[pta_workflow] Adds intro to automation

intro_to_plaintextaccounting/workshop/0250_basic_automation.md

@@ -1,4 +1,58 @@
-# Quick and Easy Report Automation
+# Quick and Easy Report Automation {#sec:automation}
+
+It's pretty clear from the previous few chapters that constantly typing out
+each `ledger` command would become laborious quickly.
+If you're working through this document, you are probably comfortable
+or will soon find yourself comfortable with some light programming, so you
+might be tempted to _script_ these executions in something like
+@lst:simple_script.
+
+Listing: A simple `ledger` script {#lst:simple_script}
+
+```{.bash pipe="tee simple_script.sh" .numberLines}
+#!/usr/bin/env bash
+TX_RECORD="${1}"                  # pass the transaction record in as the first arg
+LEDGER_BIN="$(command -v ledger)" # find the ledger command
+
+# Guard against a missing ledger binary
+if [[ -z "${LEDGER_BIN}" ]]; then
+  echo "ledger isn't found in your PATH, please install it."
+  exit 1
+fi
+
+# Assemble a convenient way to constantly invoke the program
+FILE_ARG="-f ${TX_RECORD}"
+LEDGER="${LEDGER_BIN} ${FILE_ARG}"
+
+echo "Net worth:"
+${LEDGER} balance ^Assets ^Liabilities
+
+YEAR="${2:-$(date +%Y)}"
+echo "Cashflow for ${YEAR}:"
+${LEDGER} --begin "${YEAR}" --end "$(( ++YEAR ))" balance ^Income ^Expenses
+```
+
+As @lst:simple_script_exec shows, this is a pretty cool first attempt.
+
+Listing: The simple script from @lst:simple_script passed `ex.ledger` {#lst:simple_script_exec}
+
+```{pipe="sh"}
+bash simple_script.sh ex.ledger 2017
+```
+
+@Lst:simple_script has a simple way to ensure that the `ledger` command
+exists on lines 2-9.
+It takes the transaction record as the first parameter on line 1.
+It builds a convenience variable on lines 12-13 to make executing `ledger` easier.
+It executes ledger to produce a net worth report (@sec:networth) on line 16.
+It takes an optional second parameter on line 18 for the year to use in the
+cash flow report (@sec:cashflow) it executes on line 20.
+
+This is a good start and a rational way to automate reporting.
+However, you can quickly take this to the next logical step by shifting your
+thinking from producing output in the console or a text file to treating
+`ledger` as a type of compiler or conversion tool that produces objects:
+reports.
 
 ## Thinking in Reports