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我正在写一个小壳来学习C.现在我想执行自定义命令，但它不工作。我的execvp用法有什么问题？
$ ./a.out
OS>ls
10357: executing ls
failed to execute ls
: (2: No such file or directory)
我不能使用系统调用来执行自定义命令，我应该使用execvp和fork。但为什么它现在工作？整个代码
#include<sys/stat.h>
#include <stdio.h>
#include <unistd.h>
#include <string.h>
#include <dirent.h>
#include <errno.h>
#include <stdarg.h>
#include <stdlib.h>
#include <signal.h>
int mystrcmp(char const *, char const *);
struct command
{
char * const *argv;
};
static _Noreturn void err_syserr(char *fmt, ...)
{
int errnum = errno;
va_list args;
va_start(args, fmt);
vfprintf(stderr, fmt, args);
va_end(args);
if (errnum != 0)
fprintf(stderr, "(%d: %s)\n", errnum, strerror(errnum));
exit(EXIT_FAILURE);
}
/* Helper function that spawns processes */
static int spawn_proc(int in, int out, struct command *cmd)
{
pid_t pid;
if ((pid = fork()) == 0)
{
if (in != 0)
{
if (dup2(in, 0) < 0)
err_syserr("dup2() failed on stdin for %s: ", cmd->argv[0]);
;
close(in);
}
if (out != 1)
{
if (dup2(out, 1) < 0)
err_syserr("dup2() failed on stdout for %s: ", cmd->argv[0]);
close(out);
}
fprintf(stderr, "%d: executing %s\n", (int)getpid(), cmd->argv[0]);
execvp(cmd->argv[0], cmd->argv);
err_syserr("failed to execute %s: ", cmd->argv[0]);
}
else if (pid < 0) {
err_syserr("fork failed: ");
}
return pid;
}
/* Helper function that forks pipes */
static void fork_pipes(int n, struct command *cmd)
{
int i;
int in = 0;
int fd[2];
for (i = 0; i < n - 1; ++i)
{
pipe(fd);
spawn_proc(in, fd[1], cmd + i);
close(fd[1]);
in = fd[0];
}
if (dup2(in, 0) < 0) {
err_syserr("dup2() failed on stdin for %s: ", cmd[i].argv[0]);
}
fprintf(stderr, "%d: executing %s\n", (int)getpid(), cmd[i].argv[0]);
execvp(cmd[i].argv[0], cmd[i].argv);
err_syserr("failed to execute %s: ", cmd[i].argv[0]);
}
#define BUFFERSIZE 200
int main() {
char *args[80];
char buffer[BUFFERSIZE];
char *prompt = "OS";
char *a = ">";
char *tok;
tok = strtok (buffer," ");
while(buffer != NULL) {
bzero(buffer, BUFFERSIZE);
printf("%s%s",prompt,a);
fgets(buffer, BUFFERSIZE, stdin);
if(mystrcmp(buffer,"cd") == 0) {
tok = strchr(buffer,' ')+1; //use something more powerful
*strchr(tok, '\n')='\0';
cd(tok);
}
else if(mystrcmp(buffer,"exit") == 0) {
return 0;
}
else {
//system("ls"); //for testing the CWD/PWD
char *commandbuffer[] = { buffer, 0 };
//char *less[] = { "less", 0 };
struct command cmd[] = { {commandbuffer} };
fork_pipes(1, cmd);
printf("Spawned foreground process: %d\n", getpid());
}
}
return 0;
}
int mystrcmp(char const *p, char const *q)
{
int i = 0;
for(i = 0; q[i]; i++)
{
if(p[i] != q[i])
return -1;
}
return 0;
}
int cd(char *pth) {
char path[BUFFERSIZE];
strcpy(path,pth);
char *token;
char cwd[BUFFERSIZE];
if(pth[0] != '/')
{ // true for the dir in cwd
getcwd(cwd,sizeof(cwd));
strcat(cwd,"/");
strcat(cwd,path);
chdir(cwd);
} else { //true for dir w.r.t./
chdir(pth);
}
printf("Spawned foreground process: %d\n", getpid());
return 0;
}