c - execve 失败 - 忽略退出语句

问题描述

fgets混合和execve在一起时我有一个奇怪的问题。

我有一个从文件中读取行并执行它们的函数，或者通过它自己的函数解析它们，或者使用execve. 为了简单起见，我的测试文件只有外部函数：

echo whoowhee
lx
ls
dir

第二个命令lx不存在，因此此时execve应该失败。

这是我从文件中读取的代码：

  while(fgets(line, 1024, testfile) != NULL){
    if(strlen(line) < 3){continue;}
    if(line[0] == '#'){continue;}

    printf("%s%s", value("PROMPT"), line); // Emulates the prompt

    //Terminates line at right place to simulate input
    line[strlen(line)-2] = '\0';

    execute(line);

    Var *prompt = retrieveVar("PROMPT");
    sprintf(prompt->value, "< Executing script... - [%s] > $ ", value("EXITCODE"));

    lineNo++; 
  }

这是我的 fork-exec 块：

  if(pid == 0){ // Child

    // For loop for using all paths
    for(int i = 0; i < pathn; i++){
      args[0] = paths[i];

      // Executes command path[i] with arguments args with environment envp
      execve(paths[i], args, envp);
    }

    perror("execve");
    exit(0);
  }
  else if(pid > 0){ //Parent
    current_pid = pid;

    if(setpgid(pid, pid) != 0) perror("setpid");

    // Waits if background flag not activated.
    if(BG == 0){
      // WUNTRACED used to stop waiting when suspended
      waitpid(current_pid, &status, WUNTRACED);

        if(WIFEXITED(status)){
          setExitcode(WEXITSTATUS(status));
        }
        else if(WIFSIGNALED(status)){
          printf("Process received SIGNAL %d\n", WTERMSIG(status));
        }
    }
  }
  else{
    perror("fork()");
  }

由于execve需要程序的绝对路径，paths是程序应该存在的可能路径的数组。BG说明进程是否应该在后台执行，value("EXITCODE")是进程的退出代码，并且execute是执行该行的函数.

现在，这是我运行测试文件时的输出，代码原样：

<Welcome to Eggshell> $ echo whoowhee
whoowhee
< Executing script... - [0] > $ lx
execve: No such file or directory
< Executing script... - [0] > $ ls
add-on  codecov.yml documentation  eggshell.c  LICENSE  Makefile        README.md  switch.sh      val.log
ci  createfile.txt  eggshell       eggshell.h  main.c   Makefile-Clang  src        testinput.txt
< Executing script... - [0] > $ dir
add-on  codecov.yml documentation  eggshell.c  LICENSE  Makefile        README.md  switch.sh      val.log
ci  createfile.txt  eggshell       eggshell.h  main.c   Makefile-Clang  src        testinput.txt
< Executing script... - [0] > $ dir
add-on  codecov.yml documentation  eggshell.c  LICENSE  Makefile        README.md  switch.sh      val.log
ci  createfile.txt  eggshell       eggshell.h  main.c   Makefile-Clang  src        testinput.txt

如您所见，dir运行两次。

如果我在文本文件中添加另一个无意义的命令，问题并不止于此：

echo whoowhee
lx
onetimesoneistwo
ls
dir

如果我尝试运行该函数，它最终会陷入无限循环。不仅如此，这一次它还会一遍又一遍地运行整个文件！

但是，如果我exit从fork-exec位中删除，然后重新运行该函数，就会出现以下结果：

<Welcome to Eggshell> $ echo whoowhee
whoowhee
< Executing script... - [0] > $ lx
execve: No such file or directory
< Executing script... - [0] > $ onetimesoneistwo
execve: No such file or directory
< Executing script... - [0] > $ ls
add-on  codecov.yml documentation  eggshell.c  LICENSE  Makefile        README.md  switch.sh      val.log
ci  createfile.txt  eggshell       eggshell.h  main.c   Makefile-Clang  src        testinput.txt
< Executing script... - [0] > $ dir
add-on  codecov.yml documentation  eggshell.c  LICENSE  Makefile        README.md  switch.sh      val.log
ci  createfile.txt  eggshell       eggshell.h  main.c   Makefile-Clang  src        testinput.txt
< Executing script... - [0] > $ ls
add-on  codecov.yml documentation  eggshell.c  LICENSE  Makefile        README.md  switch.sh      val.log
ci  createfile.txt  eggshell       eggshell.h  main.c   Makefile-Clang  src        testinput.txt
< Executing script... - [0] > $ dir
add-on  codecov.yml documentation  eggshell.c  LICENSE  Makefile        README.md  switch.sh      val.log
ci  createfile.txt  eggshell       eggshell.h  main.c   Makefile-Clang  src        testinput.txt
< Executing script... - [0] > $ onetimesoneistwo
execve: No such file or directory
< Executing script... - [0] > $ ls
add-on  codecov.yml documentation  eggshell.c  LICENSE  Makefile        README.md  switch.sh      val.log
ci  createfile.txt  eggshell       eggshell.h  main.c   Makefile-Clang  src        testinput.txt
< Executing script... - [0] > $ dir
add-on  codecov.yml documentation  eggshell.c  LICENSE  Makefile        README.md  switch.sh      val.log
ci  createfile.txt  eggshell       eggshell.h  main.c   Makefile-Clang  src        testinput.txt
< Executing script... - [0] > $ ls
add-on  codecov.yml documentation  eggshell.c  LICENSE  Makefile        README.md  switch.sh      val.log
ci  createfile.txt  eggshell       eggshell.h  main.c   Makefile-Clang  src        testinput.txt
< Executing script... - [0] > $ dir
add-on  codecov.yml documentation  eggshell.c  LICENSE  Makefile        README.md  switch.sh      val.log
ci  createfile.txt  eggshell       eggshell.h  main.c   Makefile-Clang  src        testinput.txt

令人惊讶的是，这不是一个无限循环！当然每个命令onetimesoneistwo运行 4 次后，onetimesoneistwo本身运行两次，但至少它是一些东西。

我猜想execve失败会导致分叉的孩子永远不会终止，但是为什么会exit导致无限循环而exit之后没有重复的所有指令呢？

有趣的故事是，如果我正常运行程序，自己提供输入而不是从文件中获取输入，则不会发生同样的事情，所以我的猜测是我的源函数或我的 fork-exec 出现了严重错误代码。

标签： cforkfgetsexecve

c - execve 失败 - 忽略退出语句

问题描述

解决方案

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