usr: grep, more, cp, nc - and make pollcon pump the link

The shell has had pipes for a while with nothing to pipe *through*, and
an 18-row screen with no way to stop output scrolling off it.

- grep [-vin] PAT [file]: substring match (no regex), stdin or a file,
  grep(1)'s exit convention. The other end of the pipe, at last.
- more [file]: pages 17 lines at a time, --More-- bar in white-on-blue,
  any key pages, q quits. Counts *screen* rows, so wrapped lines pay
  their real cost. Keys come from pollin/pollcon, not stdin, so
  `cat big | more` still has a keyboard.
- cp SRC DST: the fs has rm/mkdir but no way to duplicate a file. mv is
  this plus rm (there is no rename). Rejects SRC == DST, which would
  otherwise truncate the source via O_WRITE before reading a byte.
- nc [-s] HOST PORT: raw TCP. Interactive (START sends the line with a
  CRLF, /q quits) or -s to pump stdin and print the reply with its own
  wall-clock idle timeout, because the kernel's blocking recv counts
  pumps, not seconds. Generalizes what chat/irc hardcode:
  `nc towel.blinkenlights.nl 23` works.

sys_pollcon now pumps the link before draining the console ring. The
ring is filled *by* net_pump, so a program that never touches the
network polled a ring nothing would ever fill: host-injected keys
(gbtype/gbdemo) hung `more` forever, and the Game Boy stopped answering
pings for as long as it ran. KGetc already pumps for this reason.

New tools take banks 35-38. Locals over statics in all four: a program's
_DATA starts at $A000, where the shell leaves the command line.

1 files changed, 83 insertions, 0 deletions

diff --git a/usr/more.c b/usr/more.c
new file mode 100644
index 0000000..6f6afa7
--- /dev/null
+++ b/usr/more.c
@@ -0,0 +1,83 @@
+#include "gbos.h"
+/* more [file]: page a file (or stdin) one screenful at a time.
+ *
+ * The terminal is 40x18, so anything longer than a screen scrolls off before
+ * you can read it (try `ls` on a full disk, or `cat` on a wget dump). This
+ * prints 17 lines, then paints a --More-- bar and waits for a keypress:
+ * SELECT opens the on-screen keyboard, any key pages forward, 'q' quits.
+ *
+ * Keys come from pollin()/pollcon(), NOT stdin - so `cat file | more` still
+ * has a keyboard even though its stdin is the pipe. (pollcon also means the
+ * host can drive it over the link with tools/gbtype.) */
+
+#define PAGE  17 /* TROWS - 1: leave a row for the bar */
+#define TCOLS 40
+
+static void sgr(unsigned char n) { /* emit ESC [ n m */
+    putc(27);
+    putc('[');
+    putu(n);
+    putc('m');
+}
+
+/* show the bar, block until a key arrives; 0 = the user asked to quit */
+static unsigned char waitkey(void) {
+    unsigned char c;
+    sgr(44);
+    sgr(37); /* white on blue */
+    puts("--More--");
+    sgr(0);
+    for (;;) {
+        c = pollin();          /* on-screen keyboard */
+        if (!c) c = pollcon(); /* link-injected console bytes */
+        if (c) break;
+        yield(); /* cooperative: let other procs run */
+    }
+    puts("\r        \r"); /* wipe the bar, stay on the same row */
+    return (c == 'q' || c == 'Q') ? 0 : 1;
+}
+
+void main(void) {
+    char *argv[4];
+    unsigned char argc = argv_parse(argv, 4);
+    unsigned char fd = NOFD, rows = 0, col = 0;
+    int ch;
+
+    if (argc > 0 && argv[0][0] != '-') {
+        fd = open(argv[0], O_READ);
+        if (fd == EISDIR) {
+            puts("more: is a directory");
+            nl();
+            sexit(2);
+        }
+        if (fd == NOFD) {
+            puts("more: no such file");
+            nl();
+            sexit(2);
+        }
+    }
+
+    for (;;) {
+        if (fd == NOFD) {
+            char c = readc();
+            ch = (c == EOF) ? -1 : c;
+        } else ch = fgetc(fd);
+        if (ch < 0) break;
+        putc((char)ch);
+
+        /* count screen rows, not input lines: a 100-char line wraps to three */
+        if (ch == '\n') {
+            rows++;
+            col = 0;
+        } else if (ch != '\r' && ++col == TCOLS) {
+            rows++;
+            col = 0;
+        }
+
+        if (rows >= PAGE) {
+            if (!waitkey()) break;
+            rows = 0;
+        }
+    }
+    if (fd != NOFD) close(fd);
+}