Necessary improvements to the shell code

README.md

@@ -1,12 +1,46 @@
-These scripts are designed to be run via a cron job with the MAILTO variable set to generate an email(or any other notification method) when output occurs.
+# Description
 
-Output will occur when an IP is added/removed or changed for the service you are checking.
+The supplied bash scripts are supposed to be run via a cron job and assume that the MAILTO variable in the cron is set to send out a notification email when any IP address change happens.
 
-- `check_events.sh` - Checks events.pagerduty.com for changed IP addressses.
+# Prerequisites to run this script
 
-- `check_mailservers.sh` - Checks acme.pagerduty.com for changed MX record IP addressses.
-(Used when you utilize an email integrated service and need to whitelist outgoing traffic to PagerDuty)
+The scripts depend on the external `dig` command to get the list of IP addresses from the PagerDuty servers. You should be able to install the `dig` command using the following steps:
 
-- `check_webhooks.sh` - Checks webhooks.pagerduty.com for changed IP addressses.
+## On RedHat-based GNU/Linux servers
 
-- `check_webhooks_and_alert.sh` - Same as `check_webhooks.sh` but triggers a PagerDuty incident.
+Install it from the `bind-utils` package available in the repositories.
+
+Command: `dnf install bind-utils`
+
+You will require root permissions to install the package.
+
+## On Debian-based GNU/Linux servers
+
+Install it from the `dnsutils` package available in the repositories.
+
+Command: `apt install dnsutils`
+
+You will require root permissions to install the package.
+
+# Output
+
+It is assumed that there are two scenario's to each script run, which are:
+
+## When the IP addresses change
+
+The script(s) will display a list of all the new IP addresses fetched from the server on the stdout and will send out a notification email to the email address set in the MAILTO variable in the cron.
+
+This notification email may then be captured to initiate an incident in PagerDuty.
+
+## When the IP addresses do not change
+
+There is no change in the files or output on the stdout and no notification email is sent out.
+
+# Description of the files in the repository
+
+| File name | Remarks |
+|-|-|
+| `check_events.sh`      | Checks events.pagerduty.com for changed IP addressses. |
+| `check_mailservers.sh` | Checks `acme.pagerduty.com` for changed MX record IP addressses. (Used when you utilize an email integrated service and need to whitelist outgoing traffic to PagerDuty) |
+| `check_webhooks.sh` | Checks `webhooks.pagerduty.com` for changed IP addressses. |
+| `check_webhooks_and_alert.sh` | Checks `webhooks.pagerduty.com` for changed IP addressses, same as `check_webhooks.sh`, but also triggers a PagerDuty incident. |

check_events.sh

@@ -1,18 +1,29 @@
-#!/bin/bash
+#!/usr/bin/env bash
 
-## This script is designed to be run via a cron job with the MAILTO variable set to generate an email when output occurs (an IP is added/removed/changed)
+# More information on PagerDuty Events - https://support.pagerduty.com/docs/event-management
+# PagerDuty Status Page - https://status.pagerduty.com
 
-if [ -f "events_result.txt" ]; then
-  mv events_result.txt events_result.txt.old
-fi
+## This script is designed to be run via a cron job with the MAILTO variable
+## set to generate an email when output occurs (an IP is added/removed/changed)
 
-dig +short events.pagerduty.com | sort > events_result.txt
+# get the list of IP addresses from the PagerDuty Events URL. Storing in a memory variable to reduce disk access
+events_results_current = $(dig +short events.pagerduty.com | sort)
 
-if [ -f "events_result.txt.old" ]; then
-  DIFF=$(diff -q 'events_result.txt.old' 'events_result.txt' > /dev/null)
+if [ -f "events_results.txt" ]; then
+  # we check for the diff and supress any outputs on the stdout
+  DIFF=$(echo "${events_results_current}" | diff -q 'events_results.txt' - > /dev/null)
+
+  # diff command returns a status code 0 if no change has been detected
   if [ $? -ne 0 ]; then
-    echo "Changes detected! New IPs are:"
-    cat events_result.txt
+    # The script has detected that the list of IP addresses has changed.
+    # we overwrite the existing file with the changed IP addresses.
+    echo ${events_results_current} > events_results.txt
+    # display the output on stdout. MAILTO cron variable takes over the job of sending out an email.
+    echo -e "\nThe script has detected a change in PagerDuty's Events IP addresses. The new IP addresses are:\n\n${events_results_current}"
   fi
-  rm events_result.txt.old
-fi
+else
+  # we fall in this condition when we run the script for the first time
+  # or if the events_results.txt has been deleted
+  # we create a new one and spit the output on the stdout too
+  echo ${events_results_current} | tee events_results.txt 
+fi

check_mailservers.sh

@@ -1,18 +1,28 @@
-#!/bin/bash
+#!/usr/bin/env bash
 
-## This script is designed to be run via a cron job with the MAILTO variable set to generate an email when output occurs (an IP is added/removed/changed)
+# PagerDuty Status Page - https://status.pagerduty.com
 
-if [ -f "mailservers_result.txt" ]; then
-  mv mailservers_result.txt mailservers_result.txt.old
-fi
+## This script is designed to be run via a cron job with the MAILTO variable
+## set to generate an email when output occurs (an IP is added/removed/changed)
 
-dig +short mx acme.pagerduty.com | sed 's/.$//g' | sed 's/^[0-9][0-9]* //g' | xargs dig +short | sort > mailservers_result.txt
+# get the list of IP addresses from the PagerDuty acme URL. Storing in a memory variable to reduce disk access
+mailservers_results_current = $(dig +short mx acme.pagerduty.com | sed 's/.$//g' | sed 's/^[0-9][0-9]* //g' | xargs dig +short | sort)
 
-if [ -f "mailservers_result.txt.old" ]; then
-  DIFF=$(diff -q 'mailservers_result.txt.old' 'mailservers_result.txt' > /dev/null)
+if [ -f "mailservers_results.txt" ]; then
+  # we check for the diff and supress any outputs on the stdout
+  DIFF=$(echo "${mailservers_results_current}" | diff -q 'mailservers_results.txt' - > /dev/null)
+
+  # diff command returns a status code 0 if no change has been detected
   if [ $? -ne 0 ]; then
-    echo "Changes detected! New IPs are:"
-    cat mailservers_result.txt
+    # The script has detected that the list of IP addresses has changed.
+    # we overwrite the existing file with the changed IP addresses.
+    echo ${mailservers_results_current} > mailservers_results.txt
+    # display the output on stdout. MAILTO cron variable takes over the job of sending out an email.
+    echo -e "\nThe script has detected a change in PagerDuty Mailserver's IP addresses. The new IP addresses are:\n\n${mailservers_results_current}"
   fi
-  rm mailservers_result.txt.old
-fi
+else
+  # we fall in this condition when we run the script for the first time
+  # or if the mailservers_results.txt has been deleted
+  # we create a new one and spit the output on the stdout too
+  echo ${mailservers_results_current} | tee mailservers_results.txt
+fi

check_webhooks.sh

@@ -1,18 +1,29 @@
-#!/bin/bash
+#!/usr/bin/env bash
 
-## This script is designed to be run via a cron job with the MAILTO variable set to generate an email when output occurs (an IP is added/removed/changed)
+# PagerDuty Webhooks Documentation - https://support.pagerduty.com/docs/webhooks
+# PagerDuty Status Page - https://status.pagerduty.com
 
-if [ -f "webhooks_result.txt" ]; then
-  mv webhooks_result.txt webhooks_result.txt.old
-fi
+## This script is designed to be run via a cron job with the MAILTO variable
+## set to generate an email when output occurs (an IP is added/removed/changed)
 
-curl -s https://app.pagerduty.com/webhook_ips | tr -d \[\]\" | tr , '\n' | sort > webhooks_result.txt
+# get the list of IP addresses from the PagerDuty Webhooks URL. Storing in a memory variable to reduce disk access
+webhooks_results_current = $(curl -s https://app.pagerduty.com/webhook_ips | tr -d \[\]\" | tr , '\n' | sort)
 
-if [ -f "webhooks_result.txt.old" ]; then
-  DIFF=$(diff -q 'webhooks_result.txt.old' 'webhooks_result.txt' > /dev/null)
+if [ -f "webhooks_results.txt" ]; then
+  # we check for the diff and supress any outputs on the stdout
+  DIFF=$(echo "${webhooks_results_current}" | diff -q 'webhooks_results.txt' - > /dev/null)
+
+  # diff command returns a status code 0 if no change has been detected
   if [ $? -ne 0 ]; then
-    echo "Changes detected! New IPs are:"
-    cat webhooks_result.txt
+    # The script has detected that the list of IP addresses has changed.
+    # we overwrite the existing file with the changed IP addresses.
+    echo ${webhooks_results_current} > webhooks_results.txt
+    # display the output on stdout. MAILTO cron variable takes over the job of sending out an email.
+    echo -e "\nThe script has detected a change in PagerDuty Webhook's IP addresses. The new IP addresses are:\n\n${webhooks_results_current}"
   fi
-  rm webhooks_result.txt.old
-fi
+else
+  # we fall in this condition when we run the script for the first time
+  # or if the webhooks_results.txt has been deleted
+  # we create a new one and spit the output on the stdout too
+  echo ${webhooks_results_current} | tee webhooks_results.txt
+fi

check_webhooks_and_alert.sh

@@ -1,4 +1,4 @@
-#!/bin/bash
+#!/usr/bin/env bash
 # Webhook delivery service IP address change notification script
 #
 # Same as check_webhooks.sh, but triggers a PagerDuty incident if there are changes.