update

#! /usr/bin/env bash

# Update root README.md with links to HOWTO entries.

owd="$(pwd)"
trap "{ cd '$owd'; exit 1; }" ERR
set -o errtrace     # Trap in functions and subshells.
set -o pipefail     # Fail if any pipeline command fails.
shopt -s lastpipe   # Execute last pipeline command in the current shell.
shopt -s nullglob   # Expand no-match globs to nothing rather than themselves.

function info () { echo "$*" 1>&2; }
function error () { info "$*"; exit 1; }

# Extract the #-heading from the first line of an .md file.
#
function heading () # <md-file>
{
  local r
  r=$(sed -rn -e '1s/^#+ *(.+[^ ]) *$/\1/p;q' "$1")

  if [[ -z "$r" ]]; then
    error "no #-header on first line of $1"
  fi

  echo "$r"
}

o=README.md

# Preserve the heading before overwriting the file.
#
h=$(heading "$o")

printf "# %s\n\n" "$h" >$o

for f in $(find entries -type f -name '*.md' | sort); do
  h=$(heading "$f")
  printf "[%s](%s)\n\n" "$h" "$f" >>$o
done