bash script to create a Table of Contents from a Markdown file

md-toc.sh

#!/bin/bash
# md-toc.sh
############
# Generates a Table of Contents getting a markdown file as input.
#
# Inspiration for this script:
# https://medium.com/@acrodriguez/one-liner-to-generate-a-markdown-toc-f5292112fd14
#
# The list of invalid chars is probably incomplete, but is good enough for my
# current needs.
# Got the list from:
# https://github.com/thlorenz/anchor-markdown-header/blob/56f77a232ab1915106ad1746b99333bf83ee32a2/anchor-markdown-header.js#L25


# needed for elementInArray()
shopt -s extglob


joinBy() {
  local IFS="$1"
  echo "${*:2}"
}


elementInArray() {
  local element="$1"
  local array=("${@:2}")
  [[ "$element" == @($(joinBy '|' "${array[@]//|/\\|}")) ]]
}


toc() {
  local invalidChars="'[]/?!:\`.,()*\";{}+=<>~$|#@&–—"
  local inputFile="$1"

  [[ -f "${inputFile}" ]] || return 1

  local line
  local level
  local title
  local anchor
  local anchorList=()
  local i

  while IFS='' read -r line || [[ -n "${line}" ]]; do
    level="$(echo "${line}" | sed -E 's/^#(#+).*/\1/; s/#/    /g; s/^    //')"
    title="$(echo "${line}" | sed -E 's/^#+ //')"
    anchor="$(echo "${title}" | tr '[:upper:] ' '[:lower:]-' | tr -d "$invalidChars")"

    if elementInArray "${anchor}" "${anchorList[@]}"; then
      # limitation: allows only 100 repeated anchors
      for i in {1..100}; do
        elementInArray "${anchor}-${i}" "${anchorList[@]}" && continue
        anchor="${anchor}-${i}"
        break
      done
    fi

    echo "${level}- [${title}](#${anchor})"
    anchorList+=("${anchor}")
  done <<< "$(grep -E '^#{2,10} ' "${inputFile}" | tr -d '\r')"
}

main() {
    toc "$@"
}

[[ "$0" == "$BASH_SOURCE" ]] && main "$@"

Thanks so much!

I used this script to build a new one based on the previously utility I was using: doctoc. Hence, you specify a file, and it modifies current table of contents block or creates a new one on top of the file.

I will track my own changes here: https://gitlab.com/pedrolab/doctoc.sh

#!/bin/bash

# motivation to rewrite a simple alternative to doctoc: How Much Do You Trust That Package? Understanding The Software Supply Chain https://www.youtube.com/watch?v=fnELtqE6mMM
# src https://gist.github.com/meleu/57867f4a01ede1bd730f14b2f018ae89

############
# Generates a Table of Contents getting a markdown file as input.
#
# Inspiration for this script:
# https://medium.com/@acrodriguez/one-liner-to-generate-a-markdown-toc-f5292112fd14
#
# The list of invalid chars is probably incomplete, but is good enough for my
# current needs.
# Got the list from:
# https://github.com/thlorenz/anchor-markdown-header/blob/56f77a232ab1915106ad1746b99333bf83ee32a2/anchor-markdown-header.js#L25
#

INVALID_CHARS="'[]/?!:\`.,()*\";{}+=<>~$|#@&–—"

check() {

    # src https://stackoverflow.com/questions/6482377/check-existence-of-input-argument-in-a-bash-shell-script
    if [ -z "$1" ]; then
        echo "Error. No argument found. Put as argument a file.md"
        exit 1
    fi

    [[ ! -f "$1" ]] && echo "Error. File not found" && exit

}

toc() {

    local line
    local level
    local title
    local anchor
    local output

    while IFS='' read -r line || [[ -n "$line" ]]; do
        level="$(echo "$line" | sed -E 's/^#(#+).*/\1/; s/#/    /g; s/^    //')"
        title="$(echo "$line" | sed -E 's/^#+ //')"
        anchor="$(echo "$title" | tr '[:upper:] ' '[:lower:]-' | tr -d "$INVALID_CHARS")"
        output=$output"$level- [$title](#$anchor)\n"
    done <<< "$(grep -E '^#{2,10} ' "$1" | tr -d '\r')"

    echo "$output"

}

insert() {

    local toc_text="$2"
    local appname='doctoc.sh'
    # inspired in doctoc lines
    local start_toc="<!-- START $appname generated TOC please keep comment here to allow auto update -->"
    local info_toc="<!-- DO NOT EDIT THIS SECTION, INSTEAD RE-RUN $appname TO UPDATE -->"
    local end_toc="<!-- END $appname generated TOC please keep comment here to allow auto update -->"

    toc_block="$start_toc\n$info_toc\n**Table of Contents**\n\n$toc_text\n$end_toc"

    # search multiline toc block -> https://stackoverflow.com/questions/2686147/how-to-find-patterns-across-multiple-lines-using-grep/2686705
    if grep -Pzl "(?s)$start_toc.*\n.*$end_toc" $1 &>/dev/null; then
        echo -e "\n  Updated content of $appname block for $1 succesfully\n"
        # src https://askubuntu.com/questions/533221/how-do-i-replace-multiple-lines-with-single-word-in-fileinplace-replace
        sed -i ":a;N;\$!ba;s/$start_toc.*$end_toc/$toc_block/g" $1
    else
        echo -e "\n  Created $appname block for $1 succesfully\n"
        sed -i 1i"$toc_block" "$1"
    fi

}

main() {

    check "$1"
    toc_text=$(toc "$1")
    insert "$1" "$toc_text"

}

[[ "$0" == "$BASH_SOURCE" ]] && main "$@"