From 65966ded0cc15c5966c6568cf0ff2f2bbe1fc29a Mon Sep 17 00:00:00 2001
From: Stefan Zabka <zabkaste@hu-berlin.de>
Date: Sun, 24 May 2020 12:09:46 +0200
Subject: Big remodelling

---
 shell/beispiele/dup/dup.c | 51 +++++++++++++++++++++++++++++++++++++++++++++++
 1 file changed, 51 insertions(+)
 create mode 100644 shell/beispiele/dup/dup.c

(limited to 'shell/beispiele/dup/dup.c')

diff --git a/shell/beispiele/dup/dup.c b/shell/beispiele/dup/dup.c
new file mode 100644
index 0000000..ea3c5a6
--- /dev/null
+++ b/shell/beispiele/dup/dup.c
@@ -0,0 +1,51 @@
+#include <stdio.h>
+#include <stdlib.h>
+#include <unistd.h>
+
+/* https://www.youtube.com/watch?v=gaXigSu72A4 */
+static inline void die(const char* msg) {
+	perror(msg);
+	exit(EXIT_FAILURE);
+}
+
+int main(int argc, char **argv) {
+	int pdes[2];
+	pid_t child;
+ 	
+	if (pipe(pdes) < 0)
+		die("pipe()");
+ 	
+	if ((child = fork()) < 0)
+		die("fork()");
+ 	
+	if (child == 0) {
+		/* child process */
+      	close(pdes[0]);
+		close(1);       /* close stdout */
+		
+		if (dup(pdes[1]) < 0)
+			die("dup()");
+		
+		/* now stdout and pdes[1] are equivalent (dup returns lowest free descriptor) */
+		if (execlp("cat", "cat", "/etc/passwd", NULL) < 0)
+			die("execlp()");
+		
+		exit(EXIT_SUCCESS);
+	}
+	else {
+		/* parent process */
+		close(0);       /* close stdin */
+		close(pdes[1]);
+		
+		if (dup(pdes[0]) < 0)
+			die("dup()");
+		
+		/* now stdin and pdes[0] are equivalent (dup returns lowest free descriptor) */
+		if (execlp("wc", "wc", "-l", NULL) < 0)
+			die("execlp()");
+		
+		exit(EXIT_SUCCESS);
+	}
+	
+	return 0;
+}
-- 
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