magnetikonline

AWS CLI JMESPath cheatsheet

Random query recipes of JMESPath for the AWS CLI tools that I might have written or stumbled upon.

• Examples
  • List available AWS regions
  • List Lambda functions within AWS account region
  • Test if specific Lambda function exists
  • List Route 53 record names and their type for a zone
  • List CloudWatch log groups

magnetikonline

JavaScript implementation of binary insertion sort

• Random list of ascending numbers generated in resultIndexList as seed list.
• Set of random numbers generated, insert position determined by insertAt() function.
• Each value inserted using resultIndexList.splice() to maintain sort order as progressing.

Reference

• https://en.wikipedia.org/wiki/Insertion_sort
• https://jeffreystedfast.blogspot.com.au/2007/02/binary-insertion-sort.html

magnetikonline

Linux umask table

Umask is determined by subtracting (binary NOT) from the initial masks of:

• File: 666 rw-rw-rw
• Directory: 777 rwxrwxrwx

Therefore:

| Umask | File result | Directory result |

magnetikonline

An example of recursion with Promises

A pattern for recursion with Promises - in this example, walking a directory structure.

Function flow

• readDirRecursive() is called with a starting directory and will itself return a Promise.
• Internally readDir() is called and passed starting directory to read from.
• A list of directory items is returned by getItemList() as a Promise, which in turn is chained to getItemListStat() to stat each item to determine if file or directory.
• Finalised list then passed to processItemList():

magnetikonline

Bash internal field separator (IFS) usage

The IFS internal variable is used to determine what characters Bash defines as word/item boundaries when processing character strings. By default set to whitespace characters of space, tab, and newline.

Running the example ifs.sh, comparing the difference between the default and setting only newline as a boundary we get the following output:

/path/to/first
file
/path/to/second

magnetikonline

Install Git on macOS from source

A quick n' dirty Bash script to install the following:

• autoconf, needed by Git configure.
• git - from source.

Tested successfully under both Intel and M1 (ARM64) based architectures.

Requires as a minimum Xcode CLI tools (no need for a full install). Can be installed via the following:

magnetikonline

NetScaler rewrite action to update a cookie key value

Making a note of this because NetScalers at just awful at anything when it comes to messing with HTTP header cookie values.

So I wish to update the value of a Cookie key of mykey= to mykey=new_value. I can do so with the following rewrite action:

• Type: REPLACE

• Expression to choose target location: HTTP.REQ.HEADER("Cookie")

• Expression:

magnetikonline

List all Git repository objects by size

• Summary
• Example

Summary

Bash script which will:

• Iterate all commits made within a Git repository.

magnetikonline

Stop Python urllib2 following HTTP redirects

By default calling a URL via urllib2 will follow any 30X responses returned, often not what you want.

We can correct this behavior by adding a custom "opener" class to the urllib2 module like so:

import urllib
import urllib2

magnetikonline

Install tig CLI Git repository browser tool

Without the need for Xcode bloat (yay!).

What is tig?: https://github.com/jonas/tig

# install gcc/make/etc.
# note: this will *not* install Xcode - don't be fooled by xcode in CLI command name
$ xcode-select --install