1 files changed, 99 insertions, 0 deletions
diff --git a/c/sh.c b/c/sh.c
new file mode 100644
index 0000000..c24ed9f
--- /dev/null
+++ b/c/sh.c
@@ -0,0 +1,99 @@
+#include "gbos.h"
+/* gbos shell: prompt -> read a line -> parse -> run, with I/O redirection
+   ( > file, < file ) and pipes ( cmd1 | cmd2, via a temp file ).
+   Operators must be space-separated (e.g.  cat readme > out ). */
+
+#define ARGV0 ((char *)0xA000)   /* where a child reads its command line */
+
+/* split s into space-separated tokens (NUL-terminated in place). */
+static unsigned char tokenize(char *s, char **tok, unsigned char max) {
+    unsigned char n = 0;
+    for (;;) {
+        while (*s == ' ') *s++ = 0;
+        if (*s == 0) break;
+        if (n < max) tok[n++] = s;
+        while (*s && *s != ' ') s++;
+    }
+    return n;
+}
+
+static unsigned char isop(char *t, char c) { return t[0] == c && t[1] == 0; }
+
+/* build the child command line "name\0arg1 arg2\0" at 0xA000 */
+static void set_cmdline(char **tok, unsigned char start, unsigned char end) {
+    char *p = ARGV0, *t;
+    unsigned char i;
+    t = tok[start];
+    while (*t) *p++ = *t++;
+    *p++ = 0;                        /* NUL after the command word */
+    for (i = start + 1; i < end; i++) {
+        if (i > start + 1) *p++ = ' ';
+        t = tok[i];
+        while (*t) *p++ = *t++;
+    }
+    *p = 0;
+}
+
+/* run tok[start..end): parse its own >/< redirects, honor forced in/out. */
+static void run(char **tok, unsigned char start, unsigned char end,
+                unsigned char infd, unsigned char outfd) {
+    unsigned char i, cmdend = end, myin = NOFD, myout = NOFD, id, pid;
+    for (i = start; i < end; i++) {
+        if (isop(tok[i], '>')) {
+            if (i + 1 < end) myout = open(tok[i + 1], O_WRITE);
+            if (i < cmdend) cmdend = i;
+        } else if (isop(tok[i], '<')) {
+            if (i + 1 < end) myin = open(tok[i + 1], O_READ);
+            if (i < cmdend) cmdend = i;
+        }
+    }
+    id = lookup(tok[start]);
+    if (id == NOFD) { puts(tok[start]); puts(": not found"); nl(); goto done; }
+    set_cmdline(tok, start, cmdend);
+    pid = fork();
+    if (pid == 0) {
+        if (myin != NOFD) setin(myin);
+        else if (infd != NOFD) setin(infd);
+        if (myout != NOFD) setout(myout);
+        else if (outfd != NOFD) setout(outfd);
+        exec(id);
+    }
+    wait();
+done:
+    if (myin != NOFD) close(myin);
+    if (myout != NOFD) close(myout);
+}
+
+void main(void) {
+    char line[80];
+    char *tok[16];
+    for (;;) {
+        unsigned char nt, i, pipepos, c;
+        puts("$ ");
+        /* read a line (echoing), stop at newline; exit on EOF */
+        i = 0;
+        for (;;) {
+            c = readc();
+            if (c == EOF) return;
+            if (c == '\r' || c == '\n') { nl(); break; }
+            if (i < 79) { line[i++] = c; putc(c); }
+        }
+        line[i] = 0;
+        nt = tokenize(line, tok, 16);
+        if (nt == 0) continue;
+        pipepos = 0;
+        for (i = 1; i < nt; i++)
+            if (isop(tok[i], '|')) { pipepos = i; break; }
+        if (pipepos) {
+            unsigned char pw = open("__pipe", O_WRITE);
+            run(tok, 0, pipepos, NOFD, pw);
+            close(pw);
+            { unsigned char pr = open("__pipe", O_READ);
+              run(tok, pipepos + 1, nt, pr, NOFD);
+              close(pr); }
+            fremove("__pipe");
+        } else {
+            run(tok, 0, nt, NOFD, NOFD);
+        }
+    }
+}