DosGetEnv

#define INCL_DOSMISC

USHORT  rc = DosGetEnv(EnvSegment, CmdOffset);

PUSHORT          EnvSegment;    /* Selector (returned) */
PUSHORT          CmdOffset;     /* Command line offset (returned) */

USHORT           rc;            /* return code */

Example 

The following example shows how one may obtain information for program 
initialization.  The program locates the environment segment and prints 
the name of the command from the command line.  It then obtains the OS/2 
version number and prints it. 

#define INCL_DOS

#include <os2.h>

#define ENVVARNAME "PATH"

main()
{
  SEL       EnvSel;              /* Environment segment selector
                                     (returned) */
  USHORT    CmdOffset;           /* Offset into env. seg. of command line
                                     (returned) */
  PSZ FAR   *Commandline;        /* Pointer made by EnvSel and CmdOffset */
  USHORT    Version;             /* Version numbers (returned) */
  BYTE      MajorVer;            /* Major version number */
  BYTE      MinorVer;            /* Minor version number */
  USHORT    rc;                  /* return code */

  /** Locate environment segment and offset of command line. **/
  if(!(rc=DosGetEnv(&EnvSel,       /* Env. seg. selector (returned) */
                    &CmdOffset)))  /* Offset of command line
                                           (returned) */
    printf("Environment located; selector is %x offset is %x\n", EnvSel,
            CmdOffset);

  /** Use a macro to make a far pointer out of selector:offset pair.**/
  /** Notice the far-string pointer specification (%Fs) used to print **/

  Commandline = MAKEP(EnvSel, CmdOffset);
  printf("Command entered is %Fs.\n", Commandline);

  /** Obtain and print version info; use macros to extract info. **/
  /** We need to divide by 10 to obtain true version numbers.    **/

  if(!(rc=DosGetVersion(&Version)))
  {
    MajorVer = HIBYTE(Version) / 10;
    MinorVer = LOBYTE(Version) / 10;
    printf("This is OS/2 version %d.%d\n", MajorVer, MinorVer);
  }
}