我在C中创建了一个shell，这里是代码。我也对代码进行了评论。
#include <stdio.h>
#include <stdlib.h>
#include <string.h>
#include <sys/wait.h>
#include <sys/types.h>
#include <unistd.h>
#include <signal.h>
#define PATH "path=" //just a constant string
#define DELIM ":" //just a constant string
typedef void (*sighandler_t)(int);
char* cwdtemp = "";
int false=0;
/*structure of functions*/
char* readLine(char* line, size_t len);
void split(char* input, char *argv[]);
int checkpipe( char *input);
void run (char* argv[]);
void runPipe(char *argv[], char *argv2[]);
void setPath(char* inputLine);
char* getPath();
void changedir(char* dir);
char* strcasestr(const char *haystack, const char *needle);
void handle_signal(int signo);
int main(){
char* input=NULL; //string to save user input
char* input2; //string to save the 2nd command if theres a pipe
char *argv[50]; //array to sabe the user input after spliting by spaces
char *argv2[30]; //array to save the second command if thrs a pipe
char argv3[100]; //array for the use of getcwd function
int i; //varibale to save the index of the pipe
char* cwd; //variable to save the current working directory
while (1) { //infinite while loop
signal(SIGINT, SIG_IGN); //capture teh signal and ignore its default action
signal(SIGINT, handle_signal); //capture the signal and parse it to handle signal function
cwd=getcwd(argv3,100); // get the current working directory and save it to cwd
cwdtemp=cwd; //save current directory as string to cwdtemp
printf("%s",cwd); //print cwd
printf(":~mosh:~$ "); //show a prompt
input=readLine(input, 0); //read the user input and save it as a string(char array)
if(strcasestr(input, PATH) == input){ //strcasesrt function will check user input and see if it has "path="(substring matching)
setPath(input); //pass user input to setpath function
}else{
i=checkpipe(input); //saves the index of the ' | ' charactor in user input string
if(i==0){ //if theres no pipe
split(input, argv); //split the user input by spaces and save them in argv array
if(argv[0] == NULL) { //if user input is null continue the loop
continue;
}
/* exit this shell when "exit" is inputed */
if(strcmp(argv[0], "exit") == 0) {
exit(0);
}
if(strcmp(argv[0], "cd") == 0) { //if the user entered cd command(its not found in /bin)
changedir(argv[1]); //pass the name of the directory that should be changed to the changedir function
}
run(argv); //pass argv array to run function
/*checks if the command is valid*/
if(false==-1 ){
if(strcmp(argv[0], "exit") == 0){}
else if(strcmp(argv[0], "cd") == 0){}
else{
printf("no such mosh command\n");}
false=0;
}
}
else{ //if thers a pipe
input2=&input[i+1]; //points input2 to the memory location of the charactor after charactor '|'
input[i]='\0'; //adds the escape charatctor to the charactor before '|' charactor of the input and signal the end of input string
split(input, argv); //split input by spaces and save in argv array
split(input2, argv2); //split input2 by spaces and save in argv2 array
if(fork()){ //creates a child process
wait(NULL); //wait till the child process terminates
}
else{ //else execute the pipe in parent process
runPipe(argv, argv2);
}
}
}
}
}
/*split the input by space and fill to the given array*/
void split(char* input, char *argv[]){
char* p; //char array
int argc;
argc=0;
p=strtok(input, " "); //torkanize user input by spaces and save to p
while(p!=NULL){ //until thrs charactors in p
argv[argc]=p;
argc++;
p=strtok(NULL, " "); //points the torkanizer to the point where it stoped before and torkanize p
}
argv[argc]='\0'; //adds end of string to the last index of argv
}
/* read a line */
char* readLine(char* line, size_t len){
getline(&line, &len, stdin);
*(line+strlen(line)-1)='\0';
return line;
}
/*return the array index of | character if any, otherwise 0*/
int checkpipe( char *input){
int i = 0;
int returnvalue = 0;
for ( ; i < strlen ( input ) ; i++ ){
if ( input[i] == '|' ){ //find the index where '|' in userinput and retuen the index ,if not found return 0
returnvalue = i;
break;
}
}
return returnvalue;
}
/*execute a command without | in another process*/
void run (char* argv[]){
pid_t pid = fork(); //creats a fork and save its pid in pid variable
if(pid == -1) {
perror("fork");
exit(1);
} else if(pid == 0) { //if child process was created successfully
false=execvp(argv[0], argv); //execute the command by execcvp function
//exit(0);
} else {
wait(NULL); //wait till child process terminates
}
}
/*execute a command with a | in two processes*/
void runPipe(char *argv[], char *argv2[]){
int pfds[2]; //int array to be used in file descriptors
pipe(pfds); //creates the pipe
int stdin_bak = dup(0);
if (fork()==0) { //if the creation of fork successfull
close(1); //close current stdout
dup(pfds[1]); //duplicate stdout to the write end of the pipe
close(pfds[0]); //close stdin
printf("i'm child\n");
execvp(argv[0], argv); //execute teh command
exit(0);
} else { //else in parent
close(0); //close current stdin
dup(pfds[0]); //duplicate stdin to the read end of the pipe
close(pfds[1]); //close stdout
wait(NULL); //wait till child process terminates
execvp(argv2[0], argv2);//execute command
}
}
/*add a given path to the environmental variable PATH*/
void setPath(char* inputLine){
char* pathIn = &inputLine[strlen(PATH)]; //save the input path that was given by user(without path=)
char* oldPath = getenv("PATH"); //get the current path from getenv function and save to oldpath
int lenPath = strlen(oldPath) + strlen(pathIn) + 1 + 1;
char* pathOut = malloc(sizeof(char) * lenPath); //allocate memoery to pathout by malloc
strcat(pathOut, oldPath); //combine oldpath and pathout and save to pathout by strcat function
strcat(pathOut, DELIM); //combine oldpath and DELIM(constant string) and save to pathout
strcat(pathOut, pathIn); //combine oldpath and pathinand save to pathout
pathOut[lenPath - 1] = '\0';
setenv("PATH", pathOut, 1); //set the new path by setenv function
free(pathOut); //free the memory allocated by malloc
}
/*change directory if possible*/
void changedir(char* dir){
if(dir=='\0'){ //if user entered nothing after cd
chdir( "/home/" ); //change to home
}else{
if(chdir(dir)==-1){ //if chdir function returned error
printf("%s:Cannot find the directory\n",dir);
}
}
}
void handle_signal(int signo)
{
printf("\n");
printf("%s",cwdtemp);
printf(":~mosh:~$ ");
fflush(stdout); //flush the stdout or printf will be in sameline
}
这是我的问题。 编译完这段代码后，我给出了一个像“hdgdg”这样的命令，这是一个错误的命令。所以输出是“找不到命令”。但是当我运行像“hakka | akjk”这样的命令（这是一个管道命令）时，我输出有一个无限循环。所以我该如何解决这个问题呢？ 谢谢。