jq - parse structure and save values in bash variable - json

Question

I have a json input as follow
{
"unique": 1924,
"coordinates": [
{
"time": "2015-01-25T00:00:01.683",
"xyz": [
{
"z": 4,
"y": 2,
"x": 1,
"id": 99,
"inner_arr" : [
{
"a": 1,
"b": 2
},
{
"a": 3,
"b": 4
}
]
},
{
"z": 9,
"y": 9,
"x": 8,
"id": 100,
"inner_arr" : [
{
"a": 1,
"b": 2
},
{
"a": 3,
"b": 4
}
]
},
{
"z": 9,
"y": 6,
"x": 10,
"id": 101,
"inner_arr" : [
{
"a": 1,
"b": 2
},
{
"a": 3,
"b": 4
}
]
}
]
},
{
"time": "2015-01-25T00:00:02.790",
"xyz": [
{
"z": 0,
"y": 3,
"x": 7,
"id": 99,
"inner_arr" : [
{
"a": 1,
"b": 2
},
{
"a": 3,
"b": 4
}
]
},
{
"z": 4,
"y": 6,
"x": 2,
"id": 100,
"inner_arr" : [
{
"a": 1,
"b": 2
},
{
"a": 3,
"b": 4
}
]
},
{
"z": 2,
"y": 9,
"x": 51,
"id": 101,
"inner_arr" : [
{
"a": 1,
"b": 2
},
{
"a": 3,
"b": 4
}
]
}
]
}
]
}
I want to parse this input with jq and store values in bash arrays:
#!/bin/bash
z=()
x=()
y=()
id=()
a=()
b=()
jq --raw-output '.coordinates[] | .xyz[] | (.z) as $z, (.y) as $y,7 (.x) as $x, (.id) as $id, .inner_arr[].a $a, .inner_arr[].b as $b | $z, $y, $x, $id, $a, $b' <<< "$input"
echo -e "${z}"
Expected output for above echo command:
4
9
9
0
4
2
echo -e "${a}"
Expected output for above echo command:
1
3
1
3
1
3
1
3
1
3
1
3
How can I do it with jq with a single jq call looping through all arrays in a cascading fashion?
I want to save CPU by calling jq just once and extract all single or array values.

Answer 1

You cannot set environment variable directly from jq (cf. manual). What you can do is to generate a series of bash declarations for the declare builtin. I suggest to store the declarations in an intermediate bash array (with mapfile) processed directly by declare so that you can stay away from hazardous commands like eval.
mapfile -t < <(
jq --raw-output '
def m(exp): first(.[0] | path(exp)[-1]) + "=(" + (map(exp) | #sh) + ")";
[ .coordinates[].xyz[] ]
| m(.x), m(.y), m(.z), m(.id), m(.inner_arr[].a), m(.inner_arr[].b)
' input
)
declare -a "${MAPFILE[#]}"
The jq script packs all xyz objects in a single array and filters it with the m function for each field represented as a path expression. The function returns a string formatted as field=(val1 val2... valN), where the field name is the last component of the path expression, i.e. x for .x and a for .inner_arr[].a (extracted on the first item of the array).
Then you can check the shell variables with declare -p var or ${var[#]}. ${var} refers to the first element only.
declare -p MAPFILE
declare -p z
echo a: "${a[#]}" / size = ${#a[#]}
declare -a MAPFILE=([0]="x=(1 8 10 7 2 51)" [1]="y=(2 9 6 3 6 9)" [2]="z=(4 9 9 0 4 2)" [3]="id=(99 100 101 99 100 101)" [4]="a=(1 3 1 3 1 3 1 3 1 3 1 3)" [5]="b=(2 4 2 4 2 4 2 4 2 4 2 4)")
declare -a z=([0]="4" [1]="9" [2]="9" [3]="0" [4]="4" [5]="2")
a: 1 3 1 3 1 3 1 3 1 3 1 3 / size = 12