Small Shell Implementation

Note: This is a rather quick explanation of my SMALLSH assignment, I'll update this later to be a beginer friendly tutorial including a why and how I reached the conclusions I did, what resources I used to get there and an explanation of the sytsem calls used. In the current state it's really just a highlight of some blog features like syntax highlighting.

A link to my github repo for your reference, this includes a testscript you can run, as well as a modularized version. HERE

wordsplit()

• Splits input line into word tokens
• Handles escapes, whitespace, comments
• Populates words array

size_t wordsplit(char const *line) {
  size_t wlen = 0;
  size_t wind = 0;
  char const *c = line;
  
  for (;*c && isspace(*c); ++c); /* discard leading space */

  for (; *c;) { // iterate until NULL character 
    if (wind == MAX_WORDS) break;
    /* read a word */
    if (*c == '#') break;
    for (;*c && !isspace(*c); ++c) {
      if (*c == '\\') ++c;
      
      void *tmp = realloc(words[wind], sizeof **words * (wlen + 2));
      
      if (!tmp) err(1, "realloc 1");
      
      words[wind] = tmp;
      words[wind][wlen++] = *c; 
      words[wind][wlen] = '\0';
    }
    ++wind;
    wlen = 0;
    
    for (;*c && isspace(*c); ++c);
  }
  
  return wind;
  }

param_scan()

• Finds parameter tokens like $!, $$, ${var}
• Sets start and end pointers for each

expand()

• Expands parameters like $!, $$ with values
• Uses param_scan() and build_str()
• Returns expanded string

build_str()

• Helper to build up expanded strings
• Appends strings/ranges to base string

tokenize()

• Parses I/O redirects, background ops
• Builds argument array for execvp()

check_builtin()

• Checks for builtin commands like cd, exit
• Provides custom handling

execute()

• Forks and executes commands
• Manages I/O redirection
• Waits/handles child processes

manage_background()

• Checks and handles completed background processes

reset_flags()

• Resets I/O redirect flags for next loop