Passing JSON arguments (not simple strings) to jq

Question

How do I pass in bash variables into a jq --arg parameter?

All I can get to work is this:

FINAL_JSON= #some JSON

PAYLOAD=$(echo $FINAL_JSON | jq ' {
"attachments": .
} ')

What's bothering me is that echo $FINAL_JSON thing. I should be able to pass in variables in jq??

PAYLOAD=$(jq -n --arg attach "$FINAL_JSON" '{ 
"attachments":$attach
}')

But all that does is pass the JSON in as a string. Without quotes " around the $FINAL_JSON I get this error:

error: syntax error, unexpected $end
{1 compile error

in general, always quote your echo --> echo "$FINAL_JSON" — fedorqui
– fedorqui, Commented Jun 2, 2015 at 14:59
What's the meaning of FINAL_JSON=$(jq -n '[]') ? It simply returns a literal [] . What means # add stuff to FINAL_JSON ? — hek2mgl
– hek2mgl, Commented Jun 2, 2015 at 15:04
I'm still not able to get your question. Can you add one self-contained example which shows how do you not want to do it and one self-contained example which you want it to look like? (The latter can be pseudo code or course, since you don't have it already) — hek2mgl
– hek2mgl, Commented Jun 2, 2015 at 15:12

Charles Duffy · Accepted Answer · 2015-06-02 15:25:55Z

3

A simple transformation of your working code (also moving to lower-case variable names, as per convention for variable names not reserved for shell or system use):

payload=$(jq -n --argfile attach <(printf '%s\n' "$final_json") '{ 
"attachments":$attach
}')

I'm sticking with --argfile here since it parses the file's contents as JSON; using --arg wouldn't have that effect.

The <(...) syntax is process substitution, which is replaced with a filename for a named pipe or temporary file connected to the content in question.

However, you can also use --arg, and apply the fromjson filter to parse as JSON:

payload=$(jq -n --arg attach "$final_json" '{ 
"attachments":$attach|fromjson
}')

edited Jun 2, 2015 at 15:25

answered Jun 2, 2015 at 15:16

Charles Duffy

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1 Comment

Jeff Mercado Over a year ago

--argjson is also an option, if you're using 1.5.

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