add ARGC, ARGV, and GETENV to access the command-line and environment variables

jumpforth.S

@@ -36,6 +36,11 @@
    .globl _start
 _start:
    cld
+   mov (%esp),%eax
+   mov %eax,data_ARGC
+   lea 4(%esp),%eax
+   mov %eax,data_ARGV
+   sub $64,%esp
    mov %esp,data_S0
    mov $return_stack_top,%ebp
    xor %ebx,%ebx
@@ -208,6 +213,8 @@ defconst __F_LENMASK,F_LENMASK,"F_LENMASK"
 /* NOTE: These are initialized in _start and read-only thereafter. */
 defvalue C0     /* first byte of the heap */
 defvalue S0     /* initial (empty) data stack pointer */
+defvalue ARGC   /* number of command-line arguments (including program name) */
+defvalue ARGV   /* address of array of command-line arguments (C string pointers) */
 
 /* STATE controls whether we are currently interpreting (0) or compiling (1) */
 defvar STATE,0  /* default to interpreting */

startup.4th

@@ -2240,8 +2240,31 @@ REVERT
 
 { LOCAL-LOOKUP ?DUP 0= IF DEFERS FIND-HOOK THEN } IS FIND-HOOK
 
+\ The environment consists of an array of pointers to "name=value" C strings
+\ immediately following the NULL-terminated array of argument pointers
+ARGV ARGC 1+ CELLS+ CONSTANT ENVIRON
+
 >> FORTH
 
+\ Convert a C string to a FORTH string by counting the characters
+: CSTRING  ( c-addr -- c-addr u )  0 BEGIN 2DUP + C@ WHILE 1+ REPEAT ;
+
+\ Return the string value of the named environment variable
+: GETENV  ( c-addr u -- c-addr2 u2 TRUE | FALSE )
+   2>R ENVIRON BEGIN
+      DUP @
+   DUP WHILE
+      0 BEGIN 2DUP + C@ DUP WHILE DUP [[ CHAR = ]] <> WHILE DROP 1+ REPEAT
+      IF 2DUP + 1+ CSTRING ELSE 0 0 THEN 2SWAP
+      2R@ COMPARE 0= IF 2RDROP ROT DROP TRUE EXIT THEN
+      2DROP CELL+
+   REPEAT ▪ NIP ▪ 2RDROP ;
+
+\ Return the string value of the numbered command-line argument
+\ Argument 0 is (normally) the pathname of the current program
+: ARGV  ( u -- c-addr u )
+   DUP ARGC U>= IF DROP 0 0 ELSE ARGV SWAP CELLS+ @ CSTRING THEN ;
+
 : LOCALS|  ( "<spaces?>name1…<spaces>namen<spaces>|" -- ; xn … x1 -- )   IMMEDIATE
    LOCAL-NAMES ▪ NULL TO LOCAL-NAMES
    0 BEGIN