我无法想出任何一种在C语言中实现管道的方法，这也是我决定在这里写下来的原因。我必须承认，我知道管道/分叉/命名管道的工作原理。我已经看到了很多实现2-3个管道的例子，这很容易。但问题出现在我需要实现一个shell，并且管道数量是未知的时候。
目前我所拥有的：
ls -al | tr a-z A-Z | tr A-Z a-z | tr a-z A-Z
我将这行文字转化为如下格式：
array[0] = {"ls", "-al", NULL"}
array[1] = {"tr", "a-z", "A-Z", NULL"}
array[2] = {"tr", "A-Z", "a-z", NULL"}
array[3] = {"tr", "a-z", "A-Z", NULL"}
因此，我可以使用。
execvp(array[0],array)
稍后再说。
直到现在，我相信一切都很好。问题出现在我试图将这些功能的输入/输出互相重定向时。
以下是我的做法：
mkfifo("queue", 0777);
for (i = 0; i<= pipelines_count; i++) // eg. if there's 3 pipelines, there's 4 functions to execvp
{
int b = fork();
if (b == 0) // child
{
int c = fork();
if (c == 0)
// baby (younger than child)
// I use c process, to unblock desc_read and desc_writ for b process only
// nothing executes in here
{
if (i == 0) // 1st pipeline
{
int desc_read = open("queue", O_RDONLY);
// dup2 here, so after closing there's still something that can read from
// from desc_read
dup2(desc_read, 0);
close(desc_read);
}
if (i == pipelines_count) // last pipeline
{
int desc_write = open("queue", O_WRONLY);
dup2(desc_write, 0);
close(desc_write);
}
if (i > 0 && i < pipelines_count) // pipeline somewhere inside
{
int desc_read = open("queue", O_RDONLY);
int desc_write = open("queue", O_WRONLY);
dup2(desc_write, 1);
dup2(desc_read, 0);
close(desc_write);
close(desc_read);
}
exit(0); // closing every connection between process c and pipeline
}
else
// b process here
// in b process, i execvp commands
{
if (i == 0) // 1st pipeline (changing stdout only)
{
int desc_write = open("queue", O_WRONLY);
dup2(desc_write, 1); // changing stdout -> pdesc[1]
close(desc_write);
}
if (i == pipelines_count) // last pipeline (changing stdin only)
{
int desc_read = open("queue", O_RDONLY);
dup2(desc_read, 0); // changing stdin -> pdesc[0]
close(desc_read);
}
if (i > 0 && i < pipelines_count) // pipeline somewhere inside
{
int desc_write = open("queue", O_WRONLY);
dup2(desc_write, 1); // changing stdout -> pdesc[1]
int desc_read = open("queue", O_RDONLY);
dup2(desc_read, 0); // changing stdin -> pdesc[0]
close(desc_write);
close(desc_read);
}
wait(NULL); // it wait's until, process c is death
execvp(array[0],array);
}
}
else // parent (waits for 1 sub command to be finished)
{
wait(NULL);
}
}
感谢您的选择。