[英]Execvp works with "ls -l | wc" and failed with "ls -l|wc
我正在编写一个 shell,目前正在实现管道进程。 我可以运行"ls -l | wc"
,但是当运行"ls -l|wc"
,进程失败。
我试过用 gdb 调试,但无法做任何事情,因为它们看起来都等于相同的值(在解析后)。
运行ls -l | wc
ls -l | wc
并在parseCmdWithPipe
函数上设置断点并打印出我得到的当地人:
argOne = {0x7fffffffdad0 "ls", 0x7fffffffdad3 "-l", 0x0}
argTwo = {0x7fffffffdad8 "wc", 0x0}
当运行ls -l|wc
并在parseCmdWithPipe
函数上有一个断点并打印出当地人时,我得到:
argOne = {0x7fffffffd9b0 "ls", 0x7fffffffd9b3 "-l", 0x0}
argTwo = {0x7fffffffd9b8 "wc", 0x0}
我用来解析和使用execvp
的代码(第二个函数)
/* parse user input from fget */
int parseLine(char *line, char **argv) {
line[strlen(line) - 1] = '\0';
//This section tries to figure out if we have the case
//"ls -l|wc", if it does it makes a new string of "ls -l | wc"
int cmdType = 1;
int size = sizeof(line);
char tempLine[size + 3];
bool pipeSeen = false;
for (int i = 0; i < size; i++) {
if (line[i] == '|' && line[i - 1] != ' ') {
tempLine[i] = ' ';
tempLine[i + 1] = '|';
tempLine[i + 2] = ' ';
pipeSeen = true;
} else {
if (pipeSeen == true)
tempLine[i + 2] = line[i];
else
tempLine[i] = line[i];
}
}
if (pipeSeen == true) {
tempLine[size + 2] = '\0';
line = tempLine; // change "ls -l|ls to ls -l | wc"
}
/* parse line and store it in argv */
while (*line) {
while (*line == ' ')
*line++ = '\0';
//Figure out what type of command we may have
if (*line == '<')
cmdType = (cmdType == 3) ? 5 : 2;
else if (*line == '>' )
cmdType = (cmdType == 2) ? 5 : 3;
else if (*line == '|')
cmdType = 4;
*argv++ = line;
while (*line != '\0' && *line != ' ' && *line != '\t' && *line != '\n')
line++;
}
*argv = '\0';
return cmdType;
}
void parseCmdWithPipe(char **argv) {
int size = getCmdSize(argv);
char val[1];
int pipePosition = 0;
for (int i = 0; i < size; i++) {
strcpy(val, argv[i]);
if (val[0] == '|') {
pipePosition = i;
break;
}
}
char *argOne[pipePosition + 1];
for (int i = 0; i < pipePosition; i++) {
argOne[i] = argv[i];
}
argOne[pipePosition] = '\0';
char *argTwo[size - pipePosition];
for (int i = 0; i < (size - pipePosition); i++) {
argTwo[i] = argv[i + pipePosition + 1];
}
argTwo[size - pipePosition - 1] = '\0';
int pfd[2], pid;
if (pipe(pfd) == 1)
syserror("Could Not create a pipe");
switch (pid = fork()) {
case -1:
syserror( "Fork Failed" );
case 0:
if (dup2(pfd[0], 0) == -1|| close (pfd[0]) == -1 || close (pfd[1]) == -1)
syserror("Failed to run dup2 or close pfd in second child");
execvp(argTwo[0], argTwo);
syserror("execvp unsuccessful in 2nd child");
}
....
我希望"ls -l|wc"
给我相同的结果"ls -l | wc"
给我的是
11 92 597
但实际输出是
execvp unsuccessful in 2nd child
(No such file or directory)
主要问题是int size = sizeof(line);
它不计算line
指向的字符串的大小和长度,而只是计算char *
的大小。
你应该写int size = strlen(line);
并且可能不会将此变量称为size
,而是len
。
代码太复杂,你不应该尝试在|
周围插入空格|
顺便说一下,你没有对<
和>
做同样的事情。
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