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, 26 insertions, 0 deletions

diff --git a/usr/df.c b/usr/df.c
new file mode 100644
index 0000000..ad1a000
--- /dev/null
+++ b/usr/df.c
@@ -0,0 +1,26 @@
+#include "stat.h"
+/* df: how much of the cart's battery-backed disk is left.
+ * 256-byte blocks, 128 of them (32 KiB), 32 inodes - small enough that the
+ * numbers are worth watching. */
+void main(void) {
+    unsigned char fs[4];
+    unsigned int used;
+    gfsstat(fs);
+    used = (unsigned int)(fs[0] - fs[1]);
+    puts("blocks  ");
+    putu(used);
+    putc('/');
+    putu(fs[0]);
+    puts(" used (");
+    putu((unsigned int)used * 256 / 1024);
+    puts("K of ");
+    putu((unsigned int)fs[0] * 256 / 1024);
+    puts("K)");
+    nl();
+    puts("inodes  ");
+    putu((unsigned int)(fs[2] - fs[3]));
+    putc('/');
+    putu(fs[2]);
+    puts(" used");
+    nl();
+}