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doc: clarify csv rules application order

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Dmitry Astapov 2019-10-15 23:38:23 +01:00
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hledger-lib/hledger_csv.m4.md
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@ -292,6 +292,37 @@ This will generate a [balance assertion](journal.html#balance-assertions)
(or if the amount is left empty, a [balance assignment](journal.html#balance-assignments)),
on the appropriate posting, whenever the running balance field is non-empty.
## References to other fields and evaluation order
Field assignments could include references to other fields or even to the same field you are trying to assign:
```
fields date,description,currency,amount1
amount1 %amount1 USD
amount1 %amount1 EUR
amount1 %amount1 %currency
if SOME_REGEXP
amount1 %amount1 GBP
```
This is how this file would be evaluated.
First, parts of CVS record are assigned according to `fields` directive.
Then all other field assignments -- written at top level, or included in `if` blocks -- are considered to see if they should be applied. They are checked in the order they are written, with later assignment overwriting earlier ones.
Once full set of field assignments that should be applied is known, their values are computed, and this is when all `%<fieldname>` references are evaluated.
So for a particular row from CSV file, value from fourth column would be assigned to `amount1`.
Then `hledger` will decide that `amount1` would have to be amended to `%amount1 USD`, but this will not happen immediately. This choice would be replaced by decision to rewrite `amount1` to `%amount EUR`, which will in turn be thrown away in favor of `%amount1 %currency`. If the `if` block condition will match the row, it will assign `amount1` to `%amount1 GBP`.
Overall, we will end up with one of the two alternatives for `amount1` - either `%amount1 %currency` or `%amount1 GBP`.
Now substitution of all referenced values will happen, using the current values for `%amount1` and `currency`, which were provided by the `fields` directive.
## Reading multiple CSV files
You can read multiple CSV files at once using multiple `-f` arguments on the command line,