implement @SYSTEM function

This allows you to collect the output of commands in cells. Previously
This had to be done with a macro, but it's very convenient to write
@value(@System("query value")).

atfuncs/Makefile

@@ -7,7 +7,7 @@ LDLIBS=
 
 all: atfuncs.a
 
-atfuncs.a: date.o weekday.o product.o atfuncs.o
+atfuncs.a: date.o weekday.o product.o atfuncs.o system.o
 	$(AR) r $@ $^
 
 clean:

atfuncs/atfuncs.c

@@ -12,7 +12,9 @@ void init_at_funcs()
     // Setup any @functions here.
     functions[AT_WEEKDAY] = (atfunc_t) at_weekday;
     functions[AT_PRODUCT] = (atfunc_t) at_product;
+    functions[AT_SYSTEM] = (atfunc_t) at_system;
 
     // You can pass 1 or more parameters to @PRODUCT().
     fn_numargs[AT_PRODUCT] = AT_ARGS_VARIABLE | 1;
+    fn_numargs[AT_SYSTEM] = 1;
 }

atfuncs/atfuncs.h

@@ -16,17 +16,22 @@ extern int16_t encode_date(int16_t *datenums);
 
 extern int16_t check_three_numbers();
 extern int16_t check_one_number();
+extern int16_t check_one_string();
 extern int16_t get_integer();
 extern int16_t push_integer(uint16_t val);
 extern int16_t push_one();
 extern int16_t push_zero();
+extern int16_t drop_one_push_err();
+extern int16_t drop_one_push_stack_string(char *str);
+extern char * peek_string(int16_t n);
 extern void mod_real_d();
 extern void int_real_d();
 extern void drop_one();
 extern void swap_TOS();
 
-// @PRODUCT replaced the previously unimplemented @CALL
+// Replaced previously unimplemented functions
 #define AT_CALL AT_PRODUCT
+#define AT_TERM2 AT_SYSTEM
 
 enum {
     AT_NA,
@@ -162,7 +167,7 @@ enum {
     AT_PMT2,
     AT_PV2,
     AT_FV2,
-    AT_TERM2,
+    AT_SYSTEM,
     AT_NUM_FUNCS,
 };
 
@@ -173,6 +178,7 @@ extern int8_t fn_numargs[AT_NUM_FUNCS];
 
 int16_t at_date();
 int16_t at_weekday();
+int16_t at_system();
 int16_t at_product(int16_t cnt);
 
 void init_at_funcs();

atfuncs/system.c

@@ -0,0 +1,37 @@
+#include <stdint.h>
+#include <stdlib.h>
+#include <stdio.h>
+#include <stdbool.h>
+#include <stddef.h>
+
+#include "lottypes.h"
+#include "lotfuncs.h"
+#include "lotdefs.h"
+#include "atfuncs.h"
+
+int16_t at_system()
+{
+    FILE *cmd;
+    char buf[512] = {0};
+
+    if (!check_one_string()) {
+        return 0;
+    }
+
+    cmd = popen(peek_string(0), "r");
+
+    if (cmd == NULL) {
+        return drop_one_push_err();
+    }
+
+    // We can read at most 512 bytes of output.
+    fscanf(cmd, "%511[^\n]", buf);
+
+    // We return @ERR if the command returned failure.
+    if (pclose(cmd) != EXIT_SUCCESS) {
+        return drop_one_push_err();
+    }
+
+    // Return the output as a string.
+    return drop_one_push_stack_string(buf);
+}

globalize.lst

@@ -83,3 +83,5 @@ display_filename
 filename_length
 mac_nobreak
 mac_str
+drop_one_push_stack_string
+drop_one_push_err

res/l123txt3.txt

@@ -2767,7 +2767,7 @@
 130 "PMT2"
 131 "PV2"
 132 "FV2"
-133 "TERM2"
+133 "SYSTEM"
 134 "?"
 
 =group 21, 256 bytes

test/runtests.sh

@@ -704,6 +704,10 @@ function check_calculations()
     verify_result_contents '@UPPER("hello")' "HELLO"
     verify_result_contents '@WEEKDAY(@DATE(2001,12,25))' "3"
     verify_result_contents '@PRODUCT(1,2,3)' "6"
+    verify_result_contents '@ISERR(@SYSTEM("false"))' "1"
+    verify_result_contents '@ISERR(@SYSTEM("true"))' "0"
+    verify_result_contents '@SYSTEM("printf XyZzY")' "XyZzY"
+    verify_result_contents '@VALUE(@SYSTEM("echo 32+6 | bc"))' "38"
 }
 
 function check_crash_bugs()