Shell script for replacing placeholders in files in a portable-ish manner

replace_placeholders.sh

#!/usr/bin/env bash
#
# Helper functions for replacing placeholders in files.
#
# Distributed under terms of the MIT license.

set -euo pipefail
IFS=$'\n\t'

# Print example usage of the script.
usage() {
  local script_name script_name="$(printf "%s\n" "$(basename "$0")")"
cat <<EOF
USAGE: $script_name ACTION [OPTIONS]
EXAMPLES:
  $script_name --my-placeholder-name "my-placeholder-value"
EOF
  exit 0
}

# Utility function for asking for confirmation
confirm() {
  local query yn
  query="$1"
  while true; do
    read -rp "$query " yn
    case $yn in
      yes ) return 0;;
      [nN]* ) return 1;;
      * ) printf "Please answer yes or no.\n";;
    esac
  done
}

# Replace placeholders in a predefined set of files
# The characters `<` and `>` are used as delimiters to define a placeholder.
#
# Append `|strip` to the name of the placeholder (e.g., `<my-placeholder|strip>`)
# to remove everything except "standard" characters (alphanumeric, hyphen, underscore or period) in the desired replacement value.
#
# Append `|lowercase` to the name of the placeholder (e.g., `<my-placeholder|lowercase>`)
# to force the desired replacement value to lowercase.
replace_placeholders() {
  local placeholders values search_files timestamp \
    i placeholder value f
  placeholders=()
  values=()
  while [ -n "${1:-}" ]; do
    case "$1" in
      --*) placeholders+=("${1#"--"}"); shift; if test -n "${1:-}"; then values+=("$1"); shift; else echo "Missing placeholder value"; exit 1; fi;;
      *) echo "Unknown parameter format '$1'"; exit 1 ;;
    esac
  done
  search_files=()
  while read -r -d ''; do
    search_files+=("$REPLY")
  done < <(find . \( \
    -name "node_modules" -prune -false \
    -o -wholename "./Jenkinsfile" \
    -o -wholename "*/src/config.ts" \
    \) -print0)
  timestamp="$(date +%s)"
  if [ "${#search_files[@]}" -gt 0 ]; then
    printf "Found the following files:\n---\n"
    printf "%s\n" "${search_files[@]}"
    printf "\n\n"
    if [ ! "${AUTO_CONFIRM:-false}" = "true" ]; then
      if ! confirm "Do you want to replace placeholders in these files?"; then
        exit 1
      fi
    fi
  fi
  for i in "${!placeholders[@]}"; do
    placeholder="${placeholders[i]}"
    value="${values[i]}"
    for f in "${search_files[@]}"; do
      # GNU and FreeBSD sed work in different ways. This command should work for both
      sed -i."${timestamp}.tmp" \
        -e "s/<$placeholder>/$value/g" \
        -e "s/<${placeholder}[|]strip>/$(echo "$value" | sed 's/[^a-zA-Z0-9_.-]//g')/g" \
        -e "s/<${placeholder}[|]lowercase>/$(echo "$value" | tr '[:upper:]' '[:lower:]')/g" \
        "$f" && test -f "$f.$timestamp.tmp" && rm "$f.$timestamp.tmp"
    done
  done
}

main() {
  if [ $# -eq 0 ]; then
    usage
  fi
  case "$1" in
    --help)
      usage
      ;;
    *)
      replace_placeholders "$@"
      ;;
  esac
}

main "$@"