Add a naive /bin/fgrep for testing pipes.

Userland/fgrep.cpp

@@ -0,0 +1,20 @@
+#include <stdio.h>
+#include <string.h>
+#include <unistd.h>
+
+int main(int argc, char** argv)
+{
+    if (argc < 2) {
+        printf("usage: fgrep <str>\n");
+        return 0;
+    }
+    for (;;) {
+        char buf[4096];
+        fgets(buf, sizeof(buf), stdin);
+        if (feof(stdin))
+            return 0;
+        if (strstr(buf, argv[1]))
+            write(1, buf, strlen(buf));
+    }
+    return 0;
+}