Thread: Creating a simple shell using C

I am currently in a beginning C/UNIX class and I am having major difficulties with the first assignment we have been given using C. We were given the source code for a simple shell and are supposed to implement a history feature into the code we've been given.

It is supposed to keep a history file that records previous commands preceded by a number (like bash keeps). It is also supposed to be capable of supporting two additional features: when !(number) is typed at command line, it prints the last command that corresponds to that number, and when !(string) is typed at command line it prints the last command that begins with that string.

I am extremely frustrated working on this assignment. The professor has provided very little information on how to complete this, and when I have asked for more details on how it should be done, he will only say it is involving string comparisons. I've tried to research the topic but I can't seem to find anything that pertains to this type of feature in the way that I am supposed to implement it. Does not help to be trying to learn how opening/reading/writing files works in C at the same time as string comparison, etc.

Is there a resource that would be helpful for this? I am very, very frustrated. I don't want anyone to do my work for me but without understanding what is needed to accomplish this, I feel really at a loss.

There was no limit on the history specified. It appears that what I am supposed to do is replicate the history features of csh.

I found another piece of code from a student who I believe may be doing something similar:

Code:

while(fgets(input, sizeof(input), stdin) != NULL){
 
    filePrint = fopen(".simpleshell_history", "a");
    fileRead = fopen(".simpleshell_history", "r");      
 
    count++;
    fprintf(filePrint, "%d - %s", count, input);
    fclose(filePrint);
 
    if (strcmp(input,"history")==0){
        printf("%sn", input);
        fseek(fileRead, 0, SEEK_SET);
        int x = 0;
        while ((x = fgetc(fileRead)) != EOF){
            printf("%c", x); 
        }
    }
}

However, I tried running it just to see if it was even a reasonable start for the task, and the history started over at 1 every time the shell program was launched. So, it did not work. I am hoping to implement this in the simplest way possible but nothing I have tried thus far has worked.