retroforth/literate/Unu.md

Unu

unu
(verb) (-hia) pull out, withdraw, draw out, extract.

Unu is a tool for extracting fenced code blocks from Markdown documents.

I always found documenting my projects annoying. Eventually I decided to start mixing the code and commentary using Markdown. Unu is the tool I use to extract the sources from the original files. I've found that this makes it easier for me to keep the commentary up to date, and has lead to better commented code.

The Code

First, headers:

#include <stdio.h>
#include <stdlib.h>
#include <string.h>
#include <ctype.h>

I use this for readability purposes.

#define KiB * 1024

The read_line function is intended to read in a single line into a target buffer. This considers a line to end with either a \n or EOF.

void read_line(FILE *file, char *line_buffer) {
  int ch, count;

  if (file == NULL || line_buffer == NULL)
  {
    printf("Error: file or line buffer pointer is null.");
    exit(1);
  }

  ch = getc(file);
  count = 0;

  while ((ch != '\n') && (ch != EOF)) {
    line_buffer[count] = ch;
    count++;
    ch = getc(file);
  }

  line_buffer[count] = '\0';
}

The line buffer needs to be big enough for the longest lines in your source files. Here it's set to 16KiB, which suffices for everything I've used Unu with so far.

char source[16 KiB];

Unu looks for Markdown style fenced blocks of code. It supports both backticks and tildes for this. This will return 1 if the line appears to be a start/stop of a fence, or 0 otherwise.

int fenced(char *s)
{
  int a = strcmp(s, "```");
  int b = strcmp(s, "~~~");
  if (a == 0) return 1;
  if (b == 0) return 1;
              return 0;
}

The actual extract function is straightforward.

• open the file
• read each line
  • if in a fenced region, write the lines to stdout
• close the file

void extract(char *fname) {
  char *buffer = (char *)source;
  char fence[4];
  FILE *fp;
  int inBlock;
  inBlock = 0;
  fp = fopen(fname, "r");
  if (fp == NULL)
    return;
  while (!feof(fp)) {
    read_line(fp, buffer);
    strncpy(fence, buffer, 3);
    fence[3] = '\0';
    if (fenced(fence)) {
      if (inBlock == 0)
        inBlock = 1;
      else
        inBlock = 0;
    } else {
      if ((inBlock == 1) && (strlen(buffer) != 0))
        printf("%s\n", buffer);
    }
  }
  fclose(fp);
}

And finally, the main routine, which just runs extract on each specified file.

int main(int argc, char **argv) {
  int i = 1;
  if (argc > 1) {
    while (i < argc) {
      extract(argv[i++]);
    }
  }
  else
    printf("unu\n(c) 2013-2019 charles childers\n\nTry:\n  %s filename\n", argv[0]);
  return 0;
}