CODEWITHSUNDEEP
bashamazon-web-servicesamazon-ec2aws-cli
Alex
Alex

Reputation: 2805

Show error message on null return for AWS CLI describe-instances

I've got a bash script calling for the IPs of various instances based on a parameter from the user. Right now if their query doesn't match the script doesn't return anything at all, not even null. I'd love to incorporate some kind of error handling to prompt the user to retry. This could be anything from an inbuilt AWS function to a custom error message, I'm not picky.

My script is as follows;

#!/usr/bin/env bash
set -e

#READ ARGUMENTS PASSED IN - expects stack name
if [ "$#" != 1 ]; then
    echo "Illegal number of parameters.  Expecting 1: stack name"
    exit 1
fi

name=$1

aws ec2 describe-instances --query "Reservations[].Instances[].[PublicIpAddress,Tags[?Key=='Name'].Value]" --filter Name=tag:Name,Values=${name} --output text

If it succeeds I'll get something like 

00.00.00.000
name-of-instance

but if it fails I get nothing.

Is there a way to prompt the user or otherwise show an error message if an aws describe-instances returns no matches?

Upvotes: 0

Views: 3522

Answers (2)

helloV
helloV

Reputation: 52433

output=`aws ec2 describe-instances --query "Reservations[].Instances[].[PublicIpAddress,Tags[?Key=='Name'].Value]" --filter Name=tag:Name,Values=${name} --output text`

if [ -n "$output" ]; then
    echo "$output"
else
    echo "No such instance $name exists"
fi

Upvotes: 3

Mark B
Mark B

Reputation: 200988

Capture the output into a variable first like so: 

output=$(aws ec2 describe-instances --query "Reservations[].Instances[].[PublicIpAddress,Tags[?Key=='Name'].Value]" --filter Name=tag:Name,Values=${name} --output text)

Then check the content of output. If there is something there just echo it to the screen. If there isn't, show your custom error message.

Upvotes: 3

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