runcommand(( 用于通过fork()在 shell 中执行命令。
对于在后台启动的命令，如何打印有关命令终止的信息(使用 waitpid 的 WNOHANG 选项(？
打印信息：进程终止 [PID]
所有子进程完全结束非常重要
#include <sys/types.h>
#include <signal.h>
#include <fcntl.h> // tipi di apertura file
#include <assert.h> // assert
#include <string.h>
#include <unistd.h>
#include <stdio.h>
#include <stdlib.h>
#include <sys/types.h>
#include <sys/wait.h>
#define EOL 1 /* end of line */
#define ARG 2 /* normal topic */
#define AMPERSAND 3 /* & */
#define SEMICOLON 4 /* ; */
#define REDIRECT 5 /* > */
#define APPEND 6 /* >> */
#define MAXARG 512 /* maximum number of arguments */
#define MAXBUF 512
#define FOREGROUND 0
#define BACKGROUND 1
int gettok(char **outptr); /* reads a symbol */
void runcommand(char **cline,int where); /* execute a command */
int inarg(char c); /* check if c is not a special character */
pid_t pid;
char prompt[MAXBUF];
static char inpbuf[MAXBUF], tokbuf[2*MAXBUF], *ptr, *tok;
static char special[]=
{' ', 't', '&', ';', 'n', ' ', '>'};
int proc(void) /* treats a line of input */
{
char *arg[MAXARG+1]; /* array of pointers for runcommand */
int toktype;
int n_arg; /* number of topics considered so far */
int type; /* FOREGROUND o BACKGROUND */
n_arg=0;
while (1)
{
switch (toktype = gettok(&arg[n_arg]))
{
/* if argument: go to the next symbol */
case ARG:
if (n_arg < MAXARG)
{n_arg++;}
break;
/* if end of line or ';' or '&' executes the command now contained in arg, putting NULL to signal the end of the arguments: it serves as execvp */
case EOL:
case SEMICOLON:
case AMPERSAND:
type = (toktype == AMPERSAND) ? BACKGROUND : FOREGROUND;
if (n_arg != 0)
{
arg[n_arg] = NULL;
runcommand(arg,type);
}
if (toktype == EOL) return 1;
n_arg = 0;
break;
}
}
}
void runcommand(char **command,int wr)
{
int exitstat,ret;
pid = fork();
if (pid == (pid_t) -1)
{
perror("smallsh: fork fallita");
return;
}
if (pid == (pid_t) 0) /* child */
{
execvp(*command,command);/* executes a command */
perror(*command);
exit(1);
}
else if(wr != BACKGROUND) /* father */
{
ret = waitpid(pid, &exitstat, 0);
if (ret == -1) perror("wait");
}
}
int scan(char *p); /* print the prompt and read a line */
int main()
{
while(scan(prompt) != EOF)
proc();
}
int scan(char *p)
{
int c, count;
ptr = inpbuf;
tok = tokbuf;
printf("%s ",p);
count=0;
while(1)
{
if ((c = getchar()) == EOF)
return(EOF);
if (count < MAXBUF)
inpbuf[count++] = c;
if (c == 'n' && count < MAXBUF)
{
inpbuf[count] = ' ';
return(count);
}
if (c == 'n')
{
printf("riga in input troppo lungan");
count = 0;
printf("%s ",p);
}
}
}
int gettok(char **outptr)
{
int type;
*outptr = tok;
while (*ptr == ' ' || *ptr == 't') ptr++;
*tok++ = *ptr;
switch(*ptr++)
{
case 'n':
type = EOL; break;
case '&':
type = AMPERSAND; break;
case ';':
type = SEMICOLON; break;
default:
type = ARG;
while(inarg(*ptr))
*tok++ = *ptr++;
}
*tok++ = ' ';
return(type);
}
int inarg(char c)
{
char *wrk;
for (wrk = special; *wrk != ' '; wrk++)
if (c == *wrk) return(0);
return(1);
}
因此，如果您调用ret = waitpid(pid, &exitstat, WNOHANG)，那么即使孩子没有退出，该命令也会返回。因此，您需要查看返回值ret以查看函数是否成功，然后查看exitstat的值以查看子值是否已退出(通过从main()函数返回或由于信号(：
if(ret >= 0)
{
if(WIFEXITED(exitstat) || WIFSIGNALED(exitstat))
{
printf("Child endedn");
}
}
else
{
printf("Error!n");
}
注意：
在某些情况下，您可能还需要检查
WIFSTOPPED(exitstat)。详见 waitpid(2(。如果出现错误，您可以检查 errno 以获取有关出错的更多信息。