Only in fasm/source: fasm.diff
diff -ur fasm/source/Linux/fasm.asm fasmn/source/Linux/fasm.asm
--- fasm/source/Linux/fasm.asm	2007-02-18 11:46:20.000000000 +0200
+++ fasmn/source/Linux/fasm.asm	2007-02-28 13:21:27.000000000 +0200
@@ -13,7 +13,11 @@
 	call	display_string
 
 	mov	[command_line],esp
+	mov	eax, [esp+8]
+	sub	eax, 2
+	mov	[param_ptr], eax 
 	pop	eax
+	mov	[param_count], eax
 	lea	esp,[esp+eax*4]
 	pop	eax
 	pop	[environment]
@@ -137,9 +141,26 @@
 	je	passes_option
 	cmp	al,'P'
 	je	passes_option
+	cmp	al,'d'
+	je	define_option
+	cmp	al,'D'
+	je	define_option
       bad_params:
 	stc
 	ret
+      define_option:
+	mov	eax, esi
+@@:	cmp	[esi], word ':='
+	je	@f
+	cmp	[esi], byte 0
+	je	bad_params
+	inc	esi
+	jmp	@b
+@@:	xor	eax, esi
+	jz	bad_params	
+	cmp	[esi+2], byte 0
+	jne	next_param
+	jmp	bad_params
       memory_option:
 	cmp	byte [esi],0
 	jne	get_memory_setting
@@ -217,6 +238,7 @@
        db 'optional settings:',0xA
        db ' -m <limit>  set the limit in kilobytes for the memory available to assembler',0xA
        db ' -p <limit>  set the maximum allowed number of passes',0xA
+       db ' -dSYMBOL:=VALUE  define a symbolic constant',0xA
        db 0
 _memory_prefix db '  (',0
 _memory_suffix db ' kilobytes memory)',0xA,0
diff -ur fasm/source/preproce.inc fasmn/source/preproce.inc
--- fasm/source/preproce.inc	2007-02-18 11:46:20.000000000 +0200
+++ fasmn/source/preproce.inc	2007-02-28 13:24:59.000000000 +0200
@@ -47,6 +47,45 @@
 	mov	edx,esi
 	call	open
 	jc	main_file_not_found
+	push	esi
+	push	ebx
+	mov	esi, [param_ptr]
+do_param:
+	mov	edi, esi
+	cmp	[esi], word '-d'
+	je	@f
+	cmp	[esi], word '-D'
+	jne	not_symdef
+@@:	xor	ecx, ecx
+	add	esi, 2
+@@:	inc	ecx
+	cmp	[esi+ecx], byte ':'
+	jne	@b
+	add	edi, 2
+	add	edi, ecx
+	mov	ch, 10b
+	call	add_preprocessor_symbol
+	xor	ecx, ecx
+@@:	inc	ecx
+	cmp	[edi+ecx], byte 0
+	jne	@b
+	mov	[edi], byte 0x1a
+	mov	[edx+8], edi						
+	mov	[edx+12], ecx
+	sub	ecx, 2
+	mov	[edi+1], cl
+not_symdef:
+	dec	[param_count]
+	jz	done_params
+@@: 	inc	edi
+	cmp	[edi], byte 0
+	jne	@b
+	mov	esi, edi
+	inc	esi
+	jmp	do_param
+done_params:
+	pop	ebx
+	pop	esi
 	mov	edi,[memory_start]
 	call	preprocess_file
 	mov	eax,[error_line]
diff -ur fasm/source/variable.inc fasmn/source/variable.inc
--- fasm/source/variable.inc	2007-02-18 11:46:20.000000000 +0200
+++ fasmn/source/variable.inc	2007-02-28 13:18:24.000000000 +0200
@@ -121,3 +121,6 @@
 
 characters rb 100h
 converted rb 100h
+
+param_count	rd 1
+param_ptr	rd 1