How to use variable with jq cmd in shell-CodePudding

I am facing issue with below commands. I need to use variable but it is returning me null whereas when I hardcode its value, it return me correct response. Can anybody help me whats the correct way of writing this command? My intension is to pull value of corresponding key passed as a variable?

temp1="{    \"SSM_DEV_SECRET_KEY\": \"Smkfnkhnb48dh\",     \"SSM_DEV_GRAPH_DB\": \"Prod=bolt://neo4j:[email protected]:7687\",  \"SSM_DEV_RDS_DB\": \"sqlite:////var/local/ecosystem_dashboard/config.db\",     \"SSM_DEV_SUPPERUSER_USERNAME\": \"admin\",    \"SSM_DEV_SUPPERUSER_PASSWORD\": \"9dW6JE8@KH9qiO006\"   }"

var_name=SSM_DEV_SECRET_KEY
echo $temp1 | jq -r '.SSM_DEV_SECRET_KEY'  <----- return Smkfnkhnb48dh // output
echo $temp1 | jq -r '."$var_name"'  <---- return null
echo $temp1 | jq -r --arg var_name "$var_name" '."$var_name"'  <---- return null , alternative way

Update: I am adding actual piece of where I am trying to use above fix. My intension is to first read all values which start with SSM_DEV_... and then get there original values from aws than replace it in. one key pair look like this --> SECRET_KEY=$SSM_DEV_SECRET_KEY

temp0="dev"
temp1="DEV"
result1=$(aws secretsmanager get-secret-value --secret-id "xxx-secret-$temp0" | jq '.SecretString')
while IFS= read -r line; do
    if [[ "$line" == *"=\$SSM_$temp1"* ]]; then
        before=${line%%"="*}
        after=${line#*"="}
        var_name="${after:1}"
        jq -r --arg var_name "$var_name" '.[$var_name]' <<< "$result1"
    fi
done < sample_file.txt

Fix: I have solved my issue which was of carriage return character. Below cmd help me:

var_name=`echo ${after:1} | tr -d '\r'`
jq -r --arg var_name "$var_name" '.[$var_name]' <<< "$result1"

CodePudding user response：

You'll need to use Generic Object Index (.[$var_name]) to let jq know the variable should be seen as a key

The command should look like:

jq -r --arg var_name "$var_name" '.[$var_name]' <<< "$temp1"

Wich will output:

Smkfnkhnb48dh

Note: <<< "$temp1" instead off the echo

CodePudding user response：

Let's look at the following statement:

echo $temp1 | jq -r '."$var_name"'  <---- return null

Your problem is actually with the shell quoting and not jq. The single quotes tell the shell not to interpolate (do variable substitution) among other things (like escaping white space and preventing globing). Thus, jq is receiving literally ."$var_name" as it's script - which is not what you want. You simply need to remove the single quotes and you'll be good:

echo $temp1 | jq -r ."$var_name"  <---- Does this work?

That said, I would never write my script that way. I would definitely want to include the '.' in the quoted string like this:

echo $temp1 | jq -r ".$var_name"  <---- Does this work?

Some would also suggest that you quote "$temp1" as well (typically all variable references should be quoted to protect against white space, but this is not a problem with echo):

echo "$temp1" | jq -r ".$var_name"  <---- Does this work?