我正在为大学作业制作一个迷你外壳。我们必须读入命令，从路径 var 中找到要执行的二进制文件，然后执行命令，无论有无管道。除了管道，我的一切都正常工作（我认为）。通过网络搜索，我已经能够构建一个测试程序，该程序使用两个硬编码命令并将一个管道连接到另一个，并获得预期的结果。现在，当我将该代码复制并粘贴到我的实际程序中时，第一个命令输出正常（实际上输出命令就像没有管道一样），而第二个我认为实际上没有做任何事情（第一个命令的输出不是通过管道传递到第二个）。
这是整个代码：
#include <stdio.h>
#include <unistd.h>
#include <string.h>
#include <stdlib.h>
#define BUFFSIZE 1024
#define MAXWORDS 17
#define MAXCHAR 64
static char *path;
extern char **environ;
//split cmd "string" on pipe (|) symbol
void split(char **pipe, char **left, char **right, int n)
{
int i, x;
for(i = 0; i < n; i++)
{
if (strchr(&pipe[i][0], '|') != 0)
{
for(x = 0; x < i; x++)
strcpy(left[x], pipe[x]);
left[x++] = 0;
break;
}
}
i++;
for(x = 0; i < n; x++)
strcpy(right[x], pipe[i++]);
right[x++] = 0;
}
//Find directory where cmd can be executed from (PATH or direct access)
char *finddir(char *s)
{
char *pp;
char *pf;
int ok;
strcpy(path, getenv("PATH"));
pp = strtok(path, ":");
while (pp != NULL)
{
pf = (char *)malloc(strlen(pp) + strlen(s) + 2);
if (pf == NULL)
{
fprintf(stderr, "Out of memory in finddir\n");
return NULL;
}
strcpy(pf,pp);
strcat(pf,"/");
strcat(pf,s);
ok = !access(pf, X_OK);
free(pf);
if (ok)
return pp;
pp = strtok(NULL, ":");
}
return NULL;
}
int cmdcheck(char *cmd, char *p)
{
char *dir;
if (strchr(p, '/') != NULL)
sprintf(cmd, "%s\0", p);
else
{
dir = finddir(p);
if (dir == NULL)
return 1;
else
sprintf(cmd, "%s/%s\0", dir, p);
}
return 0;
}
void runpipe(int pfd[], char *cmd1, char *p1[], char *cmd2, char *p2[])
{
int pid;
int status;
switch (pid = fork())
{
case 0: //Child
dup(pfd[0]);
close(pfd[1]); //the child does not need this end of the pipe
execve(cmd2, p2, environ);
perror(cmd2);
default: //Parent
dup(pfd[1]);
close(pfd[0]); //the parent does not need this end of the pipe
execve(cmd1, p1, environ);
perror(cmd1);
case -1: //ERROR
perror("fork-RP");
exit(1);
}
}
int main(void)
{
int status; //read status when reading cmd in
char ch; //character currently reading
int n, i, x; //(n) count of chars read; (i) cmd args iter; (x) cmd arg iter in cmd array
char buffer[BUFFSIZE]; //read buffer
char *token; //token var when splitting buffer
int pid0, pid1, pid2; //return ID from fork call
int which; //return value from wait (child pID that just ended)
char msg[100]; //messages to print out
char *cmd1, *cmd2; //cmds when piping
char *params[MAXWORDS]; //cmd parameters to send to execve
int fd[2]; //pipe file descriptors
char *pparam1[MAXWORDS]; //cmd "string" on left side of pipe
char *pparam2[MAXWORDS]; //cmd on right side of pipe
for(;;)
{
for (i = 0; i < MAXWORDS; i++)
params[i] = malloc(MAXCHAR);
n = 0;
write(1, "# ", 2);
for(;;)
{
status = read(0, &ch, 1);
if (status == 0)
return 0; //End of file
if (status == -1)
return 1; //Error
if(n == BUFFSIZE)
{
write(1, "Line too long\n", 14);
return 1;
}
buffer[n++] = ch;
if(ch == '\n')
break;
}
buffer[n] = '\0';
x = 0;
token = strtok(buffer, " \t\n\0");
while(token != NULL)
{
strcpy(params[x++], token);
token = strtok(NULL, " \t\n\0");
}
params[x] = 0;
path = getenv("PATH");
if (path == NULL)
{
fprintf(stderr, "PATH environment variable not found.\n");
return 1;
}
n = strlen(path);
path = (char *)malloc(n+1);
if (path == NULL)
{
fprintf(stderr, "Unable to allocate space for copy of PATH.\n");
return 1;
}
cmd1 = malloc(MAXCHAR);
cmd2 = malloc(MAXCHAR);
for (i = 0; i < MAXWORDS; i++)
pparam1[i] = malloc(MAXCHAR);
for (i = 0; i < MAXWORDS; i++)
pparam2[i] = malloc(MAXCHAR);
split(params, pparam1, pparam2, x);
//Check first cmd
if(cmdcheck(cmd1, pparam1[0]))
{
sprintf(msg, "cmd '%s' is not executable\n", pparam1[0]);
write(1, msg, strlen(msg));
break;
}
//Check second cmd
if(cmdcheck(cmd2, pparam2[0]))
{
sprintf(msg, "cmd '%s' is not executable\n", pparam2[0]);
write(1, msg, strlen(msg));
break;
}
pipe(fd);
switch (pid0 = fork())
{
case 0: //Child
switch (pid1 = fork())
{
case 0: //Child
runpipe(fd, cmd1, pparam1, cmd2, pparam2);
exit(0);
default:
exit(0);
//break;
case -1: //ERROR
perror("fork-2");
exit(1);
}
default: //Parent
which = wait(&status);
if (which == -1)
{
write(1, "wait failed\n", 12);
exit(1);
}
if (status & 0xff)
sprintf(msg, "process %d terminated abnormally for reason %d\n", which, status & 0xff);
else
sprintf(msg, "process %d terminated normally with status %d\n", which, (status >> 8) & 0xff);
write(1, msg, strlen(msg));
break;
case -1: //ERROR
perror("fork-1");
exit(1);
}
free(cmd1);
free(cmd2);
for (i = 0; i < MAXWORDS; i++)
free(pparam1[i]);
for (i = 0; i < MAXWORDS; i++)
free(pparam2[i]);
free(path);
for (i = 0; i < MAXWORDS; i++)
free(params[i]);
}
return 0;
}
打字回声一| 提示符处的wc -l将仅输出一个带有相应等待打印语句的语句。自从我使用 C 以来已经有几年了，所以我走在正确的轨道上吗？
谢谢。
编辑：这是现在的运行管道功能。但唯一打印的是等待语句。
void runpipe(int pfd[], char *cmd1, char *p1[], char *cmd2, char *p2[])
{
const int READ = 0;
const int WRITE = 1;
int pid;
int status;
switch (pid = fork())
{
case 0: //Child
close(pfd[WRITE]);
dup2(pfd[READ], STDIN_FILENO);
close(pfd[READ]);
execve(cmd2, p2, environ);
perror(cmd2);
default: //Parent
close(pfd[READ]);
dup2(pfd[WRITE], STDOUT_FILENO);
close(pfd[WRITE]);
execve(cmd1, p1, environ);
perror(cmd1);
case -1: //ERROR
perror("fork-RP");
exit(1);
}
}