usr: sort, cmp, strings, du, time

- sort [-r] [-n]: everything in RAM, which bounds it - a task has 8 KiB and a
  file caps at 3 KiB, so 96 lines of 2400 bytes with room for the stack.
  Insertion sort over an index; at that size the simple thing is fast and
  costs far less ROM. `uniq -c f | sort -n -r` finally works.
  NB the key needs a scratch SLOT of its own: gt() compares table entries, so
  reusing slot i as scratch overwrites the entries being shifted into it.
- cmp: reports the first differing byte, silent when the files match. There
  was no way to check a copy on the machine - you had to haul both to a host.
- strings [-n N]: pairs with xxd now that /bin/<prog> is readable. It finds
  "gbos sm83 (Game Boy Color)" inside /bin/uname.
- du [dir]: 256-byte blocks, the unit df and the filesystem use. Bytes
  overflow - /bin alone is 52 x 16 KiB, which wrapped a 16-bit counter and
  printed 32768. Recurses by re-opendir'ing, since the kernel keeps only one
  "directory being listed" cursor.
- time CMD: 1/64 s resolution from the tick counter. It rebuilds the child's
  command line at $A000 - which is its own argument area, so everything is
  copied to the stack first.

1 files changed, 60 insertions, 0 deletions

diff --git a/usr/strings.c b/usr/strings.c
new file mode 100644
index 0000000..b3db75d
--- /dev/null
+++ b/usr/strings.c
@@ -0,0 +1,60 @@
+#include "gbos.h"
+/* strings [-n N] [file]: print runs of N or more printable characters
+ * (default 4). Pairs with xxd now that /bin/<prog> is readable - it is how
+ * you find the text baked into a program image. */
+
+#define MAXRUN 64
+
+void main(void) {
+    char *argv[8];
+    char run[MAXRUN];
+    unsigned char argc = argv_parse(argv, 8);
+    char *nv = optval(argv, argc, 'n');
+    unsigned char min = nv ? atou(nv) : 4;
+    unsigned char len = 0, fd = NOFD, i;
+    char *fname = 0;
+    int ch;
+
+    if (min == 0) min = 4;
+    if (min > MAXRUN) min = MAXRUN;
+    for (i = 0; i < argc; i++) {
+        if (argv[i][0] == '-') continue;
+        if (nv == argv[i]) continue;
+        fname = argv[i];
+        break;
+    }
+    if (fname) {
+        fd = open(fname, O_READ);
+        if (fd == EISDIR) {
+            puts("strings: is a directory");
+            nl();
+            sexit(2);
+        }
+        if (fd == NOFD) {
+            puts("strings: no such file");
+            nl();
+            sexit(2);
+        }
+    }
+    for (;;) {
+        if (fd == NOFD) {
+            char c = readc();
+            ch = (c == EOF) ? -1 : c;
+        } else ch = fgetc(fd);
+        if (ch >= 32 && ch < 127) {
+            if (len < MAXRUN) run[len++] = (char)ch;
+            continue;
+        }
+        if (len >= min) {
+            writes(run, len);
+            nl();
+        } /* run ended: keep it? */
+        len = 0;
+        if (ch < 0) break;
+    }
+    if (len >= min) {
+        writes(run, len);
+        nl();
+    }
+    if (fd != NOFD) close(fd);
+}