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, 16 insertions, 0 deletions

diff --git a/usr/sleep.c b/usr/sleep.c
new file mode 100644
index 0000000..3c229df
--- /dev/null
+++ b/usr/sleep.c
@@ -0,0 +1,16 @@
+#include "gbos.h"
+/* sleep N: wait N seconds (the kernel counts 1/64 s ticks, so N is capped at
+ * what fits: 3 seconds per gsleep call, looped). Mostly useful in scripts and
+ * to pace a background job. */
+void main(void) {
+    char *argv[4];
+    unsigned char argc = argv_parse(argv, 4);
+    unsigned char n, i;
+    if (argc < 1) {
+        puts("usage: sleep SECONDS");
+        nl();
+        sexit(2);
+    }
+    n = atou(argv[0]);
+    for (i = 0; i < n; i++) gsleep(64); /* 64 ticks = one second */
+}