Given a JSON line
{"a":0,"b":{"c":"C"}}{"x":33}{"asd":889}
of 3 independent JSON objects.
And need to handle then one by one. It would be nice to have something like
echo "$json" | jq --first-one
Expected output:
{"a":0,"b":{"c":"C"}}
I found the only command which can remove first object and output others. inputs
echo '{"a":0,"b":{"c":"C"}}{"x":33}{"asd":889}' | jq -c inputs
output:
{"x":33}
{"asd":889}
How to read only first object from input stream and do not touch the rest objects?
Workaround
While writing this Q I found a workaround, but it looks cumbersome
echo '{"a":0,"b":{"c":"C"}}{"x":33}{"asd":889}' | jq -c . | head -1
simply get first line...
Slurping should, in general, be avoided if possible. If your jq has input, you could simply write:
echo '{"a":0,"b":{"c":"C"}}{"x":33}{"asd":889}' |
jq -n input
If your jq does not have input, now would be a great time to upgrade to jq 1.6. If that is not an option, then by all means use the -s option, e.g. jq -s '.[0]'
Related
I am extracting keys from a json with this format:
[
{
"k1":{"k2":4},
"k3":{"k2":6}
}
]
[
{
"k1":{"k2":4},
"k3":{"k2":6}
}
]
I am using this command ["a","b"], (.[] | [.k1.k2,.k3.k2]) | #csv to extract two keys and adding two headers (a, b) to the csv. But The output to this is a header in every other line:
"\"a\",\"b\""
"4,6"
"\"a\",\"b\""
"4,6"
You can see this in this jq play. How can I change to filter to just put header on the first line?
As you have stream in your json, you need inputs instead of .[]
jq -nr '(["a","b"], (inputs | map(.k1.k2,.k3.k2))) | #csv' input-json
Your input is a stream of JSON documents. Thus, your filter gets executed once for each document, including constructing the headers.
One solution would be to use the --slurp or -s option to read in the stream as an array. This, however, would necessitate to go one level deeper in your iteration (.[][] instead of just .[]):
jq -s '["a","b"], (.[][] | [.k1.k2,.k3.k2]) | #csv'
Demo
Another way would be to use inputs which gives you all input documents at once. This, however, would necessitate to iterate over that (input[] instead of .[]) and use the --null-input or -n flag to avoid swallowing up the first elemment:
jq -n '["a","b"], (inputs[] | [.k1.k2,.k3.k2]) | #csv'
Demo
Note: You also may want to use the --raw-output or -r flag to produce raw text instead of JSON when generating the output with #csv (as I already did in the demos).
I have a json file locally called pokemini.json. These are the contents of it;
{"name":"Bulbasaur","type":["Grass","Poison"],"total":318,"hp":45,"attack":49}
{"name":"Ivysaur","type":["Grass","Poison"],"total":405,"hp":60,"attack":62}
{"name":"Venusaur","type":["Grass","Poison"],"total":525,"hp":80,"attack":82}
{"name":"VenusaurMega Venusaur","type":["Grass","Poison"],"total":625,"hp":80,"attack":100}
{"name":"Charmander","type":["Fire"],"total":309,"hp":39,"attack":52}
{"name":"Charmeleon","type":["Fire"],"total":405,"hp":58,"attack":64}
{"name":"Charizard","type":["Fire","Flying"],"total":534,"hp":78,"attack":84}
{"name":"CharizardMega Charizard X","type":["Fire","Dragon"],"total":634,"hp":78,"attack":130}
{"name":"CharizardMega Charizard Y","type":["Fire","Flying"],"total":634,"hp":78,"attack":104}
{"name":"Squirtle","type":["Water"],"total":314,"hp":44,"attack":48}
There are a few types of pokemon in here and I want to do some aggregation with jq.
I could, per example, write this command;
> jq -s -c 'group_by(.type[0]) | .[]' pokemini.json
[{"name":"Charmander","type":["Fire"],"total":309,"hp":39,"attack":52},{"name":"Charmeleon","type":["Fire"],"total":405,"hp":58,"attack":64},{"name":"Charizard","type":["Fire","Flying"],"total":534,"hp":78,"attack":84},{"name":"CharizardMega Charizard X","type":["Fire","Dragon"],"total":634,"hp":78,"attack":130},{"name":"CharizardMega Charizard Y","type":["Fire","Flying"],"total":634,"hp":78,"attack":104}]
[{"name":"Bulbasaur","type":["Grass","Poison"],"total":318,"hp":45,"attack":49},{"name":"Ivysaur","type":["Grass","Poison"],"total":405,"hp":60,"attack":62},{"name":"Venusaur","type":["Grass","Poison"],"total":525,"hp":80,"attack":82},{"name":"VenusaurMega Venusaur","type":["Grass","Poison"],"total":625,"hp":80,"attack":100}]
[{"name":"Squirtle","type":["Water"],"total":314,"hp":44,"attack":48}]
I am aware that the -c flag is what is causing it to print line by line and that I need -s to handle the fact that my json file is more like jsonlines that actualy json. It should also be pointed that out there are only three types of pokemon detected because I can grouping over .type[0] (note that [0]).
I don't get why this does not work though;
> jq -s '.[] | group_by(.type[0])' pokemini.json
jq: error (at pokemini.json:10): Cannot index string with string "type"
group_by/1 expects its input to be an array. By calling .[] first, you are effectively undoing the work of the -s option.
By the way, an alternative to using -s is to use inputs with the -n command-line option, but in this case it makes little difference. When you don’t actually need to read all the entire stream of inputs at once, though, using inputs is in general more efficient.
I have some text that I want to escape to something I can use in JSON.
I can escape the text using jq and display it
normaltext="My normal text that I want to put in \"JSON\""
echo $normaltext | jq --slurp --raw-input
"My normal text that I want to put in \"JSON\"\n"
However, store that command output into a variable, jq doesn't seem to receive the input and just displays the help text.
escapedtext=$(echo $normaltext | jq --slurp --raw-input)
jq - commandline JSON processor [version 1.5-1-a5b5cbe]
Usage: jq [options] [file...]
Your version of jq evidently requires the . filter here, as in:
jq -s -R .
I'm trying to use jq to get a value from the JSON that cURL returns.
This is the JSON cURL passes to jq (and, FTR, I want jq to return "VALUE-I-WANT" without the quotation marks):
[
{
"success":{
"username":"VALUE-I-WANT"
}
}
]
I initially tried this:
jq ' . | .success | .username'
and got
jq: error (at <stdin>:0): Cannot index array with string "success"
I then tried a bunch of variations, with no luck.
With a bunch of searching the web, I found this SE entry, and thought it might have been my saviour (spoiler, it wasn't). But it led me to try these:
jq -r '.[].success.username'
jq -r '.[].success'
They didn't return an error, they returned "null". Which may or may not be an improvement.
Can anybody tell me what I'm doing wrong here? And why it's wrong?
You need to pipe the output of .[] into the next filter.
jq -r '.[] | .success.username' tmp.json
tl;dr
# Extract .success.username from ALL array elements.
# .[] enumerates all array elements
# -r produces raw (unquoted) output
jq -r '.[].success.username' file.json
# Extract .success.username only from the 1st array element.
jq -r '.[0].success.username' file.json
Your input is an array, so in order to access its elements you need .[], the array/object-value iterator (as the name suggests, it can also enumerate the properties of an object):
Just . | sends the input (.) array as a whole through the pipeline, and an array only has numerical indices, so the attempt to index (access) it with .success.username fails.
Thus, simply replacing . | with .[] | in your original attempt, combined with -r to get raw (unquoted output), should solve your problem, as shown in chepner's helpful answer.
However, peak points out that since at least jq 1.3 (current as of this writing is jq 1.5) you don't strictly need a pipeline, as demonstrated in the commands at the top.
So the 2nd command in your question should work with your sample input, unless you're using an older version.
I'm using jq to parse some of my logs, but some of the log lines can't be parsed for various reasons. Is there a way to have jq ignore those lines? I can't seem to find a solution. I tried to use the --seq argument that was recommended by some people, but --seq ignores all the lines in my file.
Assuming that each log entry is exactly one line, you can use the -R or --raw-input option to tell jq to leave the lines unparsed, after which you can prepend fromjson? | to your filter to make jq try to parse each line as JSON and throw away the ones that error.
I have log stream where some messages are in json format.
I want to pipe the json messages through jq, and just echo the rest.
The json messages are on a single line.
Solution: use grep and tee to split the lines in two streams, those starting with "^{" pipe through jq and the rest just echo to terminal.
kubectl logs -f web-svjkn | tee >(grep -v "^{") | grep "^{" | jq .
or
cat logs | tee >(grep -v "^{") | grep "^{" | jq .
Explanation:
tee generates 2nd stream, and grep -v prints non json info, 2nd grep only pipes what looks like json opening bracket to jq.
This is an old thread, but here's another solution fully in jq. This allows you to both process proper json lines and also print out non-json lines.
jq -R . as $line | try (fromjson | <further processing for proper json lines>) catch $line'
There are several Q&As on the FAQ page dealing with the topic of "invalid JSON", but see in particular the Q:
Is there a way to have jq keep going after it hits an error in the input file?
In particular, this shows how to use --seq.
However, from the the sparse details you've given (SO recommends a minimal example be given), it would seem it might be better simply to use inputs. The idea is to process one JSON entity at a time, using "try/catch", e.g.
def handle: inputs | [., "length is \(length)"] ;
def process: try handle catch ("Failed", process) ;
process
Don't forget to use the -n option when invoking jq.
See also Processing not-quite-valid JSON.
If JSON in curly braces {}:
grep -Pzo '\{(?>[^\{\}]|(?R))*\}' | jq 'objects'
If JSON in square brackets []:
grep -Pzo '\[(?>[^\[\]]|(?R))*\]' | jq 'arrays'
This works if there are no []{} in non-JSON lines.