Shell-like program C - c

Question

The code below is supposed to work as a shell. It has the previous and next option, a history like feature, the exit and the execute command.
#include <stdio.h>
#include <stdlib.h>
#include <string.h>
#include <unistd.h>
#define BUFFER_SIZE 256
#define HISTORY_LENGTH 128
int executeCommand(char*cmd)
{
return(!strcmp(cmd,"e\n"));
}
int exitCommand(char*cmd)
{
return (!strcmp(cmd,"exit\n"));
}
int previousCommand(char*cmd)
{
return (!strcmp(cmd,"p\n"));
}
int nextCommand(char*cmd)
{
return (!strcmp(cmd,"n\n"));
}
void execute(char *line)
{
line[strlen(line)-1]='\0';
char **arguments;
char* temp;
int i=0;
arguments=(char**)malloc(sizeof(char)*10);
temp=strtok(line," ");
arguments[i]=malloc(strlen(temp)*sizeof(char));
if(arguments[i]!=NULL)
{
strcpy(arguments[i],temp);
i++;
}
else
{
printf("Out of memory");
}
while(temp!=NULL)
{
temp=strtok(NULL," ");
if(temp==NULL){
arguments[i]=NULL;
}
else{
arguments[i]=malloc(strlen(temp)*sizeof(char));
if(arguments[i]!=NULL)
{
strcpy(arguments[i],temp);
i++;
}
}
}
printf("%s ",arguments[0]);
printf("%s ",arguments[1]);
printf("%s ",arguments[2]);
execvp(arguments[0],arguments);
}
int main(int argc, char*argV[]) {
int i;
char *cmd=(char*)malloc(sizeof(char)*BUFFER_SIZE);
char **history=NULL;
int historylength=0;
int currentCommand=0;
history=(char**)malloc(sizeof(char)*BUFFER_SIZE);
do{
fgets(cmd,BUFFER_SIZE-1,stdin);
if(exitCommand(cmd))
break;
else
if(previousCommand(cmd))
{
if(currentCommand>0)
printf("%s",history[--currentCommand]);
else if(currentCommand==0)
{
currentCommand=historylength;
printf("%s",history[--currentCommand]);
}
}
else
if(nextCommand(cmd))
{
if(currentCommand<historylength)
printf("%s",history[currentCommand++]);
}
else
if(executeCommand(cmd))
{
execute(history[--currentCommand]);
}
else
{
history[historylength]=malloc(strlen(cmd)*sizeof(char));
if(history[historylength]!=NULL)
{
strcpy(history[historylength],cmd);
currentCommand=++historylength;
}
else
{
printf("Out of memory");
break;
}
}
} while(1);
free(cmd);
for(i=0;i<historylength;i++)
free(history[i]);
free(history);
return 0;
}
I want to make this work for the function cat. I type in the e cat main.c and I expect it to execute the cat command but it's not doing anything, what am I doing wrong here? I'm not a pro at this so I appreciate all the help.

Answer 1

This is incorrect:
arguments=(char**)malloc(sizeof(char)*10);
as arguments is a char**, so the code needs to allocate sizeof(char*). Change to:
arguments = malloc(10 * sizeof(*arguments));
Same mistake for history also. Additionally, see Do I cast the result of malloc?
There is one char less than required being allocated for the char* as strcpy() writes a terminating null character. Change:
arguments[i]=malloc(strlen(temp)*sizeof(char));
to:
arguments[i] = malloc(strlen(temp) + 1);
sizeof(char) is guaranteed to be 1 and can be omitted from the size calculation.
Prevent i from exceeding the bounds of the memory allocated for arguments. As the code currently stands there is no protection to prevent i from exceeding 9 (0 to 9 are the valid values for i as arguments was allocated 10 elements).