First commit

1stfile.txt

@@ -0,0 +1,6 @@
+aaa
+bbb
+ccc
+ddd
+eee
+fff

2ndfile.txt

@@ -0,0 +1,4 @@
+bbb
+ccc
+eee
+fff

3rdfile.txt

@@ -0,0 +1,2 @@
+aaa
+ddd

DD.c

@@ -0,0 +1,69 @@
+#include <stdio.h>
+#include <string.h>
+#include <stdlib.h>
+#include <sys/types.h>
+#include <unistd.h>
+#include <signal.h>
+
+int main (int argc, char *argBB[]) {
+
+    int C3, waitVal, waitVal2, ps;
+    C3 = fork(); 
+
+    if(C3 < 0)
+    {
+        printf("Fork failed");
+        exit(1);
+    }
+
+    if(C3 != 0)
+    {
+        printf("\nPid = %d Code DD: created proccess Pid = %d (code CC)\n", getpid(), C3);
+    }
+    if( C3 == 0 )
+    {
+        if( execv("CC", 0) == -1 ){
+            printf("\nexecv failed\n");
+            exit(0);
+        }
+    }
+
+
+    ps = fork();
+    if(ps < 0)
+    {
+        printf("Fork failed");
+        exit(1);
+    }
+
+    if(ps != 0)
+    {
+        printf("\nPid = %d Code DD: created proccess Pid = %d (code ps)\n", getpid(), ps);
+    }
+
+    if( ps == 0 )
+    {
+        char command[50];
+        strcpy(command, "ps -u username");
+        system(command);    
+        exit(11);
+        kill(ps, SIGKILL);//KILL PROCCESS PS HERE
+    }
+
+    waitVal = wait(&waitVal2);
+
+    if(waitVal == ps)
+    {
+        printf("\nPid= %d Code DD: process Pid = %d terminated\n", getpid(), ps);
+        printf("\nPid = %d Code DD: killing process Pid = %d\n", getpid(), C3);
+        kill(C3, SIGKILL);
+        printf("\nPid= %d Code DD: process Pid = %d terminated\n", getpid(), C3);
+        printf("\nPid = %d Code DD: terminating\n", getpid());
+        exit(7);
+    }
+
+    return 0;
+
+
+
+}

Head First C/ch 10/diner.c

@@ -0,0 +1,16 @@
+#include <stdio.h>
+#include <stdlib.h>
+
+int
+main( int argc, char *argv[])
+{
+    int i;
+    printf("# of Diners:%i\n", atoi(argv[1]) );
+
+    for( i = 2; i < (atoi)(argv[1]) + 2; i ++ )
+        printf( "Dish: %s\n", argv[i] );
+
+    printf( "DRINK: %s\n", getenv("DRINK"));
+
+    return 0;
+}

Head First C/ch 10/dup2_fileno.c

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+// Jan 29, 17
+//
+// Demonstration of fork() and execle() command.
+// By using child process, now it goes thru all three loop.
+// But still there is a problem. 
+// These child processes overlap each other.
+// In order to resolve this overlap problem, we need to make sure
+// each child process terminates before starting a new process.
+// We do this with waitpid() command.
+// Furthermore, we use dup2() command to redirect the stdout to
+// a text file.
+// The text file looks like as follows:
+/*
+# of Diners:2
+# of Diners:2
+Dish: chicken
+Dish: chicken
+Dish: beef
+Dish: beef
+DRINK: COKE
+DRINK: ORANGE JUICE
+# of Diners:2
+Dish: chicken
+Dish: beef
+DRINK: ICE-TEA
+*/
+#include <sys/wait.h>
+#include <stdio.h>
+#include <unistd.h>
+#include <errno.h>
+#include <stdlib.h>
+
+void
+error( char *msg )
+{
+    fprintf( stderr, "%s: %d\n", msg, strerror(errno));
+    //exit(1);
+}
+
+int
+main()
+{
+
+    char *drinks[] = { "ORANGE JUICE", "COKE", "ICE-TEA" };
+    char drink[50];
+
+    int i, pid_status;
+    FILE *f = fopen( "output.txt", "w");
+
+    if( !f ){
+        error( "Cannot open a file to write.");
+    }
+
+
+    for( i=0; i<3; i++ ){
+        sprintf( drink, "DRINK=%s", drinks[i] );
+        char *myEnv[] = { drink, NULL };
+
+        pid_t pid = fork();
+
+        if( pid == -1 ){
+            error( "Can't fork process. \n" );
+        }
+
+        if( !pid ){
+
+            printf( "file number = %u\n", fileno(f));
+
+            if( dup2( fileno(f), 1) == -1 ){
+                    error( "Can't redirect Standard output");
+
+                    perror("dup2 failed");
+            }
+            if( execle( "/home/ubuntu/workspace/Head First C/ch 9/diner", "/home/ubuntu/workspace/Head First C/ch 9/diner", "2", "chicken", "beef", NULL, myEnv ) == -1 )
+            {
+                error( "Cannot run diner\n");
+            }
+            if( waitpid(pid, &pid_status, 0) == -1 ){
+                error( "Error waiting for child process" );
+            }
+        }
+    }
+    return 0;
+}

Head First C/ch 10/output.txt

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+# of Diners:2
+Dish: chicken
+Dish: beef
+DRINK: COKE
+# of Diners:2
+Dish: chicken
+Dish: beef
+DRINK: ICE-TEA
+# of Diners:2
+Dish: chicken
+Dish: beef
+DRINK: ORANGE JUICE

Head First C/ch 10/pipe.c

@@ -0,0 +1,120 @@
+// Jan 29, 17
+//
+// Exercising fork() and execle() and dup2() and pipe command.
+// By using child process, now it goes thru all three loop.
+// But still there is a problem. 
+// These child processes overlap each other.
+// In order to resolve this overlap problem, we need to make sure
+// each child process terminates before starting a new process.
+// We do this with waitpid() command.
+// Furthermore, we use dup2() command to redirect the stdout to
+// a text file.
+// The text file looks like as follows:
+//
+// This program takes one step further by creating a pipe between
+// child and parent process.  The stdout of the child process is
+// piped to stdin of the parent process.
+/*
+parents: # of Diners:2
+
+parents: Dish: chicken
+
+parents: Dish: beef
+
+parents: DRINK: ORANGE JUICE
+
+parents: # of Diners:2
+
+parents: Dish: chicken
+
+parents: Dish: beef
+
+parents: DRINK: COKE
+
+parents: # of Diners:2
+
+parents: Dish: chicken
+
+parents: Dish: beef
+
+parents: DRINK: ICE-TEA
+
+*/
+#include <sys/wait.h>
+#include <stdio.h>
+#include <unistd.h>
+#include <errno.h>
+#include <stdlib.h>
+
+void
+error( char *msg )
+{
+    fprintf( stderr, "%s: %d\n", msg, strerror(errno));
+    //exit(1);
+}
+
+int
+main()
+{
+
+    char *drinks[] = { "ORANGE JUICE", "COKE", "ICE-TEA" };
+    char drink[50];
+
+    int fd[2];
+
+    int i, pid_status;
+
+
+
+    for( i=0; i<3; i++ ){
+        if( pipe(fd) == -1 ){
+            error( "Cannot create a pipe.\n" );
+        }
+
+        sprintf( drink, "DRINK=%s", drinks[i] );
+        char *myEnv[] = { drink, NULL };
+
+        pid_t pid = fork();
+
+        if( pid == -1 ){
+            error( "Can't fork process. \n" );
+        }
+
+        if( !pid ){
+
+            //close reading end of the pipe.
+            close(fd[0]);
+            //make STDOUT same as the pipe writing.
+            //In other words, what ever is written on STDOUT will be written to the pipe.
+            //STDOUT equals to writing end of the PIPE.
+            if( dup2( fd[1], 1) == -1 ){
+                    error( "Can't redirect Standard output");
+
+                    perror("dup2 failed");
+            }
+            if( execle( "/home/ubuntu/workspace/Head First C/ch 9/diner", "/home/ubuntu/workspace/Head First C/ch 9/diner", "2", "chicken", "beef", NULL, myEnv ) == -1 )
+            {
+                error( "Cannot run diner\n");
+            }
+            if( waitpid(pid, &pid_status, 0) == -1 ){
+                error( "Error waiting for child process" );
+            }
+        }
+
+
+        //Whatever written is written to the pipe will be considered as STDIN.
+        //STDIN = reading end of the pipe.
+        dup2(fd[0], 0);
+
+        //Close the written end of the pipe.
+        //This part is needed.  Without it, this works only for the first loop.
+        close(fd[1]);
+
+        char line[255];
+
+        while( fgets(line, 255, stdin) ){
+            printf("parents: %s\n", line);
+        }
+    }
+    return 0;
+}