Bash script to loop through output from AWS Command Line Client

Question

I'm getting a list of EC2 instances and then trying to loop through them but for some reason I'm not able to get the loop to work.

output="$(aws ec2 describe-instances --filters 'Name=tag:Environment,Values=development' --query '[Reservations[*].Instances[*].PublicDnsName]' --output text)"

echo $output displays something like:

ec2-55-55-555-555.eu-west-1.compute.amazonaws.com
ec2-66-66-666-666.eu-west-1.compute.amazonaws.com

Then I create an array like this:

instances=(${output//'\n'/ })

echo ${instances[0]} and echo ${instances[1]} gives the correct output.

And then try to iterate through the array:

for i in $instances; do echo instance: "$i"; done

But I get:

instance: ec2-55-55-555-555.eu-west-1.compute.amazonaws.com ec2-66-66-666-666.eu-west-1.compute.amazonaws.com

Instead of:

instance: ec2-55-55-555-555.eu-west-1.compute.amazonaws.com
instance: ec2-66-66-666-666.eu-west-1.compute.amazonaws.com

What am I doing wrong? And is there a better way to loop through the results, maybe rather using the json output format?

I've tried that, it echos the whole variable. Doesn't split the lines. — Mikhail Janowski
– Mikhail Janowski, Commented Apr 6, 2016 at 13:41
Just add a line separator with: for i in $instances; do echo instance: "$i"$'\n'; done — Simone
– Simone, Commented Apr 6, 2016 at 14:14
Also see Bash FAQ 001 for how to properly read line-by-line from a stream. — Etan Reisner
– Etan Reisner, Commented Apr 6, 2016 at 14:53

krishna_mee2004 · Accepted Answer · 2018-02-28 12:25:56Z

27

I am not sure if you got an answer for this question. Will this help?

for dns in $(aws ec2 describe-instances --region ap-northeast-1 --query 'Reservations[*].Instances[*].PublicDnsName' --output text) ; do echo $dns ; done

answered Feb 28, 2018 at 12:25

krishna_mee2004

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1 Comment

wheeleruniverse Over a year ago

How can we do this with multiple columns?

Ion G. · Accepted Answer · 2016-11-20 16:35:15Z

1

For windows cli:

aws ec2 describe-instances --query "Reservations[].Instances[].InstanceId" > instances

FOR /f %i IN (instances) DO aws ec2 terminate-instances --instance-ids %i

answered Nov 20, 2016 at 16:35

Ion G.

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2 Comments

Ganesh Sittampalam Over a year ago

The question asks for a bash script

Jehong Ahn Over a year ago

But useful. Vote up.

Dave Shaw · Accepted Answer · 2022-11-02 14:07:50Z

1

This also works for me, add it to a bash array:

for instance in $(aws ec2 describe-instances --filters "Name=tag:Application,Values=yourValue" "Name=tag:Environment,Values=development" --query 'Reservations[*].Instances[*].InstanceId' --output text); do envInstances+=(${instance}); done

for i in ${envInstances[@]}; do echo "hello $i"; done

hello i-instance1
hello i-instance12
hello i-instance16

edited Nov 2, 2022 at 14:07

answered Nov 2, 2022 at 13:18

Dave Shaw

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Sebastian Barthelmess · Accepted Answer · 2023-01-12 20:45:52Z

1

Not sure if you just gave up, but in BASH, better to just do this:

OUTPUT=($(aws ec2 describe-instances --filters 'Name=tag:Environment,Values=development' --query '[Reservations[].Instances[].PublicDnsName]' --output text))

then (if you want a count)

echo "${#OUTPUT[@]} instances found."

Good luck!

answered Jan 12, 2023 at 20:45

Sebastian Barthelmess

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1 Comment

Fabio Moratti Over a year ago

This solved a similar issue for me. The key is to use parentheses around the command substitution "$()": var=($(command))

donhector · Accepted Answer · 2023-04-27 15:47:55Z

0

One liner using xargs:

aws ec2 describe-instances --filters 'Name=tag:Environment,Values=development' --query '[Reservations[*].Instances[*].PublicDnsName]' --output text | xargs --no-run-if-empty -n1 echo 'Instance:'

edited Apr 27, 2023 at 15:47

answered Apr 27, 2023 at 15:22

donhector

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