Update 4_2__Interlude_Using_JQ.md

4_2__Interlude_Using_JQ.md

@@ -1 +1,40 @@
-[TBD]
+# Interlude: Using JQ
+
+> **NOTE:** This is a draft in progress, so that I can get some feedback from early reviewers. It is not yet ready for learning.
+
+Creating a raw transaction revealed how more complex bitcoin-cli results can't be easily saved into command-line variables. The answer is JQ, which allows you to filter out individual elements from more complex JSON data.
+
+## Install JQ
+
+JQ is available from a [Github repository](https://stedolan.github.io/jq/). Just download for Linux, OS X, or Windows, as appropriate.
+
+Once you've downloaded the binary, you can install it on your system:
+```
+$ mv jq-linux64 jq
+$ sudo /usr/bin/install -m 0755 -o root -g root -t /usr/local/bin jq
+```
+## Use JQ to Capture a JSON Object Key-Values
+
+In the previous section, the use of `signrawtransaction` offered the first example of not being able to easily capture data into variables due to the use of JSON:
+```
+$ bitcoin-cli signrawtransaction $rawtxhex
+{
+  "hex": "0200000001735dfa1584b930a78ad2c1d6db72dd2a80ae5e5d552ad97e19f1d50d41fdd6d8000000006a47304402202210ce4b2a037da02622c380278cd79fec4e0e016e66f3eb894a2dcbb9ee998f02202cac167e6abdbbf08af139fb7c6b86e9d2e58e5516cd566ae2d54953ead9923b012102111bb978a3c93a00038ae344a1a017d7fee8a9be9d0558b5793ce6f440704a96ffffffff01b0e78604000000001976a914e7c1345fc8f87c68170b3aa798a956c2fe6a9eff88ac00000000",
+  "complete": true
+}
+```
+The simplest way to use JQ is to use it as a pipe for output and include a `jq -r .key` argument to capture the raw output key-value. For example:
+```
+$ bitcoin-cli signrawtransaction $rawtxhex | jq -r .hex
+0200000001735dfa1584b930a78ad2c1d6db72dd2a80ae5e5d552ad97e19f1d50d41fdd6d8000000006a47304402202210ce4b2a037da02622c380278cd79fec4e0e016e66f3eb894a2dcbb9ee998f02202cac167e6abdbbf08af139fb7c6b86e9d2e58e5516cd566ae2d54953ead9923b012102111bb978a3c93a00038ae344a1a017d7fee8a9be9d0558b5793ce6f440704a96ffffffff01b0e78604000000001976a914e7c1345fc8f87c68170b3aa798a956c2fe6a9eff88ac00000000
+```
+With that tool in hand, you can capture information from JSON objects to command-line variables, as usual:
+```
+$ signedtx=$(bitcoin-cli signrawtransaction $rawtxhex | jq -r .hex)
+$ echo $signedtx
+0200000001735dfa1584b930a78ad2c1d6db72dd2a80ae5e5d552ad97e19f1d50d41fdd6d8000000006a47304402202210ce4b2a037da02622c380278cd79fec4e0e016e66f3eb894a2dcbb9ee998f02202cac167e6abdbbf08af139fb7c6b86e9d2e58e5516cd566ae2d54953ead9923b012102111bb978a3c93a00038ae344a1a017d7fee8a9be9d0558b5793ce6f440704a96ffffffff01b0e78604000000001976a914e7c1345fc8f87c68170b3aa798a956c2fe6a9eff88ac00000000
+$ bitcoin-cli sendrawtransaction $signedtx
+3f9ccb6e16663e66dc119de1866610cc4f7a83079bfec2abf0598ed3adf10a78
+```
+## Use JQ to Capture a JSON Array Key-Values
+