Create JSON file using jq - json

Question

I'm trying to create a JSON file by executing the following command:
jq --arg greeting world '{"hello":"$greeting"}' > file.json
This command stuck without any input. While
jq -n --arg greeting world '{"hello":"$greeting"}' > file.json
doesn't parse correctly. I'm just wondering is really possible to create a JSON file.

Answer 1

So your code doesn't work because included the variable inside double quotes which gets treated as string. That is why it is not working
As #Jeff Mercado, pointed out the solution is
jq -n --arg greeting world '{"hello":$greeting}' > file.json
About the - in a name. This is actually possible. But as of now this is not available in released version of jq. If you compile the master branch of jq on your system. There is a new variable called $ARGS.named which can be used to access the information.
I just compiled and check the below command and it works like a charm
./jq -n --arg name-is tarun '{"name": $ARGS.named["name-is"]}'
{
"name": "tarun"
}

Answer 2

$ARGS provides access to named (--arg name value) and positional (--args one two three) arguments from the jq command line, and allows you to build up objects easily & safely.
Named arguments:
$ jq -n '{christmas: $ARGS.named}' \
--arg one 'partridge in a "pear" tree' \
--arg two 'turtle doves'
{
"christmas": {
"one": "partridge in a \"pear\" tree",
"two": "turtle doves"
}
}
Positional arguments:
$ jq -n '{numbers: $ARGS.positional}' --args 1 2 3
{
"numbers": [
"1",
"2",
"3"
]
}
Note you can access individual items of the positional array, and that the named arguments are directly available as variables:
jq -n '{first: {name: $one, count: $ARGS.positional[0]}, all: $ARGS}' \
--arg one 'partridge in a "pear" tree' \
--arg two 'turtle doves' \
--args 1 2 3
{
"first": {
"name": "partridge in a \"pear\" tree",
"count": "1"
},
"all": {
"positional": [
"1",
"2",
"3"
],
"named": {
"one": "partridge in a \"pear\" tree",
"two": "turtle doves"
}
}
}

Answer 3

To add to what Jeff and Tarun have already said, you might want to use the \() string interpolation syntax in your command. eg.
jq -n --arg greeting world '{"hello":"\($greeting)"}'
for me this produces
{
"hello": "world"
}
Regarding your reply to Jeff's comment, the argument name you choose has to be a valid jq variable name so an arg like greeting-for-you won't work but you could use underscores so greeting_for_you would be ok. Or you could use the version Tarun described.