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CIDR fit

Python function to determine if a given IPv4 CIDR fits into another.

How cidr_fit(cidr_a,cidr_b) works:

• For both CIDR's given:
  • Splits each CIDR into address and prefix size parts.
  • Converts the address part to a 32 bit binary string.
    • Example: 192.168.0.1 becomes 11000000101010000000000000000001.

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Gmail retention/purge by label Google script

A Google Apps Script which adds pseudo message retention-like policies against specific labels for a Gmail account.

• How it works
• Install
• Reference

How it works

• Apps Script function is called automatically on a regular schedule.
• Script iterates over a set of predefined message labels.

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Add user ssh-agent as daemon to Ubuntu 18.04LTS server

Create a new systemd user unit, which starts ssh-agent upon login to server. Will remain resident until the final session for the user has logged out.

Steps

• Create /etc/systemd/user/ssh-agent.service.

• Run the following commands (under your user account, not root) to install the systemd unit and start:

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Bash shift quirks

When using the shift built-in, have noted this interesting behavior which I have been unable to find documentation for.

Update: the answer was right in front of me, if shift is called with a value greater than arguments available in $1 - $x then it will return with a non zero status - hence the script will halt (since I'm using set -e)!

Using the script test.sh, executed using arguments:

./test.sh apple orange banana
apple

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CloudFormation API Gateway integration to Lambda function

Template that will create the following:

• API Gateway:
  • Deployed as a REGIONAL endpoint.
  • Single root method, accepting POST requests only, with Lambda proxy integration to a target function.
• In-line Python Lambda function echoing back requesting users IP address to API Gateway requests:
  • IAM role for Lambda allowing CloudWatch logs access.
  • Permissions for Lambda that allow API Gateway endpoint to successfully invoke function.

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List AWS AMI IDs for a given marketplace product

Script to return AMI IDs for a given AWS region associated to a marketplace product page. Requires AWS CLI and a valid set of credentials for the aws ec2 describe-images call.

Usage

• Browse the AWS marketplace to locate the product of interest.
• Note the URL of the product page.
• Execute script for the desired region:

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Extract all files at every commit of a Git repository

Bash script to iterate all commits of a given Git repository and extract all files within each commit.

Example

With a Git repository at /path/to/repository and an empty directory at /path/to/output we can run:

./export.sh /path/to/repository /path/to/output

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AWS CloudFormation YAML template - appending to list parameter types

Documenting this here, as I often forget (what I have found) is the best way to do this at the moment.

For example, you have a list of two existing security groups given to a stack and wish to create (and use) a third - attaching all to an ALB:

AWSTemplateFormatVersion: '2010-09-09'
Description: Example template

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Bash getopt long options with values usage example

#!/bin/bash -e

ARGUMENT_LIST=(
  "arg-one"
  "arg-two"
  "arg-three"
)

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MySQL user management cheatsheet

• List all users
• List connected users
• Create user
  • With mysql_native_password identity
  • With auth_socket identity
• Grant user specific permissions to database
• Grant root-like permissions
• List grants for user