3. Copy a File Using Pipes: Implement a command (lastnameCP) that copies one fil

Question

3. Copy a File Using Pipes: Implement a command (lastnameCP) that copies one file (source) to another (destination) using pipes. This is a lab in C

Hint: A possible solution:

- Parent process creates a pipe then forks a child process:

The parent process opens and reads the input file, that was passed as an argument, and writes the data to the upstream end of a pipe.

The child process opens the output file, reads data from the pipe and writes it to the output file.

- When done, the parent process closes the upstream and the child closes downstream.

Explanation / Answer

**************************************************CODE********************************************************************

#include<stdio.h>
#include<sys/types.h>
#include<sys/stat.h>
#include<fcntl.h>
#include<string.h>
#include<stdlib.h>

//defining the buffer size
#define SIZE_OF_BUFFER 50

int main( int argc, char* argv[] ) {
  
int fpipe[2];
pid_t child_id;
  
//buffer to read the input file
char readBuffer[SIZE_OF_BUFFER];

//creating a pipe
pipe(fpipe);
  
//checking for valid number of parameters entered
if( argc != 3 ) {
printf("ERROR: Enter 2 parameters only. ");
exit(1);
}
//Source file received as argument 1
int sourceFile = open(argv[1], 0);

//Destination file received as argument 2,if file does not exist it will create one

int destinationFile = open(argv[2], O_RDWR|O_CREAT|O_APPEND, 0666);

//check if file is able to open or not
if (sourceFile == -1 || destinationFile == -1) {
printf("ERROR: Couldnt open file ");
exit(1);
}
//fork the child
child_id = fork();

if (child_id == 0) {
// inside the child prcocess
close(fpipe[1]);

while (read(fpipe[0], readBuffer, sizeof(readBuffer)) > 0) {
// Writing to the destination file from pipe
write(destinationFile, readBuffer, strlen(readBuffer) - 1);
}

close(fpipe[0]);
close(destinationFile);
}
else {
// inside the parent process
close(fpipe[0]);

// code to read from a text file and store in pipe
while (read(sourceFile, readBuffer, sizeof(readBuffer)) > 0) {
write(fpipe[1], readBuffer, sizeof(readBuffer));
memset(readBuffer, 0, SIZE_OF_BUFFER);
}

close(fpipe[1]);
close(sourceFile);
wait(NULL);
}
}

***************************************************CODE*********************************************************************

To create child process we use fork().
fork() returns :
a) <0 failed to create child process
b) =0 for child process
c) >0 parent process will execute.

pipe() is used for passing information from one process to another. It can be used in 2 way communication.

fpipe[0] is one end of pipe(read end) and fpipe[1] is another end(write end).

**********HOW TO RUN***************

copy the above code and store in .c file

first create an inputfile.txt with some message at the same location of this C file

run the following in ubuntu terminal

gcc filename.c

./a.out inputfile.txt outputfile.txt

check the output file

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