use16
org 256

cld
lea di,[parameters]
lea si,[129]
movzx cx,[128]
rep movs byte [di],[si]
mov al,'$'
stos byte [di]

mov dx,parameters
mov ah,9
int 33

int 32

parameters db "",0
rb 1023

    

use16
org 256

cld
lea di,[parameters]
lea si,[129]
movzx cx,byte [128] ; <- You must specify the size
rep movs byte [di],[si]
mov al,'$'
stos byte [di]

mov dx,parameters
mov ah,9
int 33

int 32

parameters db "",0
rb 1023    

label cmd_line_size byte at 128
label cmd_line_text byte at 129    

use16
org 256
mov ax, cs
mov ds, ax
mov es, ax

mov dx, args
mov ax, 0x4810
int 47

mov ah, 9
int 33

mov ax, 76 * 256 + 0
int 33

args db 128, 127 dup ( ' ' ), 13, 10, '$'    

cld
lea di,[parameters]
lea si,[129]
movzx cx,byte [128] ; <- You must specify the size
rep movs byte [di],[si]
mov al,'$' ; <- Here $ is added at the end of the string for the function ah=9/int 33. You can simply change $ to 0 in al.
stos byte [di]    

replace_dollar_2_zero:
    mov al, '$'
    or cx, -1
    lea dx, [string]
    repne scas byte [di]
    jnz @f
    sub [es:di - 1], al
@@:
    retn    

        mov     cx, [_len]
        lea     si, [_cmd]
        lea     di, [_filename]
again:
        lodsb
        cmp     al, ' '
        jz      again
        stosb
        loop    again 
    

There seems to be conflicting documentation regarding int 2fh ax=4810h

My source is "The Programmers PC Sourcebook" by Thom Hogan from Microsoft Press dated 1991.

What is my book referring to if not the Command Line?

INT 2F - Multiplex - NOTES
        AH = identifier of program which is to handle the interrupt
           00h-3Fh reserved for IBM (for DOS)
           40h-7Fh reserved for Microsoft (for DOS)
           80h-B7h reserved for IBM
           B8h-BFh reserved for networks
           C0h-FFh reserved for applications
        AL is the function code
   This is a general mechanism for verifying the presence of a TSR and
   communicating with it.  When searching for a free identifier code for AH
   using the installation check (AL=00h), the calling program should set
   BX/CX/DX to 0000h and must not depend on any registers other than CS:IP
   and SS:SP to be valid on return, since numerous programs now use additional
   registers on input and/or output for the installation check.    

INT 2F - DOS 5+ DOSKEY, PCED v2.1 - READ INPUT LINE FROM CONSOLE
        AX = 4810h
        DS:DX -> line buffer (see #01344 at INT 21/AH=0Ah)
Return: AX = 0000h if successful
Notes:  the first byte (length) of the buffer MUST be 80h, or MS-DOS's DOSKEY
          chains to the previous handler; PCED and Novell DOS allow sizes
          other than 80h
        if the user's input is a macro name, no text is placed in the buffer
          even though AX=0000h on return; the program must immediately issue
          this call again to retrieve the expansion of the macro.  Similarly,
          if the user enters a special parameter such as $*, this call must
          be repeated to retrieve the expansion; on the second call, DOSKEY
          overwrites the macro name on the screen with its expansion.
        unlike DOSKEY, PCED expands all macros on the first call, so it is
          not necessary to make two calls; since the buffer is not empty on
          return, DOSKEY-aware programs will not make the second call
        DOSKEY chains if AL is not 00h or 10h on entry
        this function is supported by Novell DOS 7 DOSKEY
SeeAlso: AX=4800h,INT 21/AH=0Ah    

Format of Program Segment Prefix (PSP):
Offset  Size    Description     (Table 01378)
 00h  2 BYTEs   INT 20 instruction for CP/M CALL 0 program termination
                the CDh 20h here is often used as a signature for a valid PSP
 02h    WORD    segment of first byte beyond memory allocated to program
 04h    BYTE    (DOS) unused filler
                (OS/2) count of fake DOS version returns
 05h    BYTE    CP/M CALL 5 service request (FAR CALL to absolute 000C0h)
                BUG: (DOS 2+ DEBUG) PSPs created by DEBUG point at 000BEh
 06h    WORD    CP/M compatibility--size of first segment for .COM files
 08h  2 BYTEs   remainder of FAR JMP at 05h
 0Ah    DWORD   stored INT 22 termination address
 0Eh    DWORD   stored INT 23 control-Break handler address
 12h    DWORD   DOS 1.1+ stored INT 24 critical error handler address
 16h    WORD    segment of parent PSP    

 80h 128 BYTEs  commandline / default DTA
                command tail is BYTE for length of tail, N BYTEs for the tail,
                  followed by a BYTE containing 0Dh
Notes:
        for 4DOS and Windows95, the command tail may be more than 126
          characters; in that case, the length byte will be set to 7Fh (with
          an 0Dh in the  127th position at offset FFh), and the first 126
          characters will be stored in the PSP, with the entire command line
          in the environment variable CMDLINE; under at least some versions
          of 4DOS, the byte at offset FFh is *not* set to 0Dh, so there is no
          terminating carriage return in the PSP's command tail.
BUG:    When shelling out from the Borland Pascal 7.00 IDE, overly-long
          command lines will not be delimited by a 0Dh character, and the
          length byte is set to 80h!  A workaround is to always patch in a
          0Dh at the last position of the command line buffer before scanning
          the command line.