check_page_update - Check if content of a web page has been updated

#!/bin/bash
# Checks if content of a web page has been changed.
# NB! Set Nagios service parameter "max_check_attempts" to 1 for proper operation.
# Requires: wget, sha256sum
# Provided by itefix.net

# Exit codes
OK=0
WARNING=1
CRITICAL=2
UNKNOWN=3

exitcode=$UNKNOWN
codetext=("Ok" "Warning" "Critical" "Unknown")

# Usage help
usage() {

  text="
USAGE: ${0} -u <url> -p <working folder> [-c | -w]
-u <url> : url of the content (required)
-p <path>: writable folder for temporary storage (required)
-c : return critical if changed
-w : return warning if changed
"
  echo "$text"

  exit $exitcode
}

# check for command line arguments
while getopts "u:p:wch" option
do
  case "$option" in
    u) url=$OPTARG;;
    p) path=$OPTARG;;
    c) exitcode=$CRITICAL;;
    w) exitcode=$WARNING;;
    h) usage;;
    *) usage;;
  esac
done

if [ -z "$url" ] || [ -z "$path" ]
then
  usage
fi

# use url hash value asa path base
pathbase=$(echo $url | sha256sum | cut -d ' ' -f 1)
curr_hash_path="$path/$pathbase.current"
prev_hash_path="$path/$pathbase.previous"

# Create a previous copy if not exist
if [ ! -f "$prev_hash_path" ]; then
    touch $prev_hash_path
fi

# Use a hash value instead of the whole content
wget -qO- $url | sha256sum > $curr_hash_path
modified=$(diff $curr_hash_path $prev_hash_path)

if [ ! -z "$modified" ]; then
    echo "$url content has changed."
    cp $curr_hash_path $prev_hash_path
    exit $exitcode
fi

echo "No changes in $url content."
exit $OK