feat: introduce streq and printErr

user/pipesrc.c

@@ -0,0 +1,43 @@
+#include "ulib.h"
+
+/*
+ * Left half of shell.c's new `cmd1 | cmd2` pipeline syntax's live demo.
+ * jobctlSpawnPiped (jobctl.h) bakes a real pipe end into this process's own
+ * fd 1 BEFORE it ever runs a single instruction (vfsPipeAttachInto, vfs.h)
+ * -- from this program's own point of view it writes its stdout exactly
+ * like any well-behaved Unix filter, with no idea a pipe is on the other
+ * end instead of the real console. fd 2 (stderr) is deliberately left
+ * alone by the pipeline setup (only fd 0/fd 1 are ever redirected, matching
+ * a real shell), so the diagnostic lines below go straight to the real
+ * console even though fd 1's own payload does not -- writing them through
+ * fd 1 instead (print()/printDec(), ulib.h, both hardcoded to fd 1) would
+ * corrupt the exact payload pipesink.c compares against.
+ *
+ * Deliberately writes once and exits immediately: pipesink.c's own
+ * blocking read has to notice the resulting EOF (this process's own exit
+ * reclaims its fd 1, dropping the pipe's writer count to 0 -- see
+ * sched.c's reclaimOpenFds) the same way every other pipe/fifo EOF demo in
+ * this kernel already does, not just receive the payload.
+ */
+
+#define pipelinePayload "pipeline-payload-ok"
+
+static void printErr(const char* text)
+{
+    userWrite(2, text, stringLength(text));
+}
+
+int main(void)
+{
+    printErr("pipesrc: writing payload to stdout (pipe)\n");
+
+    unsigned long length = stringLength(pipelinePayload);
+    long written = userWrite(1, pipelinePayload, length);
+    if (written != (long)length) {
+        printErr("pipesrc: FAIL short/failed write\n");
+        return 1;
+    }
+
+    printErr("pipesrc: wrote payload\n");
+    return 0;
+}