//pipe1.cpp #include  #include  #include  #include  #include  using namespace std; int main() { FILE *fpi; //for reading a pipe char buffer[BUFSIZ+1]; //BUFSIZ defined in  int chars_read; memset ( buffer, 0,sizeof(buffer)); //clear buffer fpi = popen ( "ps -auxw", "r" ); //pipe to command "ps -auxw" if ( fpi != NULL ) { //read data from pipe into buffer chars_read = fread(buffer, sizeof(char), BUFSIZ, fpi ); if ( chars_read > 0 ) cout << "Output from pipe: " << buffer << endl; pclose ( fpi ); //close the pipe return 0; } return 1; } 

What do you see when you execute "pipe1" ? Why? Modify the program pipe1.cpp to pipe1a.cpp so that it accepts a command (e.g. "ls -l") from the keyboard. For example, when you execute "./pipe1a ps -auxw", it should give you the same output as pipe1.cpp. (Hint: Use string functions strcpy() and strcat() to store the commands in a buffer. Your main function should be like: int main( int argc, char *argv[] ) )

You can also send output to an external program via a pipe. Try the following program:

//pipe2.cpp #include  #include  #include  #include  #include  using namespace std; int main() { FILE *fpo; //for writing to a pipe char buffer[BUFSIZ+1]; //BUFSIZ defined in  //Write buffer a message sprintf(buffer, "Arnod said, 'If I am elected, ..', and the fairy tale begins "); fpo = popen ( "od -c", "w" ); //pipe to command "od -c" //od -- output dump, see "man od" if ( fpo != NULL ) { //send data from buffer to pipe fwrite(buffer, sizeof(char), strlen(buffer), fpo ); pclose ( fpo ); //close the pipe return 0; } return 1; } 

What do you see when you execute "pipe2" ? Why? Modify the program so that it prints out the first three words of the sentence in reverse by making use of awk (see lab 2) (i.e. 'If said, Arnod....).