Split a JSON file into separate files - json

Question

I have a large JSON file that is an object of objects, which I would like to split into separate files name after object keys. Is it possible to achieve this using jq or any other off-the-shelf tools?
The original JSON is in the following format
{ "item1": {...}, "item2": {...}, ...}
Given this input I would like to produce files item1.json, item2.json etc.

Answer 1

This should give you a start:
for f in `cat input.json | jq -r 'keys[]'` ; do
cat input.json | jq ".$f" > $f.json
done
or when you insist on more bashy syntax like some seem to prefer:
for f in $(jq -r 'keys[]') ; do
jq ".[\"$f\"]" < input.json > "$f.json"
done < input.json

Answer 2

Here's a solution that requires only one call to jq:
jq -cr 'keys[] as $k | "\($k)\n\(.[$k])"' input.json |
while read -r key ; do
read -r item
printf "%s\n" "$item" > "/tmp/$key.json"
done
It might be faster to pipe the output of the jq command to awk, e.g.:
jq -cr 'keys[] as $k | "\($k)\t\(.[$k])"' input.json |
awk -F\\t '{ print $2 > "/tmp/" $1 ".json" }'
Of course, these approaches will need to be modified if the key names contain characters that cannot be used in filenames.

Answer 3

Is it possible to achieve this using jq or any other off-the-shelf tools?
It is. xidel can also do this very efficiently.
Let's assume 'input.json' :
{
"item1": {
"a": 1
},
"item2": {
"b": 2
},
"item3": {
"c": 3
}
}
Inefficient Bash method:
for f in $(xidel -s input.json -e '$json()'); do
xidel -s input.json -e '$json("'$f'")' > $f.json
done
For every object key another instance of xidel is called to parse the object. Especially when you have a very large JSON this is pretty slow.
Efficient file:write() method:
xidel -s input.json -e '
$json() ! file:write(
.||".json",
$json(.),
{"method":"json"}
)
'
One xidel call creates 'item{1,2,3}.json'. Their content is a compact/minified object, like {"a": 1} for 'item1.json'.
xidel -s input.json -e '
for $x in $json() return
file:write(
concat($x,".json"),
$json($x),
{
"method":"json",
"indent":true()
}
)
'
One xidel call creates 'item{1,2,3}.json'. Their content is a prettified object (because of {"indent":true()}), like...
{
"a": 1
}
...for 'item1.json'. Different query (for-loop), same result.
This method is multitudes faster!