shell script returning null output

Question

I am not able to debug why it is returning

null

value. Can some-one please help into this.

Code -

getJSONParamater() {
       echo "Before : $1 $2 $3"
       eval "$3=$(cat $1 | jq '."$2"')"
       echo "After : $1 $2 $3"
}

return_value='default'
getJSONParamater etl-without-transformation.json  success_email return_value

echo $return_value

@Inian - I just tried it and it works for me with double quotes — Smeeheey
– Smeeheey, Commented Jun 10, 2016 at 9:04
@devsda presumably its because cat ... | jq ... command is returning null — Smeeheey
– Smeeheey, Commented Jun 10, 2016 at 9:07
To debug a shell script, put set -x at the top. Then it will display each line as it executes it, so you can see what's going wrong. — Barmar
– Barmar, Commented Jun 10, 2016 at 9:11
At the very least, use declare instead of eval (although there are even better alternatives) to protect against (some) unintended code evaluation. An extreme example is getJSONParameter f.json value ":; echo hi; name", which would echo "hi" before setting name equal to the result of the command. — chepner
– chepner, Commented Jun 10, 2016 at 13:06

Andreas Louv · Accepted Answer · 2016-06-10 09:21:13Z

4

jq '."$2"' will send literal ."$2" as a expression for jq, what you want is:

jq --arg key "$2" '.[$key]' "$1"

Also removed useless use of cat.

I don't quite understand what you want with the eval part? But I guess you are trying to set return_value to the result from jq?

getJSONParameter() {
  jq --arg key "$2" '.[$key]' "$1"
}

return_value="$(getJSONParameter "etl-without-transformation.json" "success_email")"

edited Jun 10, 2016 at 9:21

answered Jun 10, 2016 at 9:15

Andreas Louv

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Comments

peak · Accepted Answer · 2016-06-10 14:26:03Z

1

Another way to do it by using global variable:

return_value='default'
getJSONParamater() {
       return_value=$(cat "$1" | jq "$2")
}
getJSONParamater etl-without-transformation.json  .success_email
echo $return_value

edited Jun 10, 2016 at 14:26

peak

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answered Jun 10, 2016 at 9:56

Sourabh Gupta

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