rexim · January 30, 2021 14:16 · Jan 30, 2021
diff --git a/main.c b/main.c
@@ -0,0 +1,63 @@
+#include <assert.h>
+#include <stdio.h>
+#include <stdlib.h>
+#include <string.h>
+#include <errno.h>
+
+#include <sys/types.h>
+#include <sys/wait.h>
+#include <sys/stat.h>
+#include <unistd.h>
+#include <fcntl.h>
+
+#define ERR(expr)                                  \
+    do {                                           \
+        int err = expr;                            \
+        if (err < 0) {                             \
+            fprintf(stderr, "%s: %s\n", #expr, strerror(errno));    \
+            exit(1);                                                 \
+        }                                          \
+    } while (0)
+
+int main(void)
+{
+    // cat ./main.c | sort
+
+    int pipefd[2] = {0};
+
+    ERR(pipe(pipefd));
+
+    pid_t cpid = fork();
+    assert(cpid >= 0);
+
+    if (cpid == 0) {
+        int input = open(__FILE__, O_RDONLY);
+        assert(input >= 0);
+
+        ERR(close(pipefd[0]));
+        ERR(dup2(input, STDIN_FILENO));
+        ERR(dup2(pipefd[1], STDOUT_FILENO));
+        ERR(execlp("cat", "cat", NULL));
+    }
+
+    cpid = fork();
+    assert(cpid >= 0);
+
+    if (cpid == 0) {
+        int output = open("./output.txt", O_WRONLY | O_CREAT | O_TRUNC, S_IRUSR | S_IWUSR | S_IRGRP | S_IROTH);
+        assert(output >= 0);
+
+        ERR(close(pipefd[1]));
+        ERR(dup2(pipefd[0], STDIN_FILENO));
+        ERR(dup2(output, STDOUT_FILENO));
+        ERR(execlp("sort", "sort", NULL));
+    }
+
+    ERR(close(pipefd[0]));
+    ERR(close(pipefd[1]));
+
+    ERR(wait(NULL));
+    ERR(wait(NULL));
+
+    return 0;
+}