Programming

int main()
{
    int Pipe[2];
    int origStdin, origStdout;
    int childPID;
    origStdin = dup(0);
    origStdout = dup(1);
    pipe(Pipe);
    if( (childPID = fork()) < 0 )
    {
        perror( "Fork Error" );
        exit(-1);
    }
    if( !childPID )
    {
        dup2( Pipe[0], 0 );
        dup2( origStdout, 1 );
        close( origStdout );
        close( origStdin );
        close( Pipe[0] );
        close( Pipe[1] );
        execlp( "/bin/sort", "sort", NULL );
        perror("Execl error");
        exit(-1);
    }
    dup2( Pipe[1], 1 );
    close( Pipe[0] );
    close( Pipe[1] );
    close( origStdout );
    close( origStdin );
    execlp( "/bin/cat", "cat","a.txt","b.txt", NULL );
    perror( "EXEC Error");
    return 0;
}