Modify Program 5.2 so that three commands, last, sort, and more can be passed to the program from command line. Each command passed to the program should be connected to the next command via a pipe. Recommend to use execvp() when running last, sort and more. When use this new program a three-command sequence such as:

%last | sort | more would be indicated as:

% ./a.out last sort more

when running your program.

Program 5.2 is as follows:

/*

*A last | sort command pipeline

*/

#include

#include

#include

int

main(void) {

int f_des[2];

if (pipe(f_des) == -1) {

perror(Pipe); exit(1);

}

switch (fork()) {

case -1: perror(Fork); exit(2);

case 0: /*In the child process */

dup2(f_des[1], fileno(stdout));

close(f_des[0]); close(f_des[1]);

execl(/usr/bin/last, last, (char *) 0);

exit(3);

default:

dup2(f_des[0], fileno(stdin));

close(f_des[0]); close(f_des[1]);

execl(/bin/sort, sort, (char *) 0);

exit(4);

}

}