Variable Variables in Shell

Tags: March 10, 2020 8:12 PM
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Subtitute Variable inside Variable in Bash

Example below is using Bash for variable variables subtitution.

$ hello="Hello World"
$ foobar="hello"
$ echo "${!foobar}"
Hello World

Subtitute Variable inside Variable using eval

This is for other shell which do not recognize "${!}" syntax. It utilise eval so use it with caution.

$ hello="Hello World"
$ foobar="hello"
$ eval echo "\$${foobar}"
Hello World

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Terraform: Force Destroy Resource when prevent_destroy is true

Tags: March 3, 2020 6:55 AM
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How to Force Destroy Resource in Terraform

Terraform resource that having lifecycle prevent_destroy = true can not be destroyed. You need to manually edit the file inplace and change the value prevent_destroy to false manually each time you want to destroy the resource. Instead of having to edit manually and make git status dirty we can automate this using simple shell script.

Automate Force Destroy Resource in Terraform

The idea is simple.

  1. Search all *.tf files and look the value of prevent_default = true to prevent_default = false
  2. Run terraform destroy command
  3. Revert the changes back to prevent_default = true
Here is the implementation in Bash.
#!/bin/bash

$ find . -name '*.tf' -type f \
-exec perl -i -pe 's@prevent_destroy = true@prevent_destroy = false@g' {} \;

# Run terraform destroy
[ "$IS_PLAN" = "yes" ] && terraform plan -destroy || terraform destroy $@

# Revert the changes
$ find . -name '*.tf' -type f \
 -exec perl -i -pe 's@prevent_destroy = false@prevent_destroy = true@g' {} \;
Save the file with name e.g: terraform-force-destroy.sh. To issue terraform plan -destroy command use the following.
$ IS_PLAN=yes bash terraform-force-destroy.sh
To force destroy the resource use the following command.
$ bash terraform-force-destroy.sh -auto-approve
You can give normal terraform's arguments just like the original terraform destroy.

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