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;import, print: better deduplication docs

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Simon Michael 2021-02-18 18:35:06 -08:00
parent f7bbb39a77
commit 554f7a59fd
2 changed files with 58 additions and 25 deletions
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63
hledger/Hledger/Cli/Commands/Import.md
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@ -6,19 +6,64 @@ transactions as imported, without actually importing any.
_FLAGS
The input files are specified as arguments - no need to write -f before each one.
So eg to add new transactions from all CSV files to the main journal, it's just:
`hledger import *.csv`
Unlike other hledger commands, with `import` the journal file is an output file,
and will be modified, though only by appending (existing data will not be changed).
The input files are specified as arguments, so to import one or more
CSV files to your main journal, you will run `hledger import bank.csv`
or perhaps `hledger import *.csv`.
New transactions are detected in the same way as print --new:
by assuming transactions are always added to the input files in increasing date order,
and by saving `.latest.FILE` state files.
Note you can import from any file format, though CSV files are the
most common import source, and these docs focus on that case.
The --dry-run output is in journal format, so you can filter it, eg
to see only uncategorised transactions:
### Deduplication
As a convenience `import` does *deduplication* while reading transactions.
This does not mean "ignore transactions that look the same",
but rather "ignore transactions that have been seen before".
This is intended for when you are periodically importing foreign data
which may contain already-imported transactions.
So eg, if every day you download bank CSV files containing redundant data,
you can safely run `hledger import bank.csv` and only new transactions will be imported.
(`import` is idempotent.)
Since the items being read (CSV records, eg) often do not come with
unique identifiers, hledger detects new transactions by date, assuming
that:
1. new items always have the newest dates
2. item dates do not change across reads
3. and items with the same date remain in the same relative order across reads.
These are often true of CSV files representing transactions, or true
enough so that it works pretty well in practice. 1 is important, but
violations of 2 and 3 amongst the old transactions won't matter (and
if you import often, the new transactions will be few, so less likely
to be the ones affected).
hledger remembers the latest date processed in each input file by
saving a hidden ".latest" state file in the same directory. Eg when
reading `finance/bank.csv`, it will look for and update the
`finance/.latest.bank.csv` state file.
The format is simple: one or more lines containing the
same ISO-format date (YYYY-MM-DD), meaning "I have processed
transactions up to this date, and this many of them on that date."
Normally you won't see or manipulate these state files yourself.
But if needed, you can delete them to reset the state (making all
transactions "new"), or you can construct them to "catch up" to a
certain date.
Note deduplication (and updating of state files) can also be done by
[`print --new`](#print), but this is less often used.
### Import testing
With `--dry-run`, the transactions that will be imported are printed
to the terminal, without affecting your journal.
The output is in journal format, so you can re-parse it.
Eg, to see any importable transactions which CSV rules have not categorised:
```shell
$ hledger import --dry ... | hledger -f- print unknown --ignore-assertions
$ hledger import --dry bank.csv | hledger -f- -I print unknown
```
### Importing balance assignments

18
hledger/Hledger/Cli/Commands/Print.md
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@ -79,21 +79,9 @@ With `-m`/`--match` and a STR argument, print will show at most one transaction:
one whose description is most similar to STR, and is most recent. STR should contain at
least two characters. If there is no similar-enough match, no transaction will be shown.
With `--new`, for each FILE being read, hledger reads (and writes) a special
state file (`.latest.FILE` in the same directory), containing the latest transaction date(s)
that were seen last time FILE was read. When this file is found, only transactions
with newer dates (and new transactions on the latest date) are printed.
This is useful for ignoring already-seen entries in import data, such as downloaded CSV files.
Eg:
```shell
$ hledger -f bank1.csv print --new
(shows transactions added since last print --new on this file)
```
This assumes that transactions added to FILE always have same or increasing dates,
and that transactions on the same day do not get reordered.
See also the [import](#import) command.
With `--new`, hledger prints only transactions it has not seen on a previous run.
This uses the same deduplication system as the [`import`](#import) command.
(See import's docs for details.)
This command also supports the
[output destination](hledger.html#output-destination) and