58 lines
1.2 KiB
C
58 lines
1.2 KiB
C
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/*
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program runs "ls | sort" command using 2 child processes
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dup2 is used to duplicate an old file descriptor into a new one
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normal file descriptor table
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0 [ standard input ]
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1 [ standard output ]
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2 [ standard error ]
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pipe is used to communicate between child processes
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unused ends of the pipe should be closed if unused
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in that process
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*/
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#include <stdio.h>
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#include <string.h>
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#include <unistd.h>
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#include <sys/types.h>
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#include <sys/wait.h>
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int main()
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{
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int fds[2];
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pipe(fds);
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// Child 1 will duplicate downstream into stdin
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if(fork() == 0)
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{
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dup2(fds[0], 0); // normally 0 is for stdin
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// will now read to fds[0]
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// end of pipe
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close(fds[1]); // close other end of pipe
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execlp("sort", "sort", 0);
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//execlp("wc", "wc", "-l", 0); // Note the first argument is the command
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// After it are the arguments including
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// original command
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}
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// Child2 duplicates upstream into stdout
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else if (fork() == 0)
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{
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dup2(fds[1], 1); // normally 1 is for stdout
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// will now write to fds[1]
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// end of pipe
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close(fds[0]); // close other end of pipe
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execlp("ls", "ls", 0);
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}
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// Parent
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else
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{
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close(fds[0]);
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close(fds[1]);
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wait(0);
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wait(0);
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}
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}
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