Simple shell simulate the linux 'history' command

**ivar5000** · 10-19-2017

I have a simple C shell that recognizes change directory and exit commands. Any other commands are printed as is to the command line. I need to simulate the linux 'history' command using an array of stucts. Can anyone help me get started on this? I'm having trouble with how to do this. I believe I need to malloc size for this but not sure how to and how much to..

Code:

struct cmd{
    char * cmd;
}

This is my simple shell:

Code:

#define MAX_LENGTH 4096
#define DELIMS " \t\r\n"


int main(int argc, char *argv[]) {
  char buffer[MAX_LENGTH];


  while (1) {
    fprintf(stderr, "$");
    
    //Exit if not reading from stdin
    if (!fgets(buffer, MAX_LENGTH, stdin)) {
      break;
    }


    char* token = strtok(buffer, DELIMS); //store each token
    if(token != NULL) {
      //exit
      if(strcmp(token, "exit") == 0) {
        ExitSmash();
      }
      //cd
      else if (strcmp(token, "cd") == 0) {
        char* args = strtok(0, DELIMS);
        ChangeDirectory(args);
      }
      //tokenize & print to command line
      else {
        int i = 0;
        while(token != NULL) {
          printf ("[%d] %s\n",i++, token);
          token = strtok (NULL, DELIMS);
        }  
      }
    }
  }
  return 0;
}

**Salem** · 10-19-2017

So start with
char history [10][BUFSIZ];

**ivar5000** · 10-19-2017

why is history a char array? Shouldn't it be an array of stucts?
Sorry, beginner here, this is all new to me. Just learnt about pointers and structs..

**whiteflags** · 10-19-2017

Originally Posted by ivar5000

why is history a char array? Shouldn't it be an array of stucts?
Sorry, beginner here, this is all new to me. Just learnt about pointers and structs..

Maybe it could be a struct in the future if the program gets more complicated, like when you start using dynamic memory.

For now though, the commands are strings, so you can simply store commands from the past in an array of strings.

Start simple, get it working, and then gradually make it more complex.

**ivar5000** · 10-20-2017

Sorry I wasn't clear earlier. Among other things, this happens to be an excercise on structs & pointers, so I am required to use an array of cmd structs which stores 25 of the last entered commands into history and to have a history.c and history.h with the following functions:

Init_history // Makes sure all buffers (struct array) are initialized and ready to use.
- This is equivalent to a constructor in Java.
add_history // adds command into a cmd struct and append to your history buffer
- This is equivalent to a method in Java.
clear_history // properly fees all memory and clears the history buffer
- This is equivalent to a method in Java. Unlike Java, however, you are responsible for freeing any memory you malloc’ed (there is no garbage collector).
print_history // Prints the history to the command line (See the example above)
- This is similar to a toString in Java, except it is not returning a String, it is just printing.

So here's what I tried,

Code:

...
typedef struct Command_struct{
  char* commandString;
} Command;
...

Command  cmd[25];
int count = 0;

while (1) {
    fprintf(stderr, "$");

    //Exit if not reading from stdin
    if (!fgets(buffer, MAX_LENGTH, stdin)) {
      break;
    }

cmd[count].commandString = buffer;

    char* token = strtok(buffer, DELIMS); //store each token
...
count++;
...

Am I doing this right, or do i need to call init_history first? How do I initialize this?

**Salem** · 10-21-2017

You need a char array (and strcpy) to make an actual copy of the command line.

Otherwise you just end up with 25 pointers to buffer.

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