minishell malloc error with EXC_BAD_ACCESS - c

Question

Hi I've recently started learning unix system programming.
I'm trying to create a minishell in c but when I run my code,
I always get:
EXC_BAD_ACCESS (code=EXC_I386_GPFLT
Don't really know what's wrong here. Searched online they say it's something wrong with malloc, but I don't see what's wrong.
Can someone help me with this problem?
#include <stdlib.h>
#include <fcntl.h>
#include <stdio.h>
#include <sys/types.h>
#include <sys/wait.h>
#include <string.h>
#include <unistd.h>
#include "minishell.h"
char promptString[] = "mysh>";
struct command_t command;
int enviromentlength;
int commandlength;
char *pathv[MAX_PATHS];
//to display the prompt in the front of every line
void printPrompt()
{
printf("%s", promptString);
}
//get the user's command
void readCommand(char *buffer)
{
gets(buffer);
}
//get the environment variable and store in a pathEnvVar
int parsePath( char* dirs[] )
{
char* pathEnvVar;
char* thePath;
int i;
for(i = 0; i < MAX_ARGS; i++)
{
dirs[i] = NULL;
}
i = 0;
//use system call to get the environment variable
pathEnvVar = (char*) getenv("PATH");
//printf("%s\n", pathEnvVar);
thePath = (char*) malloc(strlen(pathEnvVar) + 1);
strcpy(thePath, pathEnvVar);
//splict the variable and store in the pathv
char *temp = strtok(thePath, ":");
dirs[i] = temp;
while(temp != NULL)
{
i++;
temp = strtok(NULL, ":");
if(temp == NULL)
{
break;
}
else
{
dirs[i] = temp;
}
}
dirs[i+1] = NULL;
return i;
}
//get the user's command and parameters
int parseCommand(char * commandline)
{
int i = 0;
char* temp;
temp = strtok(commandline, " ");
while(temp != NULL)
{
command.argv[i] = temp;
i++;
temp = strtok(NULL, " ");
}
command.argv[i] = NULL;
return i;
}
//input the user's command to
//fix the absolute path of the command
char* lookupPath(char* dir[], char* command[])
{
char* result = NULL;
int i;
//printf("%c\n", *command.argv[0]);
//if the command is already an absolute path
if(*command[0] == '/')
{
result = command[0];
//printf("test\n");
if( access(result, X_OK) == 0)
{
return result;
}
else
{
fprintf(stderr, "%s: command not found\n", result);
return NULL;
}
}
//if the command is not an absolute path
else
{
for(i = 0; i < enviromentlength; i++)
{
char *temp = (char *) malloc (30);
strcpy(temp, dir[i]);
strcat(temp, "/");
strcat(temp, command[0]);
result = temp;
if( access(result, X_OK) == 0)
{
return result;
}
}
fprintf(stderr, "%s: command not found\n", result);
return NULL;
}
}
//to change the directory and
//display the absolute path of the current directory
void do_cd(char* dir[])
{
char currentdirectory[MAX_PATHS];
if(dir[1] == NULL || (strcmp(dir[1], ".") == 0))
{
printf("director does not change\n");
//printf("The current directory is:%s", currentdirectory);
}
else
{
if(chdir(dir[1]) < 0)
{
printf("change director error\n");
}
else
{
printf("change director success\n");
}
}
getcwd(currentdirectory, MAX_PATHS);
printf("The current directory is:%s\n", currentdirectory);
}
//redirection the result to file
void redirection(char* command, char* commandcontent[], int position, pid_t thisChPID)
{
char* content[commandlength - 1];
char* filename = (char *) malloc(MAX_PATH_LEN);
FILE* fid;
int i = 0;
int stat;
strcpy(filename, commandcontent[position + 1]);
//printf("%s\n", commandcontent[position + 1]);
for(i = 0; i < position; i++)
{
content[i] = commandcontent[i];
//printf("content: %s\n", content[i]);
}
content[i + 1] = NULL;
for(i = 0; i< position + 1; i++)
{
printf("%s\n", content[i]);
}
printf("%s\n", command);
if((thisChPID=fork()) < 0)
{
fprintf(stderr, "fork failed\n");
}
else if(thisChPID == 0)
{
fid = open(filename, O_WRONLY || O_CREAT);
close(1);
dup(fid);
close(fid);
execve(command, content, pathv);
}
else
{
wait(&stat);
}
}
//use pipe to run the program
void piperun(char* command, char* commandcontent[], int position, pid_t thisChPID)
{
printf("%s\n%d\n", command, position);
char* firstcommand[position+1];
char* secondcommand[commandlength-position];
char* result = (char *) malloc(MAX_PATH_LEN);
pid_t child;
//the pipe name
int pipeID[2];
int j;
for(j = 0; j< position; j++)
{
firstcommand[j] = commandcontent[j];
printf("%s\n", firstcommand[j]);
}
firstcommand[j] = NULL;
printf("length: %d\n", commandlength-position);
for(j = 0; j < (commandlength-position); j++)
{
secondcommand[j] = commandcontent[position + 1 + j];
printf("second:%s\n",secondcommand[j]);
}
//secondcommand[j+1] = NULL;
result = lookupPath(pathv, secondcommand);
//printf("%s\n", secondcommand[0]);
printf("%s\n", result);
//create pipe "pipeID"
if(pipe(pipeID)==-1)
{
printf("Fail to creat pipe.\n");
}
if((thisChPID=fork())==-1)
{
printf("Fail to creat child process.\n");
}
if(thisChPID==0)
{
printf("in the child\n");
close(1);
dup(pipeID[1]);
close(pipeID[0]);
close(pipeID[1]);
if(execve(command, firstcommand, pathv)==-1)
{
printf("Child process can't exec command %s.\n",firstcommand[0]);
}
}
else
{
child = fork();
if((child=fork())==-1)
{
printf("Fail to creat child process.\n");
}
if(child==0)
{
close(0);
dup(pipeID[0]);
close(pipeID[1]);
close(pipeID[0]);
if(execve(result, secondcommand, pathv)==-1)
{
printf("Child process can't exec command %s.\n",secondcommand[0]);
}
}
else
{
wait(NULL);
}
}
}
int main()
{
char commandLine[LINE_LEN];
int child_pid; //child process id
int stat; //used by parent wait
pid_t thisChPID;
char *arg[MAX_ARGS];
//the flag of redirection, piping and background running
int redirectionsituation = 0;
int pipesituation = 0;
int background = 0;
char * tempchar;
//Command initialization
int i;
for(i = 0; i < MAX_ARGS; i++ )
{
command.argv[i] = (char *) malloc(MAX_ARG_LEN);
}
//get all directories from PATH env var
enviromentlength = parsePath(pathv);
//Main loop
while(TRUE)
{
redirectionsituation = 0;
pipesituation = 0;
background = 0;
//Read the command line
printPrompt();
readCommand(commandLine);
//input nothing
if(commandLine[0] == '\0')
{
continue;
}
//quit the shell?
if((strcmp(commandLine, "exit") == 0) || (strcmp(commandLine, "quit") == 0))
{
break;
}
//if it is background running
if(commandLine[strlen(commandLine) - 1] == '&')
{
printf("backgrond\n");
tempchar = strtok (commandLine, "&");
//strcpy(commandLine, tempchar);
printf("%s\n", tempchar);
background = 1;
}
//Parse the command line
commandlength = parseCommand(commandLine);
//if the command is "cd"
if(strcmp(command.argv[0], "cd") == 0)
{
do_cd(command.argv);
continue;
}
//Get the full path name
command.name = lookupPath(pathv, command.argv);
printf("command name %s\n", command.name);
//report error
if( command.name == NULL)
{
continue; //non-fatal
}
//if redirection is required
for(i = 0; i < commandlength; i++)
{
if(strcmp(command.argv[i], ">") == 0)
{
redirectionsituation = 1;
break;
}
}
if(redirectionsituation == 1)
{
redirection(command.name, command.argv, i, thisChPID);
continue;
}
//if pipe is required
for(i = 0; i < commandlength; i++)
{
if(strcmp(command.argv[i], "|") == 0)
{
pipesituation = 1;
break;
}
}
if(pipesituation == 1)
{ //run pipe
piperun(command.name, command.argv, i, thisChPID);
continue;
}
//normal running
if((thisChPID=fork()) < 0)
{
fprintf(stderr, "fork failed\n");
}
else if(thisChPID == 0)
{
//printf("run again\n");
execve(command.name, command.argv, pathv);
}
else
{
//do not put the process in the background, wait until the child process terminates
if(background == 0)
{
wait(&stat);
}
}
}
return 0;
}

Answer 1

Run it in a debugger and see where you are dereferencing a null.