Install multiple versions of JDK and switch between them via CLI on MAC OSX:

(Updated to include newer JDK versions)

1) Install the Oracle JDKs from here, as needed for dev work:
1.6: https://www.oracle.com/java/technologies/javase-java-archive-javase6-downloads.html
1.7: https://www.oracle.com/java/technologies/javase/javase7-archive-downloads.html
1.8: https://www.oracle.com/java/technologies/javase/javase8u211-later-archive-downloads.html

1.11: https://www.oracle.com/java/technologies/javase/jdk11-archive-downloads.html

1.17: https://www.oracle.com/java/technologies/downloads/#JDK17

2) Add the following to the ~/.bashrc or ~/.zshrc
#Set JAVA_HOME to latest version of JAVA_HOME (recommended)
export JAVA_HOME=$(/usr/libexec/java_home)
 
#Set alias options to dynamically change JAVA_HOME to particular JDK
alias jdk6=' export JAVA_HOME=$(/usr/libexec/java_home -v 1.6.0) '

alias jdk7=' export JAVA_HOME=$(/usr/libexec/java_home -v 1.7.0) '

alias jdk8=' export JAVA_HOME=$(/usr/libexec/java_home -v 1.8.0) '

alias jdk11=' export JAVA_HOME=$(/usr/libexec/java_home -v 11) '

alias jdk17=' export JAVA_HOME=$(/usr/libexec/java_home -v 17) '

3) To switch between the versions of JDK, run the command jdkXX, for example:

#Default version as listed above will always set the JAVA_HOME to the latest version as determined by java_home:
$ java -version
java version "1.8.0_60"
Java(TM) SE Runtime Environment (build 1.8.0_60-b27)
Java HotSpot(TM) 64-Bit Server VM (build 25.60-b23, mixed mode)
 
$ jdk6
$ java -version
java version "1.6.0_65"
Java(TM) SE Runtime Environment (build 1.6.0_65-b14-468-11M4833)
Java HotSpot(TM) 64-Bit Server VM (build 20.65-b04-468, mixed mode)
 
$ jdk7
$ java -version
java version "1.7.0_72"
Java(TM) SE Runtime Environment (build 1.7.0_72-b14)
Java HotSpot(TM) 64-Bit Server VM (build 24.72-b04, mixed mode)

$ jdk11

$ java -version

java version "11.0.11" 2021-04-20 LTS

Java(TM) SE Runtime Environment 18.9 (build 11.0.11+9-LTS-194)

Java HotSpot(TM) 64-Bit Server VM 18.9 (build 11.0.11+9-LTS-194, mixed mode)

$ jdk17

$ java -version

java version "17" 2021-09-14 LTS

Java(TM) SE Runtime Environment (build 17+35-LTS-2724)

Java HotSpot(TM) 64-Bit Server VM (build 17+35-LTS-2724, mixed mode, sharing)

Show count and instance IDs of existing EC2 instances in all regions of AWS:

I'm kicking myself for not posting this earlier in my past life-- but here's a handy shell script that can list the number of instances in each region in AWS.

Show count and instance IDs of existing EC2 instances in all regions of AWS:

Single line:

Set my AWS profile to my personal account rather than work.  
To setup, use aws --profile personal configure   

$ export aws_profile=personal

If the buffer space can handle long entries, you can run this in a single line, otherwise there's a multi line below to run as a script.

$ for i in $(aws --profile $aws_profile ec2 describe-regions --output json | grep "RegionName" | cut -d '"' -f4 | sort); do export buf=$(aws --profile $aws_profile ec2 --region $i describe-instances --output json | grep InstanceId | cut -d '"' -f4); export buf_num=$(echo $buf | grep -c .); echo "=== $i -> $buf_num instance(s) ===";echo $buf ; done

Multi Line:

Good for placing into a script to run, also listed this way for readability:

#!/bin/bash export aws_profile=personal for i in $(aws --profile $aws_profile ec2 describe-regions --output json| grep "RegionName" | cut -d '"' -f4 | sort); do export buf=$(aws ec2 describe-instances \ --profile $aws_profile \ --region $i \ --output json | \ grep InstanceId | \ cut -d '"' -f4); export buf_num=$(echo $buf | grep -c .); echo "=== $i -> $buf_num instance(s) ==="; echo $buf; done

Sample Output:

=== ap-northeast-1 -> 0 instances === === ap-northeast-2 -> 0 instances === === ap-south-1 -> 0 instances === === ap-southeast-1 -> 0 instances === === ap-southeast-2 -> 0 instances === === ca-central-1 -> 0 instances === === eu-central-1 -> 0 instances === === eu-north-1 -> 0 instances === === eu-west-1 -> 0 instances === === eu-west-2 -> 0 instances === === eu-west-3 -> 0 instances === === sa-east-1 -> 0 instances === === us-east-1 -> 0 instances === === us-east-2 -> 0 instances === === us-west-1 -> 0 instances === === us-west-2 -> 1 instances === i-012345678901234ab