Extract value of json-like variable in bash

Question

I have a variable in bash that is an output of Amazon EMR create command;

CLUSTER=$(aws emr create-cluster ...)
echo $CLUSTER

the output is like this:

{ "ClusterId": "j-9YWMBYN98LN7" }

What I need to do is to extract the value j-9YWMBYN98LN7 to a new variable, something like:

ID=$CLUSTER.(ClusterId)

Of course the above command doesn't work. I have tried with jq but no luck.

ID=$(jq -r '.ClusterId' $CLUSTER)

The thing is I'm not even sure what type $CLUSTER is. How do I extract the value j-9YWMBYN98LN7 there? Thanks

if might not matter, but did you try `ID=$(jq -r '.ClusterId' "$CLUSTER")` ? (dbl-quoting CLUSTER var). Good luck. — shellter, May 05 '16 at 02:34
Doesn't work either, here is the output: `jq: { "ClusterId": "j-1FZMHAPPDD0LG" }: No such file or directory.` Thanks anyway — user3685928, May 05 '16 at 03:24

CS Pei · Answer 1 · 2016-05-05T03:40:58.470

13

If you want to use jq, you can do it this way

 ID=`echo ${CLUSTER} | jq -r '.ClusterId'`

edited May 05 '16 at 03:40

answered May 05 '16 at 02:52

CS Pei

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Thanks but this doesn't work either. I think this $CLUSTER is not json (may be string, I don't know). Here is the output: `cat: {: No such file or directory cat: "ClusterId":: No such file or directory cat: "j-1FZMHAPPDD0LG": No such file or directory cat: }: No such file or directory` – user3685928 May 05 '16 at 03:26
My bad, it should be `echo` instead of `cat`. I corrected my answer and it should work now. – CS Pei May 05 '16 at 03:41
It works now, thanks a lot, but I can only upvote your answer as I have accepted the other one :) – user3685928 May 05 '16 at 05:11
@user3685928 You can (and should) accept this answer instead. – chepner May 10 '16 at 03:51
simple & works ✨ – Rizki Noor Hidayat Wijaya Apr 09 '18 at 01:41

sjsam · Accepted Answer · 2016-05-09T20:58:47.590

5

If

echo $CLUSTER

gives you

{ "ClusterId": "j-9YWMBYN98LN7" }

then

ID=$(awk  'BEGIN{FS="\""}{print $4}' <<< "${CLUSTER}")

should do it.

echo "$ID"
j-9YWMBYN98LN7

edited May 09 '16 at 20:58

answered May 05 '16 at 02:46

sjsam

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This works. Thanks a lot! – user3685928 May 05 '16 at 03:27
@user3685928 : You're welcome pal ! – sjsam May 05 '16 at 05:19
2

This solution works in bash, but not in others shells. This is my variation to ash: `ID=$(echo $CLUSTER | awk 'BEGIN{FS="\""}{print $4}')` – Javier Yáñez Feb 17 '21 at 13:16
@JavierYáñez Cool, Thankfully the question is tagged bash – sjsam Feb 17 '21 at 13:20

score 2 · Answer 3 · answered May 05 '16 at 02:46

2

Try the following:

ID=$(echo "${CLUSTER}" | sed 's/{ "ClusterId": "//' | sed 's/" }//')

That will isolate j-9YWMBYN98LN7, or whatever is between the last set of quotes, into the variable $ID.

I get the feeling there is more to what you need as you are probably planning on using the contents of $ID for something and there may be more efficient ways to capture that value for you. Maybe if you can explain a bit more how you plan on using the value we can provide even more actionable answers.

answered May 05 '16 at 02:46

John Mark Mitchell

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I'm writing a script to automate the process of creating an EMR cluster and adding jobs to it. I need this Cluster ID in the job-adding step like this: `aws emr add-steps --cluster-id $ID`. Again, I'm not sure what type of the variable $CLUSTER here, and I understand that just by giving you guys the output it could be hard – user3685928 May 05 '16 at 03:32
Anyway, the output of your command is still the same as $CLUSTER `{ "ClusterId": "j-1FZMHAPPDD0LG" }` – user3685928 May 05 '16 at 03:33
It is odd that is did not work for you. You can check it via `echo '{ "ClusterId": "j-9YWMBYN98LN7" }' | sed 's/{ "ClusterId": "//' | sed 's/" }//'` For me it did indeed output `j-9YWMBYN98LN7`. No worries though, I like @sjsam 's awk answer better as well. – John Mark Mitchell May 06 '16 at 04:12

Extract value of json-like variable in bash

3 Answers3