jq - Looping through json and concatenate the output to single string-CodePudding

I was currently learning the usage of jq. I have a json file and I am able to loop through and filter out the values I need from the json. However, I am running into issue when I try to combine the output into single string instead of having the output in multiple lines.

File svcs.json:

[ 
 {
   "name": "svc-A",
   "run" : "True"
 },
 {
   "name": "svc-B",
   "run" : "False"
 },
 {
   "name": "svc-C",
   "run" : "True"
 }
]

I was using the jq to filter to output the service names with run value as True

jq -r '.[] | select(.run=="True") | .name ' svcs.json

I was getting the output as follows:

 svc-A
 svc-C

I was looking to get the output as single string separated by commas.

Expected Output:

"svc-A,svc-C"

I tried to using join, but was unable to get it to work so far.

CodePudding user response：

The .[] expression explodes the array into a stream of its elements. You'll need to collect the transformed stream (the names) back into an array. Then you can use the @csv filter for the final output

$ jq -r '[ .[] | select(.run=="True") | .name ] | @csv' svcs.json
"svc-A","svc-C"

But here's where map comes in handy to operate on an array's elements:

$ jq -r 'map(select(.run=="True") | .name) | @csv' svcs.json
"svc-A","svc-C"

CodePudding user response：

Keep the array using map instead of decomposing it with .[], then join with a glue string:

jq -r 'map(select(.run=="True") | .name) | join(",")' svcs.json

svc-A,svc-C

Demo

If your goal is to create a CSV output, there is a special @csv command taking care of quoting, escaping etc.

jq -r 'map(select(.run=="True") | .name) | @csv' svcs.json

"svc-A","svc-C"

Demo