这是我的代码：
#include <stdio.h>
#include <stdlib.h>
#include <unistd.h>
#include <wait.h>
#include <readline/readline.h>
#define NUMPIPES 2
int main(int argc,char *argv[]) {
char *bBuffer,*sPtr,*aPtr = NULL,*pipeComms[NUMPIPES],*cmdArgs[10];
int fdPipe[2],pCount,aCount,i,status,lPids[NUMPIPES];
pid_t pid;
pipe(fdPipe);
while(1) {
bBuffer = readline("Shell> ");
if(!strcasecmp(bBuffer,"exit")) {
return 0;
}
sPtr = bBuffer;
pCount = -1;
do {
aPtr = strsep(&sPtr,"|");
pipeComms[++pCount] = aPtr;
} while(aPtr);
for(i = 0; i < pCount; i++) {
aCount = -1;
do {
aPtr = strsep(&pipeComms[i]," ");
cmdArgs[++aCount] = aPtr;
} while(aPtr);
cmdArgs[aCount] = 0;
if(strlen(cmdArgs[0]) > 0) {
pid = fork();
if(pid == 0) {
if(i == 0) {
close(fdPipe[0]);
dup2(fdPipe[1],STDOUT_FILENO);
close(fdPipe[1]);
} else if(i == 1) {
close(fdPipe[1]);
dup2(fdPipe[0],STDIN_FILENO);
close(fdPipe[0]);
}
execvp(cmdArgs[0],cmdArgs);
exit(1);
} else {
lPids[i] = pid;
/*waitpid(pid,&status,0);
if(WIFEXITED(status)) {
printf("[%d] TERMINATED (Status: %d)\n",pid,WEXITSTATUS(status));
}*/
}
}
}
for(i = 0; i < pCount; i++) {
waitpid(lPids[i],0);
if(WIFEXITED(status)) {
printf("[%d] TERMINATED (Status: %d)\n",lPids[i],WEXITSTATUS(status));
}
}
}
return 0;
}
(代码更新,以反映他提出的两个答案下面的变化,它仍然不工作,因为它应该…)
以下是测试用例：
nazgulled ~/Projects/SO/G08 $ls -l total 8 -rwxr-xr-x 1 nazgulled nazgulled 7181 2009-05-27 17:44 a.out -rwxr-xr-x 1 nazgulled nazgulled 754 2009-05-27 01:42 data.h -rwxr-xr-x 1 nazgulled nazgulled 1305 2009-05-27 17:50 main.c -rwxr-xr-x 1 nazgulled nazgulled 320 2009-05-27 01:42 makefile -rwxr-xr-x 1 nazgulled nazgulled 14408 2009-05-27 17:21 prog -rwxr-xr-x 1 nazgulled nazgulled 9276 2009-05-27 17:21 prog.c -rwxr-xr-x 1 nazgulled nazgulled 10496 2009-05-27 17:21 prog.o -rwxr-xr-x 1 nazgulled nazgulled 16 2009-05-27 17:19 test nazgulled ~/Projects/SO/G08 $./a.out Shell> ls -l|grep prog [4804] TERMINATED (Status: 0) -rwxr-xr-x 1 nazgulled nazgulled 14408 2009-05-27 17:21 prog -rwxr-xr-x 1 nazgulled nazgulled 9276 2009-05-27 17:21 prog.c -rwxr-xr-x 1 nazgulled nazgulled 10496 2009-05-27 17:21 prog.o
问题是我应该回到我的shell之后,我应该看到“Shell>”等待更多的输入.您还可以注意到,您没有看到类似于“[4804] TERMINATED(Status：0)”(但使用不同的pid)的消息,这意味着第二个进程没有终止.
我认为这与grep有关,因为这有用：
nazgulled ~/Projects/SO/G08 $./a.out Shell> echo q|sudo fdisk /dev/sda [4838] TERMINATED (Status: 0) The number of cylinders for this disk is set to 1305. There is nothing wrong with that,but this is larger than 1024,and Could in certain setups cause problems with: 1) software that runs at boot time (e.g.,old versions of LILO) 2) booting and partitioning software from other OSs (e.g.,DOS FdisK,OS/2 FdisK) Command (m for help): [4839] TERMINATED (Status: 0)
你可以很容易地看到两个“终止”消息…
那么我的代码怎么了？
解决方法
即使您的管道的第一个命令退出(并且thust关闭stdout =〜fdPipe [1]),父进程仍然有fdPipe [1]打开.
因此,管道的第二个命令有一个stdin =〜fdPipe [0],它永远不会得到EOF,因为管道的另一个端点仍然是打开的.
您需要为每个|创建一个新的管道(fdPipe),并确保关闭父项中的两个端点;即
for cmd in cmds
if there is a next cmd
pipe(new_fds)
fork
if child
if there is a prevIoUs cmd
dup2(old_fds[0],0)
close(old_fds[0])
close(old_fds[1])
if there is a next cmd
close(new_fds[0])
dup2(new_fds[1],1)
close(new_fds[1])
exec cmd || die
else
if there is a prevIoUs cmd
close(old_fds[0])
close(old_fds[1])
if there is a next cmd
old_fds = new_fds
if there are multiple cmds
close(old_fds[0])
close(old_fds[1])
另外,为了更安全,在执行任何关闭和dup2操作之前,应该处理fdPipe和{STDIN_FILENO,STDOUT_FILENO}重叠的情况.如果有人设法用stdin或stdout关闭来启动shell,这可能会发生,并且会导致这里的代码很混乱.
编辑
fdPipe1 fdPipe3
v v
cmd1 | cmd2 | cmd3 | cmd4 | cmd5
^ ^
fdPipe2 fdPipe4
除了确保关闭管道在父级中的端点之外,我试图说明fdPipe1,fdPipe2等不能是同一个pipe().
/* suppose stdin and stdout have been closed...
* for example,if your program was started with "./a.out <&- >&-" */
close(0),close(1);
/* then the result you get back from pipe() is {0,1} or {1,0},since
* fd numbers are always allocated from the lowest available */
pipe(fdPipe);
close(0);
dup2(fdPipe[0],0);
我知道你现在不用close(0),但最后一段警告你要注意这种情况.
编辑
以下对您的代码的最小更改使其在您提到的特定故障案例中起作用：
@@ -12,6 +12,4 @@
pid_t pid;
- pipe(fdPipe);
-
while(1) {
bBuffer = readline("Shell> ");
@@ -29,4 +27,6 @@
} while(aPtr);
+ pipe(fdPipe);
+
for(i = 0; i < pCount; i++) {
aCount = -1;
@@ -72,4 +72,7 @@
}
+ close(fdPipe[0]);
+ close(fdPipe[1]);
+
for(i = 0; i < pCount; i++) {
waitpid(lPids[i],0);
这对于管道中的多个命令不起作用;为此,你需要这样的东西：(未经测试,因为你必须修复其他的东西)
@@ -9,9 +9,7 @@
int main(int argc,char *argv[]) {
char *bBuffer,*cmdArgs[10];
- int fdPipe[2],lPids[NUMPIPES];
+ int fdPipe[2],fdPipe2[2],lPids[NUMPIPES];
pid_t pid;
- pipe(fdPipe);
-
while(1) {
bBuffer = readline("Shell> ");
@@ -32,4 +30,7 @@
aCount = -1;
+ if (i + 1 < pCount)
+ pipe(fdPipe2);
+
do {
aPtr = strsep(&pipeComms[i]," ");
@@ -43,11 +44,12 @@
if(pid == 0) {
- if(i == 0) {
- close(fdPipe[0]);
+ if(i + 1 < pCount) {
+ close(fdPipe2[0]);
- dup2(fdPipe[1],STDOUT_FILENO);
+ dup2(fdPipe2[1],STDOUT_FILENO);
- close(fdPipe[1]);
- } else if(i == 1) {
+ close(fdPipe2[1]);
+ }
+ if(i != 0) {
close(fdPipe[1]);
@@ -70,17 @@
}
}
+
+ if (i != 0) {
+ close(fdPipe[0]);
+ close(fdPipe[1]);
+ }
+
+ fdPipe[0] = fdPipe2[0];
+ fdPipe[1] = fdPipe2[1];
+ }
+
+ if (pCount) {
+ close(fdPipe[0]);
+ close(fdPipe[1]);
}