 2; i++) {  /* convert to lower case */
    buf[i] = tolower(buf[i]);
  };

  strcat(var,buf+2);  /* first two bytes of buf is not the string */

  /* check to see if things will fit */
  y = strlen(var);
  if (y+1 > free) {  /* Oops, won't fit! */
    cputs("Sorry, your environment space is full, program abort.\n\015");
    cputs("Try \"shell=c:\command.com /p /e:62\" in config.sys to\n\015");
    cputs("increase your environment space to 992 bytes\n\015");
    exit(3);
  };

  /* now copy the NAME=string to the end of environment space */
  for (i=0; i <= y; i++) {  /* poke the '\0' also, that's why I use <= */
    pokeb(p, x++, var[i]);
  };

  pokeb(p, x, 0);  /* terminate environment space */
}

/* strncmp with one string in a different segment */
mystrncmp(seg,offset,source,n)
short seg,offset;
int n;
char *source;
{
  int i, dif;

  for (i=0; i < n; i++) {
    dif = peekb(seg,offset+i) - source[i];
    if (dif) return dif;
  };
  return 0;
}

unsigned char peekb(seg,offset)
short seg,offset;
{
  char far *fptr;  /* far pointer (segment + offset) to character */
  /* if you forgot to use /ze option when you compile you'll get an
  ** error here about the '*'
  */

  FP_SEG(fptr) = seg;
  FP_OFF(fptr) = offset;
  return *fptr;
}

void pokeb(seg,offset,what)
short seg,offset;
char what;
{
  char far *fptr;  /* far pointer (segment + offset) to character */

  FP_SEG(fptr) = seg;
  FP_OFF(fptr) = offset;
  *fptr = what;
}

unsigned short peekw(seg,offset)
short seg,offset;
{
  unsigned far *fptr;  /* far pointer (segment + offset) to short */

  FP_SEG(fptr) = seg;
  FP_OFF(fptr) = offset;
  return *fptr;
}