1+ #include < iostream>
2+ #include < stdio.h>
3+ #include < stdlib.h>
4+ #include < unistd.h>
5+ #include < sys/types.h>
6+ #include < sys/wait.h>
7+ 8+ using namespace std ;
9+ 10+ struct CmdLine
11+ {
12+ char * value;
13+ char * arguments;
14+ CmdLine* next;
15+ };
16+ 17+ // Compilation:
18+ // g++ "03 - Nonamed_pipes.cpp" -o nonamedpipes
19+ 20+ // Task:
21+ // Create a program which works just like the command below:
22+ // $> who | sort | uniq -c | sort -nk1
23+ 24+ void run (CmdLine* command)
25+ {
26+ const int numPipes = 3 ;
27+ int i = 0 ;
28+ 29+ // Create all pipes.
30+ int pipefds[2 *numPipes];
31+ for (i = 0 ; i < (numPipes); i++)
32+ {
33+ if (pipe (pipefds + i*2 ) < 0 )
34+ {
35+ printf (" Couldn't create pipe %d\n " 1 );
36+ exit (EXIT_FAILURE);
37+ }
38+ }
39+ 40+ int j = 0 ;
41+ pid_t pid;
42+ while (command)
43+ {
44+ pid = fork ();
45+ if (pid == 0 )
46+ {
47+ // if not last command
48+ if (command->next )
49+ {
50+ if (dup2 (pipefds[j + 1 ], STDOUT_FILENO) < 0 )
51+ {
52+ perror (" dup2"
53+ exit (EXIT_FAILURE);
54+ }
55+ }
56+ 57+ // if not first command && j != 2*numPipes
58+ if (j != 0 )
59+ {
60+ if (dup2 (pipefds[j-2 ], STDIN_FILENO) < 0 )
61+ {
62+ perror (" dup2" // /j-2 0 j+1 1
63+ exit (EXIT_FAILURE);
64+ }
65+ }
66+ 67+ 68+ for (i = 0 ; i < 2 *numPipes; i++)
69+ {
70+ close (pipefds[i]);
71+ }
72+ 73+ // Command with or without arguments.
74+ if (command->arguments == NULL )
75+ {
76+ if ( execlp (command->value , command->value , NULL ) < 0 )
77+ {
78+ perror (command->value );
79+ exit (EXIT_FAILURE);
80+ }
81+ }
82+ else
83+ {
84+ if ( execlp (command->value , command->value , command->arguments , NULL ) < 0 )
85+ {
86+ perror (command->value );
87+ exit (EXIT_FAILURE);
88+ }
89+ }
90+ }
91+ else if (pid < 0 )
92+ {
93+ perror (" error"
94+ exit (EXIT_FAILURE);
95+ }
96+ 97+ command = command->next ;
98+ j+=2 ;
99+ }
100+ 101+ /* Parent closes the pipes and wait for children */
102+ for (i = 0 ; i < 2 * numPipes; i++)
103+ {
104+ close (pipefds[i]);
105+ }
106+ 107+ int status;
108+ for (i = 0 ; i < numPipes + 1 ; i++)
109+ {
110+ wait (&status);
111+ }
112+ }
113+ 114+ int main (int argc, char ** argv)
115+ {
116+ printf (" Result of operation is the same like if you type\n $>who | sort | uniq -c | sort -nk1\n "
117+ 118+ char sort[] = " sort"
119+ char sortArg[] = " -nk1"
120+ char uniq[] = " uniq"
121+ char uniqArg[] = " -c"
122+ char who[] = " who"
123+ 124+ CmdLine command4 = { sort, sortArg, NULL };
125+ CmdLine command3 = { uniq, uniqArg, &command4 };
126+ CmdLine command2 = { sort, NULL , &command3 };
127+ CmdLine command1 = { who, NULL , &command2 };
128+ 129+ run (&command1);
130+ 131+ return 0 ;
132+ }
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