我正在尝试实现我自己的一个非常小的外壳。我必须能够处理管道,比如
ls -l | wc -l
但一次只能用于两个程序。现在,我有这个:
#include <stdio.h>
#include <stdlib.h>
#include <errno.h>
#include <unistd.h>
#include <string.h>
#include <sys/types.h>
#include <sys/wait.h>
#define BUFFER_SIZE 256
#define NO_PARAMS 32
void split_string(char **params, char *string){
char *arg;
int i;
arg = strtok(string, " ");
params[0] = arg;
i = 1;
while(arg != NULL){
arg = strtok(NULL, " ");
params[i] = arg;
i++;
}
}
int main(int argc, char **argv){
char string[BUFFER_SIZE];
char *prog1, *prog2;
int i, err;
int fd[2];
pid_t pid1, pid2;
size_t buffer = BUFFER_SIZE;
char *params1[NO_PARAMS], *params2[NO_PARAMS];
int pipe_exists = 0;
memset(string,0,buffer);
while(1){
/*Read command*/
fgets(string, BUFFER_SIZE-1, stdin);
if(string == NULL){
perror("Error reading input:\n");
exit(1);
}
/*replace linefeed character with end of line character*/
for(i=0;i<BUFFER_SIZE;i++){
if(string[i] == 10){
string[i] = 0;
}
}
/*check if command is "exit"*/
if(strcmp(string,"exit") == 0){
return 0;
}
/*split command into different program calls*/
prog1 = strtok(string, "|");
prog2 = strtok(NULL,"\0");
if(prog2 != NULL){
pipe_exists = 1;
printf("PIPE!\n");
err = pipe(fd);
if(err<0){
perror("Error creating pipe:\n");
exit(1);
}
}
/*split string into arguments*/
split_string(params1, prog1);
if(pipe_exists){
split_string(params2, prog2);
}
/*fork child process*/
pid1 = fork();
if(pid1==0){ /*child 1*/
if(pipe_exists){
close(fd[0]); /*close read-end*/
err = dup2(fd[1], 1);
if(err<0){
perror("Error with dup in child 1!\n");
exit(1);
}
}
execvp(params1[0],params1);
perror("Error calling exec()!\n");
exit(1);
}else{ /*parent*/
if(pipe_exists){
pid2 = fork();
if(pid2==0){ /*child 2*/
close(fd[1]); /*close pipe write-end*/
err = dup2(fd[0], 0);
if(err<0){
perror("Error with dup in child 2!\n");
exit(1);
}
execvp(params2[0],params2);
perror("Error calling exec()!\n");
exit(1);
}else{ /*parent with 2 children*/
waitpid(pid1,0,0);
waitpid(pid2,0,0);
}
}else{ /*parent with 1 child*/
waitpid(pid1,0,0);
}
}
}
}
现在,它可以很好地处理单个命令,但是当我输入类似上面的命令时,什么也没有发生!
谢谢!