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--- docs:guide-developer:jshn [2021/02/15 03:29] – old revision restored (2021/02/13 23:27) stokito
+++ docs:guide-developer:jshn [2024/08/03 12:52] (current) – [See also] stokito
@@ Line 13: / Line 13: @@
 # generating json data
 json_init
+json_add_int "code" "0"
 json_add_string "msg" "Hello, world!"
 json_add_object "test"
 json_add_int "testdata" "1"
 json_close_object
-MSG=`json_dump`
+MSG_JSON=`json_dump`
-# MSG now contains: { "msg": "Hello, world!", "test": { "testdata": 1 } }
+# the MSG_JSON var now contains: { "code": 0, "msg": "Hello, world!", "test": { "testdata": 1 } }
-# parsing json data
+# parsing json data from the MSG_JSON variable
-json_load "$MSG"
+local var1 code msg # declare local variables to load data into
-json_select test
+json_load "$MSG_JSON"
-json_get_var var1 testdata
+json_select test # go into the object inside of the "test" field
-json_select ..
+json_get_var var1 testdata # first is var name "var1" then the JSON field name "testdata"
-json_get_var var2 msg
+json_select .. # go back to the upper level
-echo "msg: $var2 - testdata: $var1"
+# load the "code" field into corresponding code var, and the "msg" field into the msg var
+json_get_vars code msg
+echo "code: $code, msg: $msg, testdata: $var1"
 </code>
@@ Line 71: / Line 75: @@
 ==== More complicated examples ====
+=== Parse file example ===
 Given the file:
 <code - /data1.json>
@@ Line 101: / Line 105: @@
 </code>
-Parse arrays examзle. Given the file:
+=== Parse arrays example ===
+Given the file:
 <code - /data2.json>
 {
@@ Line 122: / Line 128: @@
 then
   json_select lan
-  idx=1
+  idx=1 # note that array element position starts from 1 not, 0
   while json_is_a ${idx} string  ## iterate over data inside "lan" object
   do
@@ Line 132: / Line 138: @@
 </code>
+=== Parse list of objects ===
+The example will download electricity hourly prices for Finland in JSON and parse it.
+The prices JSON looks like
+<code - prices.json>
+{
+  "prices": [
+    {
+      "date": "2024-08-03T11:00:00.000Z",
+      "value": 6.41
+    },
+    {
+      "date": "2024-08-03T12:00:00.000Z",
+      "value": 4.1
+    },
+  ]
+}
+</code>
+Script to parse it:
+<code bash>
+#!/bin/sh
+set -e
+. /usr/share/libubox/jshn.sh
+date=$(date -u +%Y-%m-%dT%H:00:00.000Z)
+# download prices JSON via wget in quiet mode with output to stdout that will be saved to a variable PRICES_JSON
+PRICES_JSON=$(wget -qO - "https://sahkotin.fi/prices?start=$date")
+exit_status=$?
+# check exit code: if any error then exit
+if [ $exit_status -ne 0 ]; then
+   >&2 echo "error $exit_status"
+   exit $exit_status
+fi
+json_load "$PRICES_JSON"
+json_select "prices"
+idx=1 # note that array element position starts from 1 not, 0
+# iterate over data inside "price" array until elements are objects
+while json_is_a $idx object
+do
+  json_select  $idx
+  # now parse {"date": "2024-08-04T21:00:00.000Z", "value": 22.58}
+  json_get_var price_date "date"
+  echo "price_date: $price_date"
+  json_get_var price_value "value"
+  echo "price_value: $price_value"
+  idx=$(( idx + 1 ))
+  json_select .. # go back to the upper level to the prices array
+done
+echo "Total parsed $idx"
+</code>
 ===== json_for_each_item =====
@@ Line 144: / Line 204: @@
 . /usr/share/libubox/jshn.sh
-json_init
 json_load_file /data2.json
@@ Line 152: / Line 211: @@
 json_for_each_item "dump_item" "ip_addrs"
+</code>
+===== json_get_values =====
+To get all values of an array use the ''json_get_values'':
+<code bash>
+#!/bin/sh
+. /usr/share/libubox/jshn.sh
+json_load '{"alist":[1,2]}'
+json_get_values values "alist"
+echo "${values}" #=> 1 2
+# print comma separated
+echo "${values// /, }" #=> 1, 2
+</code>
+===== Get all fields into variables =====
+Get all fields and declare variables for them:
+<code bash>
+json_load '{"params":{"id": 1, "name": "Alice"}}'
+json_select "params"
+json_get_keys keys
+for key in $keys
+do
+  json_get_var "$key" "$key"
+done
+echo "$id" #=> 1
+echo "$name" #=> Alice
 </code>
@@ Line 366: / Line 454: @@
 ==== jq ====
-[[https://stedolan.github.io/jq/|jq]] jq is a lightweight and flexible command-line JSON processor.
+[[https://stedolan.github.io/jq/|jq]] jq is a flexible command-line JSON processor that is very popular for scripting.
-You can install it with ''opkg install jq''
+It's not installed by default in OpenWRT because is too big (more than 200Kb) so to install use ''opkg update; opkg install jq''
 By default it just colorize an output e.g. ''cat /etc/board.json | jq''
+==== See also ====
+  * [[https://github.com/burningtree/awesome-json|Awesome JSON]] A curated list of awesome JSON libraries and resources.
+  * [[https://github.com/yurt-page/openwrt-script-samples|OpenWrt script samples]]
+  * [[https://forum.openwrt.org/t/writing-shell-scripts-support-topic/206144|Writing shell scripts support forum topic]]