usr: ls -l, df, mv, tail, tee, sleep, help, poweroff

Filling in the core utilities the box was missing:

- ls -l: type, links and size, now that stat() exists. The screen is 40
  columns, so it is "d  1   256 name", not the GNU sprawl. Sizes were
  previously unknowable except one file at a time with wc -c.
- df: blocks and inodes, used and free, on the 32 KiB cart disk.
- mv: no rename syscall, so it is cp + rm - and the copy has to finish before
  the source goes, or a failure loses the file.
- tail [-n N]: no seek syscall, so it streams the input through a ring of N
  lines rather than jumping to the end. N is capped by that ring.
- tee: the missing half of a pipeline - `cat big | tee copy | wc -l`.
- sleep: the thing every script needs; the kernel counts 1/64 s ticks.
- help: lists every command the shell knows, walked out of the kernel's own
  name table. The box previously had no way to tell you what it could do.
- poweroff: the only safe way to stop a gbos that has data on it. The cart's
  battery RAM is written when the emulator exits cleanly, so killing it loses
  the whole filesystem - it comes back "formatted". Found while testing /rc.

1 files changed, 25 insertions, 0 deletions

diff --git a/usr/help.c b/usr/help.c
new file mode 100644
index 0000000..5a68d57
--- /dev/null
+++ b/usr/help.c
@@ -0,0 +1,25 @@
+#include "gbos.h"
+/* help: list every command the shell knows. The kernel owns the name table
+ * (sys_lookup searches it), so walk program ids and ask for each one's name -
+ * the box had no way to discover what it can do. */
+void main(void) {
+    char name[16];
+    unsigned char id, col = 0;
+    for (id = 0; id < 64; id++) {
+        name[0] = 0;
+        progname(id, name);
+        name[15] = 0;
+        if (!name[0]) continue;
+        if (lookup(name) == NOFD) continue; /* not reachable from the shell */
+        puts(name);
+        col = (unsigned char)(col + 1);
+        if (col == 4) {
+            nl();
+            col = 0;
+        } else {
+            unsigned char k = strlen(name);
+            while (k++ < 10) putc(' ');
+        }
+    }
+    if (col) nl();
+}