How to write a bash function that adds a bash variable to a json file with jq?

Question

I would like to add bash variables to a some JSON file with jq. The following method works:

jq --arg VAR "$VAR" '.+{VAR:$VAR}' my.json > my.tmp.json && mv my.tmp.json my.json

with VAR being a bash variable. But as I'm adding many variables I would like to extract a function like the following:

#$1 Variable Name; The entry {"$1": "$($1)"} should be added to my.json
config_add() {
    COMMAND="jq --arg VAR \"\$VAR\" '.+{VAR:\$VAR}' my.json"
    #Replace VAR with the argument
    ${COMMAND//VAR/$1} my.json > my.json.tmp && my.json.tmp my.json
}

But for any variant I try I receive:

jq: error: syntax error, unexpected INVALID_CHARACTER, expecting $end (Unix shell quoting issues?) at <top-level>, line 1:'.+{MYVAR:$MYVAR}'

Any Ideas what is happening here? How would one quote it correctly? Thank you!

peak · Accepted Answer · 2020-06-05 23:52:43Z

2

If the strategy you have in mind depends on a bash function having access to global variables, then it would be better to adopt an alternative approach, such as illustrated here:

config_add() {
    local VAR="$1"
    local VALUE="$2"
    jq --arg VAR "$VAR" --arg VALUE "$VALUE" '.+{($VAR): $VALUE}' > my.json.tmp && my.json.tmp my.json 
}

Invocation examples

x=myvar
myvar=foo

config_add x "$x"

config_add "$x" "${!x}"

For the record

export x=xyzzy
jq -n --arg a x '{($a): $ENV[$a]}'
{
  "x": "xyzzy"
}

edited Jun 5, 2020 at 23:52

answered Jun 5, 2020 at 13:26

peak

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