Prepend or replace section numbering for markdown headings

mdheadnum.awk

#!/usr/bin/env -S gawk -f

$1~/^##+$/ && $0!~/Table of Contents$/{
    if (l > length($1)) for (k in num) if (k > length($1)) delete num[k]
    l = length($1)
    num[l] += 1
    r = substr($0, l + 2)

    p = ""; for (i in num) p = p num[i] "."
    if (length(num) > 1) p = substr(p, 0, length(p) - 1)
    gsub("^[0-9.]+ ", "", r)
    print $1, p, r
    next
}

//