Print code-fenced sections of a Markdown document

Question

Original code and demo at this gist.

Given a Markdown document like

Here is some text,
and some more text.
```javascript
const message = "This is JavaScript!";
```
More text follows, and then
```javascript
console.log(message);
```

I want to print out the sections in code fences, not including the code fences, separated by a single blank line:

const message = "This is JavaScript!";

console.log(message);

I came up with the following AWK script, which seems to do the job nicely:

#!/usr/bin/awk -f
BEGIN { in_code_block = 0 }
/^```/ {
    if (!in_code_block) {
        in_code_block = 1;
        first_line = 1;
    } else {
        in_code_block = 0;
        print "";
    }
}
{
    if (in_code_block && !first_line) {
        print;
    }
    first_line = 0;
}

A goal is for the script to be dependency-minimal. I don't want to have to install an implementation of CommonMark or an Erlang environment. AWK fits this bill well.

Correspondingly, a non-goal is for this script to be correct in all cases: I’m happy to accept false positives on lines starting with ```inline code``` like this, and similar edge cases.

I’m mostly looking for critique of my AWK, with respect to which I am a total newbie. But any comments are welcome!

Answer 1

You could shorten the code with the next statement , which skips the current line.

See in GNU.org AWK manual Next-Statement.

Also you can use your variable as a condition to the command without additional if() inside.

BEGIN { in_code_block = 0 }
/^```/ {
        if (in_code_block)
            print "";
        in_code_block = ! in_code_block;
        next
}
in_code_block { print; }

Tested with GNU Awk 4.1.3.

Answer 2

While your code looks ok, it could be improved greatly by making use of RS (record separator) and NR number of record, provided you're using GNU awk.

 awk -v RS='```[a-z]*\n' '(NR+1)%2' file

In this case RS is set such that it is catching everything between triple backticks with optional text.

The only awk statement is to print one record out of two.

Answer 3

The Code looks perfect to me.

I thought about using the flip-flop operator, but since you take additional action at the beginning and the end of the code block, this may be difficult in this case.

/^```/, /^```/ { ... }

Maybe you want to experiment with that idea nevertheless. It may prove valuable in the future.