Added Topic 6

Topic-6/task_6_1.c

@@ -0,0 +1,32 @@
+//
+// Written for Computer Networks and Systems lab classes
+// AUTHOR : Sergiusz Warga
+
+#include <stdio.h>
+#include <sys/types.h>
+#include <unistd.h>
+#include <stdlib.h>
+
+void child_task() {
+    execl("/usr/bin/cal", "cal", "2021", NULL);
+}
+
+int main() {
+    pid_t pid;
+    int status;
+
+    pid = fork();
+
+    if (pid == -1) {    // If something went wrong.
+        perror("Fork: ");
+        exit(EXIT_FAILURE);
+    }
+
+    if (pid == 0) {     // If this is a child process.
+        child_task();
+        exit(EXIT_SUCCESS);
+    }
+
+    wait(&status);
+    return 0;
+}

Topic-6/task_6_2.c

@@ -0,0 +1,17 @@
+//
+// Written for Computer Networks and Systems lab classes
+// AUTHOR : Sergiusz Warga
+
+#include <stdio.h>
+#include <unistd.h>
+
+int main() {
+	char msg_write[] = "write() to dup(1)\n";
+	int soutfd = dup(STDOUT_FILENO);
+	write(soutfd, msg_write, sizeof(msg_write));
+
+	FILE *fakeout = fdopen(soutfd, "w");
+	fprintf(fakeout, "using fprintf() on fakeout\n");
+
+	return 0;
+}

Topic-6/task_6_3.c

@@ -0,0 +1,44 @@
+//
+// Written for Computer Networks and Systems lab classes
+// AUTHOR : Sergiusz Warga
+
+#include <stdio.h>
+#include <stdlib.h>
+#include <sys/types.h>
+#include <sys/wait.h>
+#include <unistd.h>
+
+
+int main() {
+	int pipefd[2];
+	if (pipe(pipefd) < 0) {
+		fprintf(stderr, "Something went wrong!\n");
+		return -1;
+	}
+
+	pid_t pid;
+	pid = fork();
+
+	if (pid == -1) {		// If something went wrong.
+		perror("Fork: ");
+		exit(EXIT_FAILURE);
+	}
+
+	if (pid == 0) {			// If this is a child process.
+		dup2(pipefd[1], STDOUT_FILENO);
+		printf("printf() from a child\n");
+		close(pipefd[1]);
+		exit(EXIT_SUCCESS);
+	}
+
+	char buff[100] = {};
+
+	while (read(pipefd[0], &buff, sizeof(buff)) > 0) {
+		printf("PARENT: %s", buff);
+	}
+
+	int status;
+	wait(&status);
+
+	return 0;
+}

Topic-6/task_6_4.c

@@ -0,0 +1,44 @@
+//
+// Written for Computer Networks and Systems lab classes
+// AUTHOR : Sergiusz Warga
+
+#include <stdio.h>
+#include <stdlib.h>
+#include <sys/types.h>
+#include <sys/wait.h>
+#include <unistd.h>
+
+
+int main() {
+	int pipefd[2];
+	if (pipe(pipefd) < 0) {
+		fprintf(stderr, "Something went wrong!\n");
+		return -1;
+	}
+
+	pid_t pid;
+	pid = fork();
+
+	if (pid == -1) {		// If something went wrong.
+		perror("Fork: ");
+		exit(EXIT_FAILURE);
+	}
+
+	if (pid == 0) {			// If this is a child process.
+		dup2(pipefd[1], STDOUT_FILENO);
+		execl("/usr/bin/cal", "cal", NULL);
+		close(pipefd[1]);
+		exit(EXIT_SUCCESS);
+	}
+
+	char buff[200] = {};
+
+	while (read(pipefd[0], &buff, sizeof(buff)) > 0) {
+		printf("%s", buff);
+	}
+
+	int status;
+	wait(&status);
+
+	return 0;
+}