Byr*_*sco 2 c linux redirect fork pipe
我现在正在编写自己的shell作为一个类的项目,并且一切都在工作.我的问题是我的管道,有时他们工作,有时,他们只是挂起,直到我打断他们.我已经对此进行了研究,似乎写入stdin的函数没有从第一个进程接收到EOF; 通常我已经知道问题是管道没有被关闭,但我的代码并不是这种情况(据我所知).
所有重定向工作及其任何变化:
ls -l > file1wc < file1 > file2以下管道命令有效:
w | head -n 4w | head -n 4 > file1这不起作用:ls | grep file1它显示正确的输出并且永远不会结束,除非用户向其发送中断信号.ls | grep file1 > file2也行不通.它挂起而不显示输出,创建file2,但从不写入它.
无论如何,我希望有一些我错过了别人可以注意到的东西; 我已经有一段时间了.如果我能提供更多代码,请告诉我.我在下面发布的代码是主文件,没有删除.
/*
* This code implemenFts a simple shell program
* At this time it supports just simple commands with
* any number of args.
*/
#include <stdio.h>
#include <unistd.h>
#include <sys/types.h>
#include <errno.h>
#include <signal.h>
#include <sys/wait.h>
#include <fcntl.h>
#include <sys/stat.h>
#include <stdlib.h>
#include <string.h>
#include "input.h"
#include "myShell.h"
#include "BackgroundStack.h"
/*
* The main shell function
*/
main() {
char *buff[20];
char *inputString;
BackgroundStack *bgStack = malloc(sizeof(BackgroundStack));
initBgStack(bgStack);
struct sigaction new_act;
new_act.sa_handler = sigIntHandler;
sigemptyset ( &new_act.sa_mask );
new_act.sa_flags = SA_RESTART;
sigaction(SIGINT, &new_act, NULL);
// Loop forever
while(1) {
const char *chPath;
doneBgProcesses(bgStack);
// Print out the prompt and get the input
printPrompt();
inputString = get_my_args(buff);
if (buff[0] == NULL) continue;
if (buff[0][0] == '#') continue;
switch (getBuiltInCommand(buff[0])) {
case EXIT:
exit(0);
break;
case CD:
chPath = (buff[1]==NULL) ? getenv("HOME") : buff[1];
if (chdir(chPath) < 0) {
perror(": cd");
}
break;
default:
do_command(buff, bgStack);
}
//free up the malloced memory
free(inputString);
}// end of while(1)
}
static void sigIntHandler (int signum) {}
/*
* Do the command
*/
int do_command(char **args, BackgroundStack *bgStack) {
int status, statusb;
pid_t child_id, childb_id;
char **argsb;
int pipes[2];
int isBgd = isBackgrounded(args);
int hasPipe = hasAPipe(args);
if (isBgd) removeBackgroundCommand(args);
if (hasPipe) {
int cmdBi = getSecondCommandIndex(args);
args[cmdBi-1] = NULL;
argsb = &args[cmdBi];
pipe(pipes);
}
// Fork the child and check for errors in fork()
if((child_id = fork()) == -1) {
switch(errno) {
case EAGAIN:
perror("Error EAGAIN: ");
return;
case ENOMEM:
perror("Error ENOMEM: ");
return;
}
}
if (hasPipe && child_id != 0) {
childb_id = fork();
if(childb_id == -1) {
switch(errno) {
case EAGAIN:
perror("Error EAGAIN: ");
return;
case ENOMEM:
perror("Error ENOMEM: ");
return;
}
}
}
if(child_id == 0 || (childb_id == 0 && hasPipe)) {
if (child_id != 0 && hasPipe) args = argsb;
if (child_id == 0 && isBgd) {
struct sigaction new_act;
new_act.sa_handler = SIG_IGN;
sigaction(SIGINT, &new_act, 0);
}
if (child_id == 0 && hasPipe) {
if (dup2(pipes[1], 1) != 1) fatalPerror(": Pipe Redirection Output Error");
close(pipes[0]);
close(pipes[1]);
}
if (child_id != 0 && hasPipe) {
if (dup2(pipes[0], 0) != 0) fatalPerror(": Pipe Redirection Input Error");
close(pipes[0]);
close(pipes[1]);
waitpid(child_id, NULL, 0);
}
if ((child_id != 0 && hasPipe) || !hasPipe) {
if (hasAReOut(args)) {
char outFile[100];
getOutFile(args, outFile);
int reOutFile = open(outFile, O_RDWR|O_CREAT|O_TRUNC, S_IREAD|S_IWRITE);
if (reOutFile<0) fatalPerror(": Redirection Output Error");
if (dup2(reOutFile,1) != 1) fatalPerror(": Redirection Output Error");
close(reOutFile);
}
}
if ( (child_id == 0 && hasPipe) || !hasPipe) {
if (hasAReIn(args)) {
char inFle[100];
getInFile(args, inFle);
int reInFile = open(inFle, O_RDWR);
if (reInFile<0) fatalPerror(": Redirection Input Error");
if (dup2(reInFile,0) != 0) fatalPerror(": Redirection Input Error");
close(reInFile);
} else if (isBgd && !hasPipe) {
int bgReInFile = open("/dev/null", O_RDONLY);
if (bgReInFile<0) fatalPerror(": /dev/null Redirection Input Error");
if (dup2(bgReInFile,0) != 0) fatalPerror(": /dev/null Redirection Input Error");
close(bgReInFile);
}
}
// Execute the command
execvp(args[0], args);
perror(args[0]);
exit(-1);
}
// Wait for the child process to complete, if necessary
if (!isBgd) waitpid(child_id, &status, 0);
else if (!hasPipe) {
printf("Child %ld started\n", (long)child_id);
BackgroundProcess *bgPrs = malloc(sizeof(BackgroundProcess));
bgPrs->pid = child_id;
bgPrs->exitStatus = -1;
addProcessToBgStack(bgStack, bgPrs);
}
if (hasPipe) waitpid(childb_id, &statusb, 0);
if ( WIFSIGNALED(status) && !isBgd ) printf("Child %ld terminated due to signal %d\n", (long)child_id, WTERMSIG(status) );
if ( hasPipe && WIFSIGNALED(statusb) ) printf("Child %ld terminated due to signal %d\n", (long)childb_id, WTERMSIG(status) );
} // end of do_command
第二个孩子应该不是等待第一个孩子退出-它应该只是开始运行直线距离(它会阻塞,直到有输出由第一个孩子在管道生产),因此删除waitpid()的执行childb.相反,父进程应该等待两个子进程(或者可能只是第二个进程).(事实上,正如JeremyP所指出的那样,这个waitpid()电话无论如何都是失败的,因为childb它不是父母的child).
但是,您的问题是父进程主要向管道提供打开的文件描述符.在注释之前// Wait for the child process to complete, if necessary,父进程应该关闭其管道文件描述符:
close(pipes[0]);
close(pipes[1]);
父级中的打开文件描述符意味着子grep进程永远不会看到EOF,因此它不会退出.