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我在學習管道,並且出現了問題。我想我的程序工作如下:
grep [word to find] [file to search] | grep -i [without word] | wc -l
它編譯和工作沒有錯誤,但它沒有輸出(至少不是我想要它做的stdout)。奇怪的是,當我嘗試在最後一個fork中打印它時,它在stdin上打印它。我不改變這個叉或在parrent過程中的標準輸出,所以它對我來說似乎很奇怪。我試圖關閉未使用的管道並刷新標準輸出(這是否仍然在這裏?),但是可能還有更多的事情要做。進程通信中的管道標準輸入/標準輸出。
#include<stdio.h>
#include<stdlib.h>
#include<unistd.h>
void help() {
printf("Usage of the program:\n"
"\t./alagrep [fileToSearch] [wordToFind] [wordToExpel]\n");
}
int main(int argc, char *argv[]) {
if(argc != 4) {
help();
exit(EXIT_FAILURE);
}
int fd[2];
if(pipe(fd) != 0) {
printf("Error while opening a pipe.\n");
exit(EXIT_FAILURE);
}
pid_t pid;
if((pid = fork()) == -1) {
printf("Error while forking.\n");
exit(EXIT_FAILURE);
} else if(pid == 0) {
close(fd[0]);
if(dup2(fd[1],STDOUT_FILENO) < 0) {
printf("Cannot duplicate stdout.\n");
_exit(EXIT_FAILURE);
}
close(fd[1]);
execl("/bin/grep","grep",argv[2],argv[1],NULL);
fflush(stdout);
}
close(fd[1]);
int fd1[2];
if(pipe(fd1) != 0) {
printf("Error while opening a pipe.\n");
exit(EXIT_FAILURE);
}
if((pid = fork()) == -1) {
printf("Error while forking.\n");
exit(EXIT_FAILURE);
} else if(pid == 0) {
close(fd1[0]);
if(dup2(fd[0],STDIN_FILENO) < 0) {
printf("Cannot duplicate stdin.\n");
_exit(EXIT_FAILURE);
}
if(dup2(fd1[1],STDOUT_FILENO) < 0) {
printf("Cannot duplicate stdout.\n");
_exit(EXIT_FAILURE);
}
close(fd[0]);
close(fd1[1]);
execl("/bin/grep","grep","-i",argv[3],NULL);
fflush(stdout);
}
close(fd[0]);
close(fd1[1]);
if((pid = fork()) == -1) {
printf("Error while forking.\n");
exit(EXIT_FAILURE);
} else if(pid == 0) {
close(fd1[1]);
if(dup2(fd1[0],STDIN_FILENO) < 0) {
printf("Cannot duplicate stdin.\n");
_exit(EXIT_FAILURE);
}
close(fd1[0]);
execl("/bin/wc","wc","-l",NULL);
fflush(stdout);
}
close(fd1[0]);
return 0;
}