• Uncategorized

About json : Passing-bash-variable-to-jq

Question Detail

I have written a script to retrieve certain value from file.json. It works if I provide the value to jq select, but the variable doesn’t seem to work (or I don’t know how to use it).

#!/bin/sh

#this works ***
projectID=$(cat file.json | jq -r ‘.resource[] | select(.username==”[email protected]”) | .id’)
echo “$projectID”

[email protected]

#this does not work *** no value is printed
projectID=$(cat file.json | jq -r ‘.resource[] | select(.username==”$EMAILID”) | .id’)
echo “$projectID”

Question Answer

Consider also passing in the shell variable (EMAILID) as a jq variable (here also EMAILID, for the sake of illustration):
projectID=$(jq -r –arg EMAILID “$EMAILID” ‘
.resource[]
| select(.username==$EMAILID)
| .id’ file.json)

Postscript
For the record, another possibility would be to use jq’s env function for accessing environment variables. For example, consider this sequence of bash commands:
[email protected] # not exported
EMAILID=”$EMAILID” jq -n ‘env.EMAILID’

The output is a JSON string:
[email protected]

……………………………………………………
I resolved this issue by escaping the inner double quotes

projectID=$(cat file.json | jq -r “.resource[] | select(.username==\”$EMAILID\”) | .id”)

……………………………………………………
Little unrelated but I will still put it here,
For other practical purposes shell variables can be used as –

value=10
jq ‘.”key” = “‘”$value”‘”‘ file.json

……………………………………………………
Posting it here as it might help others. In string it might be necessary to pass the quotes to jq. To do the following with jq:

.items[] | select(.name==”string”)

in bash you could do

EMAILID=$1
projectID=$(cat file.json | jq -r ‘.resource[] | select(.username==’\”$EMAILID\”‘) | .id’)

essentially escaping the quotes and passing it on to jq
……………………………………………………
It’s a quote issue, you need :

projectID=$(
cat file.json | jq -r “.resource[] | select(.username==’$EMAILID’) | .id”
)

If you put single quotes to delimit the main string, the shell takes $EMAILID literally.

“Double quote” every literal that contains spaces/metacharacters and every expansion: “$var”, “$(command “$var”)”, “${array[@]}”, “a & b”. Use ‘single quotes’ for code or literal $’s: ‘Costs $5 US’, ssh host ‘echo “$HOSTNAME”‘. See
http://mywiki.wooledge.org/Quotes
http://mywiki.wooledge.org/Arguments
http://wiki.bash-hackers.org/syntax/words
……………………………………………………
Jq now have better way to access environment variables, you can use env.EMAILID:
projectID=$(cat file.json | jq -r “.resource[] | select(.username==env.EMAILID) | .id”)

……………………………………………………
Another way to accomplish this is with the jq “–arg” flag.
Using the original example:

#!/bin/sh

#this works ***
projectID=$(cat file.json | jq -r ‘.resource[] |
select(.username==”[email protected]”) | .id’)
echo “$projectID”

[email protected]

# Use –arg to pass the variable to jq. This should work:
projectID=$(cat file.json | jq –arg EMAILID $EMAILID -r ‘.resource[]
| select(.username==”$EMAILID”) | .id’)
echo “$projectID”

See here, which is where I found this solution:
https://github.com/stedolan/jq/issues/626
……………………………………………………
I know is a bit later to reply, sorry. But that works for me.

export K8S_public_load_balancer_url=”$(kubectl get services -n ${TENANT}-production -o wide | grep “ingress-nginx-internal$” | awk ‘{print $4}’)”

And now I am able to fetch and pass the content of the variable to jq

export TF_VAR_public_load_balancer_url=”$(aws elbv2 describe-load-balancers –region eu-west-1 | jq -r ‘.LoadBalancers[] | select (.DNSName == “‘$K8S_public_load_balancer_url'”) | .LoadBalancerArn’)”

In my case I needed to use double quote and quote to access the variable value.

Cheers.
……………………………………………………
I also faced same issue of variable substitution with jq. I found that –arg is the option which must be used with square bracket [] otherwise it won’t work.. I am giving you sample example below:
RUNNER_TOKEN=$(aws secretsmanager get-secret-value –secret-id $SECRET_ID | jq ‘.SecretString|fromjson’ | jq –arg kt $SECRET_KEY -r ‘.[$kt]’ | tr -d ‘”‘)

……………………………………………………
In case where we want to append some string to the variable value and we are using the escaped double quotes, for example appending .crt to a variable CERT_TYPE; the following should work:
$ CERT_TYPE=client.reader
$ cat certs.json | jq -r “.\”${CERT_TYPE}\”.crt” #### This will *not* work #####
$ cat certs.json | jq -r “.\”${CERT_TYPE}.crt\””

You may also like...

Leave a Reply

Your email address will not be published. Required fields are marked *

This site uses Akismet to reduce spam. Learn how your comment data is processed.