Add lab 2 demos

lab2/demos/Makefile_bad

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+SHELL=/bin/bash
+CC=gcc
+CFLAGS=-std=c99 -Wall -Wextra -D_POSIX_C_SOURCE=201112L
+
+.PHONY: all clean
+
+all: server client
+
+server: server.c
+
+client: client.c
+
+clean:
+	$(RM) server client

lab2/demos/Makefile_good

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+all: server client
+
+server: server.c
+	gcc -Wall -Wextra -Werror -D_POSIX_C_SOURCE=201112L -o server server.c
+
+client: client.c
+	gcc -Wall -Wextra -Werror -D_POSIX_C_SOURCE=201112L -o client client.c
+
+clean:
+	rm -f server client

lab2/demos/duplicate_fd.c

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+#include <stdlib.h>
+#include <unistd.h>
+#include <stdio.h>
+#include <fcntl.h>
+
+int main(void) {
+    int fd = open("test.txt", O_CREAT | O_WRONLY);
+
+    if(fd < 0) {
+        printf("Error opening the file\n");
+    }
+
+    dup2(fd, 1);
+    printf("Tester\n");
+
+    close(fd);
+}

lab2/demos/pipe.c

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+#include <stdlib.h>
+#include <unistd.h>
+#include <stdio.h>
+#include <fcntl.h>
+
+int main(void) {
+    char buf[100];
+    char msg[] = "Mario";
+
+    int p[2];
+    pipe(p);
+
+    write(p[1], msg, sizeof(msg));
+    read(p[0], buf, sizeof(msg));
+
+    printf("Out from the pipe: `%s`\n", buf);
+}