Here are some yearly journal files demonstrating issues and techniques
discussed in the [close docs](https://hledger.org/dev/hledger.html>).

`2021.journal`, `2022.journal` and `2023.journal` each have
only an opening balances transaction and some ordinary transactions. 
These are what you'd get if you started a new file each year
using hledger's `close --open` command or Ledger's `equity` command.
These files show correct balances when used individually, but they can't be combined for a multi-year report;
their opening transactions are redundant and will produce nonsense balances.

To solve this, whenever we transition to a new file we can

- add a counterbalancing [closing transaction](https://hledger.org/hledger.html#close) using `close`.

Also (not necessary for basic personal accounting, but if we want to be fully correct), we should ensure all equity is accounted for:

- where we have used @/@@ notation to convert between commodities, add [equivalent equity postings](https://hledger.org/hledger.html#equity-conversion-postings)
- and consolidate revenues and expenses into equity (AKA [retain earnings](https://hledger.org/hledger.html#close)).

Combining all of these in the right sequence is tricky, so here's an example of fully migrating to a new file at the end of 2021/start of 2022.
`2021-closed.journal` and `2022-closed.journal` are the result of applying this procedure to the 2021 and 2022 journals.
(They are given a different name here for clarity; normally you probably wouldn't change the name.)

First ensure all equity changes are recorded:

```cli
$ hledger -f 2021.journal print --infer-equity          > 2021-closed.journal   # add explicit equity:conversion postings where needed
$ hledger -f 2021-closed.journal close --retain -e 2022 >> 2021-closed.journal  # retain earnings (transfer RX to E)
```

Next migrate asset/liability balances from old file to new file.
(If you want to preserve equity balances too, add a [`type:ALE` argument](https://hledger.org/hledger.html#account-types).)
Note how --open is done first and --close second; or you could --close first and `--open not:desc:closing` second:

```cli
$ hledger -f 2021-closed.journal close --open   -e 2022 >> 2022.journal         # migrate balances (add opening txn to 2022.journal)
$ hledger -f 2021-closed.journal close --close  -e 2022 >> 2021-closed.journal  # migrate balances (add closing txn to 2021.journal)
```

Finally, add a tag like this (manually) to the closing and opening transactions to make them easier to exclude from reports:

```journal
2021-12-31 closing balances  ; start:2022
...
```
```journal
2022-01-01 opening balances  ; start:2022
...
```

Now we can confirm that the accounting equation was preserved in 2021 (Net: is 0).
We must exclude the closing balances transaction to see the end balances:

```cli
$ hledger -f 2021-closed.journal bse not:tag:start=2022
Balance Sheet With Equity 2021-12-31

                                 ||   2021-12-31 
=================================++==============
 Assets                          ||              
---------------------------------++--------------
 assets                          ||           21 
---------------------------------++--------------
                                 ||           21 
=================================++==============
 Liabilities                     ||              
---------------------------------++--------------
---------------------------------++--------------
                                 ||              
=================================++==============
 Equity                          ||              
---------------------------------++--------------
 equity:conversion:A-B:A         ||         -1 A 
 equity:conversion:A-B:B         ||          1 B 
 equity:opening/closing balances ||           20 
 equity:retained earnings        || 1, 1 A, -1 B 
---------------------------------++--------------
                                 ||           21 
=================================++==============
 Net:                            ||            0 
```

We can check the accounting equation for 2022 too, after adding all equity changes:

```cli
$ (hledger -f 2022.journal print --infer-equity; hledger -f 2022.journal close --retain) | hledger -f- bse 
Balance Sheet With Equity 2024-01-19

                          ||   2024-01-19 
==========================++==============
 Assets                   ||              
--------------------------++--------------
 assets                   ||           22 
--------------------------++--------------
                          ||           22 
==========================++==============
 Liabilities              ||              
--------------------------++--------------
--------------------------++--------------
                          ||              
==========================++==============
 Equity                   ||              
--------------------------++--------------
 equity:conversion:A-B:A  ||         -1 A 
 equity:conversion:A-B:B  ||          1 B 
 equity:retained earnings || 1, 1 A, -1 B 
 equity:start             ||           21 
--------------------------++--------------
                          ||           22 
==========================++==============
 Net:                     ||            0 
```

We can see correct balance sheets from any range of files if we exclude all opening/closing transactions except the first:

```cli
$ hledger bs -Y -f 2021-closed.journal -f 2022-closed.journal -f 2023.journal expr:'tag:start=2021 or not tag:start'
$ hledger bs -Y -f 2021-closed.journal -f 2022-closed.journal                 expr:'tag:start=2021 or not tag:start'
$ hledger bs -Y -f 2022-closed.journal -f 2023.journal                        expr:'tag:start=2022 or not tag:start'
$ hledger bs -Y -f 2021-closed.journal                                        expr:'tag:start=2021 or not tag:start'
$ hledger bs -Y -f 2022-closed.journal                                        expr:'tag:start=2022 or not tag:start'
$ hledger bs -Y -f 2023.journal                                               # unclosed file, no query needed
```

And we can see correct income statements from any range of files if we exclude retain earnings transactions:

```cli
$ hledger is -Y -f 2021-closed.journal -f 2022-closed.journal -f 2023.journal not:desc:retain
$ hledger is -Y -f 2021-closed.journal -f 2022-closed.journal                 not:desc:retain
$ hledger is -Y -f 2022-closed.journal -f 2023.journal                        not:desc:retain
$ hledger is -Y -f 2021-closed.journal                                        not:desc:retain
$ hledger is -Y -f 2022-closed.journal                                        not:desc:retain
$ hledger is -Y -f 2023.journal                                               # unclosed file, no query needed
```