Mine

#include <dos.h>
#include <errno.h>
#include <string.h>
#include <stdlib.h>

struct __execblock {
    unsigned short  envseg;
    void far *      cmdtail;
    void far *      fcb1;
    void far *      fcb2;
};

int __dodexec( const char *path, struct __execblock *xb );
#pragma aux __dodexec = \
    "mov ax, 0x4B00"    \
    "int 0x21"          \
    "jnc finish"        \
    "mov _doserrno, ax" \
    "mov ax, 0xFFFF"    \
    "finish:"           \
    parm [dx] [bx]      \
    value [ax]          \
    modify [ax bx dx];

unsigned char __dogetrt( void );
#pragma aux __dogetrt = \
    "mov ah, 0x4D"      \
    "int 0x21"          \
    value [al]          \
    modify [ax];

int _exec( const char *path, const char *cmdline )
{
    char fullcmdline[ 128 ];
#if 1
    char far *envp;
    int i, size = 0;
    unsigned j = 0, seg;
#endif
    struct __execblock xb = { 0, NULL, NULL, NULL };

#if 1
    for( i = 0; environ[ i ]; i++, size += 2 ) {
        int j;

        while( environ[ i ][ j ] ) j++;
        size += j;
    }
    size += 2;

    allocmem( size / 16 + 1, &seg );
    envp = MK_FP( seg, 0 );

    for( i = 0, j = 0; environ[ i ]; i++, j = 0 ) {
        while( environ[ i ][ j ] ) {
            *envp++ = environ[ i ][ j++ ];
        }

    }
    _dos_write( 1, MK_FP( seg, 0 ), size, &j );
    *envp = '\0';

    xb.envseg = seg;
#endif
    xb.cmdtail = fullcmdline;
    
    fullcmdline[ 0 ] = strlen( cmdline );
    fullcmdline[ fullcmdline[ 0 ] ] = '\r';
    strcpy( &fullcmdline[ 1 ], cmdline );

    if( __dodexec( path, &xb ) < 0 ) return( -1 );

    return( __dogetrt() );
}