Deregisters AWS ECS task definitions using an optional filter expression

aws_dereg_task_def.sh

#!/bin/bash

# Deregisters AWS ECS task definitions based on a filter expression. The optional --dry-run 
# argument can be used to test filter expressions before deleting.

TASK_DEF_FILTER=""
DRY_RUN="N"
THIS_SCRIPT=$0

function usage() {
    echo ""
    echo "Usage: $THIS_SCRIPT [--dry-run] [filter_expression]"
    echo "Where:"
    echo "  --dry-run: print what log groups would be deleted without deleting"
    echo "  filter_expression: expression used to filter task definitions to deregister"
    echo ""
}

function deregister_task_definition() {
    if [ "$DRY_RUN" == "Y" ]; then
        echo "Dry-Run: would deregister task definition: $1"
    else
        echo "Deleting task definition: $1"
        aws ecs deregister-task-definition --task-definition $1 > /dev/null
    fi
}

function deregister_task_definitions() {
    aws ecs list-task-definitions --query 'taskDefinitionArns[*]' --output table | \
        awk '{print $2}' | \
        grep "$TASK_DEF_FILTER" | \
        while read -a tmp_arr; do for x in "${tmp_arr[@]}"; do deregister_task_definition $x; done; done
}

# Make sure region is either set for profile or as environment variable.
CONFIG_REGION=`aws configure get region`

if [[ -z "$AWS_DEFAULT_REGION" ]] && [[ -z "$CONFIG_REGION" ]] ; then
    echo "Region is required. Please configure a default AWS region for this profile using 'aws configure' or set AWS_DEFAULT_REGION environment variable."
    exit 1
fi

# Process command-line arguments.
for var in "$@"
do
    if [ "$var" == "--dry-run" ]; then
        DRY_RUN="Y"
    else
        TASK_DEF_FILTER="$var"
    fi
done

if [ -z "$TASK_DEF_FILTER" ]; then
    # No filter expression provided which means all log groups will be deleted for the 
    # default region. Prompt user to make sure they know what they are about to do.
    read -p "Are you sure you want to deregister ALL task definitions in default region (y/n)?" choice
    case "$choice" in 
        y|Y ) deregister_task_definitions;;
        n|N ) echo "Exiting without deregistering task definitions" && usage && exit 1;;
        * ) echo "Invalid; exiting" && usage && exit 2;;
    esac
else
    deregister_task_definitions
fi