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, 51 insertions, 0 deletions

diff --git a/usr/mv.c b/usr/mv.c
new file mode 100644
index 0000000..76d9e62
--- /dev/null
+++ b/usr/mv.c
@@ -0,0 +1,51 @@
+#include "gbos.h"
+/* mv SRC DST: there is no rename syscall, so this is cp + rm. The copy has to
+ * succeed before the source is removed - a half-copied DST plus a deleted SRC
+ * loses the file. */
+
+static unsigned char streq(const char *a, const char *b) {
+    while (*a && *a == *b) {
+        a++;
+        b++;
+    }
+    return (unsigned char)(*a == *b);
+}
+
+void main(void) {
+    char *argv[4];
+    unsigned char argc = argv_parse(argv, 4);
+    unsigned char in, out;
+    int ch;
+
+    if (argc < 2) {
+        puts("usage: mv SRC DST");
+        nl();
+        sexit(2);
+    }
+    if (streq(argv[0], argv[1])) sexit(0); /* nothing to do */
+
+    in = open(argv[0], O_READ);
+    if (in == EISDIR) {
+        puts("mv: SRC is a directory");
+        nl();
+        sexit(2);
+    }
+    if (in == NOFD) {
+        puts("mv: no such file: ");
+        puts(argv[0]);
+        nl();
+        sexit(2);
+    }
+    out = open(argv[1], O_WRITE);
+    if (out > 3) {
+        puts("mv: cannot create ");
+        puts(argv[1]);
+        nl();
+        close(in);
+        sexit(2);
+    }
+    while ((ch = fgetc(in)) >= 0) fputc(out, (char)ch);
+    close(in);
+    close(out);
+    fremove(argv[0]); /* only now is it safe */
+}