From d18964c5fe9d745eeb9b88b003f01c43dadcf018 Mon Sep 17 00:00:00 2001
From: Kamil Kaminski <kyle@kkaminsk.com>
Date: Mon, 6 Feb 2012 04:52:13 -0600
Subject: forgot a duped fd, add another pipe sample

---
 Makefile          |  5 ++--
 dup.c             |  8 +++++--
 parent_to_child.c | 71 +++++++++++++++++++++++++++++++++++++++++++++++++++++++
 3 files changed, 80 insertions(+), 4 deletions(-)
 create mode 100644 parent_to_child.c

diff --git a/Makefile b/Makefile
index 2e1d8c1..e6adbe2 100644
--- a/Makefile
+++ b/Makefile
@@ -1,6 +1,7 @@
 BINS = ascii class depipe_strings dup fpipe pipe realloc strpbrk strsep \
        tokenizer getopt prime_mask linked_list pi_bbp string_tokenizer  \
-       tcpserver tcpclient regexp c99 asm playground_05-25-2011
+       tcpserver tcpclient regexp c99 asm playground_05-25-2011 \
+       parent_to_child
 
 CURL = curl_tomem curl_tofile
 
@@ -25,4 +26,4 @@ $(CURL): %: %.c
 .PHONY: clean
 
 clean:
-	rm -f ./$(BINS) ./$(CURL)
+	@rm -f ./$(BINS) ./$(CURL)
diff --git a/dup.c b/dup.c
index 7112628..1d4bc02 100644
--- a/dup.c
+++ b/dup.c
@@ -31,8 +31,10 @@ int main(int argc, char **argv)
 
         if (!pid)
         {
-            close(1);         /* break the link to stdout */
+            close(1);         /* break the link to stdout, dup2 already kills this but meh */
             dup2(pfds[1], 1); /* redirect stdout to pfds[1] */
+            close(pfds[1]);   /* new stdout has been setup above, pfds[1] can be closed since it's a dup */
+
             close(pfds[0]);   /* child will not be reading anything from out pipe */
 
             execlp("ls", "ls", "-1", NULL);
@@ -40,7 +42,9 @@ int main(int argc, char **argv)
         else
         {
             close(0);         /* break the link to stdin */
-            dup2(pfds[0], 0); /* redirect stdout to pfds[0] */
+            dup2(pfds[0], 0); /* redirect stdin to pfds[0] */
+            close(pfds[0]);   /* new stdin has been setup above, pfds[1] can be closed since it's a dup */
+
             close(pfds[1]);   /* parent will not be writing anything into our pipe */
 
             ret = waitpid(pid, &stat_loc, WCONTINUED);
diff --git a/parent_to_child.c b/parent_to_child.c
new file mode 100644
index 0000000..c0c0695
--- /dev/null
+++ b/parent_to_child.c
@@ -0,0 +1,71 @@
+/* dup.c
+ *
+ * Parent piping to a child where child spawns using new stdin
+ *
+ */
+
+#include <stdio.h>
+#include <stdlib.h>
+#include <unistd.h>
+#include <string.h>
+#include <wait.h>
+
+extern char **environ;
+
+int main(int argc, char **argv)
+{
+    pid_t pid;
+    int stat_loc;
+
+    char *str = "all base are belong to us";
+    int pfds[2];
+    int ret;
+
+    if (pipe(pfds) == 0)
+    {
+        pid = fork();
+        if (pid == -1)
+        {
+            perror("fork");
+            exit(EXIT_FAILURE);
+        }
+
+        if (pid) /* parent */
+        {
+            close(1);         /* break the link to stdout, dup2 already kills this but meh */
+            dup2(pfds[1], 1); /* redirect stdout to pfds[1] */
+            close(pfds[1]);   /* new stdout has been setup above, pfds[1] can be closed */
+            close(pfds[0]);   /* parent will not be reading anything from out pipe */
+
+            printf("parent sends out: \"%s\"\n", str);
+            fflush(stdout);   /* printf is buffered! */
+            close(1);         /* close stdin or else the child would not know that he's done reading */
+
+            ret = waitpid(pid, &stat_loc, WCONTINUED);
+        }
+        else /* child */
+        {
+            close(0);         /* break the link to stdin */
+            dup2(pfds[0], 0); /* redirect stdin to pfds[0] */
+            close(pfds[0]);   /* new stdin has been setup above, pfds[1] can be closed */
+            close(pfds[1]);   /* parent will not be writing anything into our pipe */
+
+            /* here the child will use a redefined stdin */
+            execlp("wc", "wc", NULL);
+            /* if there wasn't a spawn then we would need to close stdin */
+        }
+    }
+    else
+    {
+        perror("pipe");
+        exit(EXIT_FAILURE);
+    }
+
+    ret = ret; /* hush the dumb compiler */
+
+    close(pfds[0]);
+    close(pfds[1]);
+
+    return 0;
+}
+
-- 
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