Detects changes in a file.

file_watch.sh

#!/usr/bin/env bash
# file_watch.sh
# ------------------------------------------------------------------------------
# Description:
#   Watches a file for changes.
#   Includes output on inode changes as that may be desirable in some scenarios.
#   NOTE: ... Just use inotifywait.
#
# Usage:
#   ./file_watch <path/to/file>
#
# Example:
#   Reload a config file automatically while editing it:
#   NOTE: See this article if you want to use inodewait.
#     - https://cyral.com/blog/how-to-auto-reload-nginx/
#       while read line; do
#         if [[ $line =~ "change" ]]; then
#           nginx -t && /etc/init.d/nginx reload
#         fi
#       done< <(./file_watch.sh /etc/nginx/conf.d/default.conf)
# ------------------------------------------------------------------------------

file=$1

function logger2() {
  [[ $1 -eq 0 ]] && echo -e "$(date --utc +'%FT%T.%3NZ') - \e[01;30;41mEMERGENCY\e[0m: ${*:2}"
  [[ $1 -eq 1 ]] && echo -e "$(date --utc +'%FT%T.%3NZ') - \e[01;31;43mALERT\e[0m: ${*:2}"
  [[ $1 -eq 2 ]] && echo -e "$(date --utc +'%FT%T.%3NZ') - \e[01;97;41mCRITICAL\e[0m: ${*:2}"
  [[ $1 -eq 3 ]] && echo -e "$(date --utc +'%FT%T.%3NZ') - \e[01;31mERROR\e[0m: ${*:2}"
  [[ $1 -eq 4 ]] && echo -e "$(date --utc +'%FT%T.%3NZ') - \e[01;33mWARNING\e[0m: ${*:2}"
  [[ $1 -eq 5 ]] && echo -e "$(date --utc +'%FT%T.%3NZ') - \e[01;30;107mNOTICE\e[0m: ${*:2}"
  [[ $1 -eq 6 ]] && echo -e "$(date --utc +'%FT%T.%3NZ') - \e[01;39mINFO\e[0m: ${*:2}"
  [[ $1 -eq 7 ]] && echo -e "$(date --utc +'%FT%T.%3NZ') - \e[01;97;46mDEBUG\e[0m: ${*:2}"
  [[ $1 -eq 9 ]] && echo -e "$(date --utc +'%FT%T.%3NZ') - \e[01;32mSUCCESS\e[0m: ${*:2}"
}

if [[ $# -ne 1 ]]; then
  logger2 3 "Exactly 1 argument is required. It MUST be an existing file."
  exit 1
fi

if [[ ! -f $file ]]; then
  logger2 3 "The path provided is not a file."
fi

get_file_inode() {
  stat -c '%i' "$file"
}

detect_inode_change() {
  if [[ "$file_inode" != $(get_file_inode) ]]; then
    logger2 4 "inode change detected in file: $file"
    #exit 1
    file_inode=$(get_file_inode)
  fi
}

get_file_md5sum() {
  md5sum "$file" | awk '{print $1}'
}

detect_md5sum_change() {
  if [[ "$file_md5sum" != $(get_file_md5sum) ]]; then
    logger2 4 "md5sum change detected in file: $file"
    # exit 1
    file_md5sum=$(get_file_md5sum)
  fi
}

file_inode=$(get_file_inode)
file_md5sum=$(get_file_md5sum)

while true; do
  detect_inode_change
  detect_md5sum_change
  sleep 1
done