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Answer architecture round 2, stability round 1 and product-owner round 1: a format string on stdin keeps every byte while JSON or a lone reference drops one newline, an operand's error names stdin, a file or the pipe, {//x} is refused and "{/x}" read as its record, plain echo and a heredoc in the examples, goal 7 reads one command line, decision titles drop argument, and items 157 to 159 filed

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Lilleman auf Larv
2026-10-07 17:04:00 +02:00
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@@ -6,41 +6,44 @@ reproducible.
```sh
go install github.com/larvit/fejkdata/cmd/fejkdata@latest
echo -n '{/sv_SE.person}' | fejkdata # Sara Eriksson
echo '{/sv_SE.person}' | fejkdata # Sara Eriksson
```
## CLI
```sh
echo -n '{/sv_SE.person}' | fejkdata # Sara Eriksson
echo -n '{/sv_SE.person.last}' | fejkdata # Eriksson
echo -n '{/sv_SE.person} hihi' | fejkdata # Sara Eriksson hihi
echo -n '{/sv_SE.address}' | fejkdata --seed 42 # the same address every run
echo -n '{/sv_SE.word}' | fejkdata -n 3 --separator ', ' # nät, barn, sol
fejkdata --list # every path the data offers
echo -n '{/misc.territory[SE].capital}' | fejkdata # Stockholm — a table's row, selected by key or name
echo -n '{/geo.SE.locality[Lund].street}' | fejkdata # Fjelievägen — a linked table, drawn inside the row
echo -n '{/sv_SE.word}' | fejkdata --data-path ./mydata # layer a directory over the shipped data
fejkdata --no-shipped-data -d ./mydata --list # only your data
echo -n "{date(1990-01-01,2010-12-31,'2006-01-02')}" | fejkdata # 2003-11-27 — the layout in '…'
echo -n '{"format":"name: {x}","x":["bosse","lina"]}' | fejkdata # name: bosse or name: lina
fejkdata < template.txt # a template kept in a file
echo '{/sv_SE.person}' | fejkdata # Sara Eriksson
echo '{/sv_SE.person.last}' | fejkdata # Eriksson
echo '{/sv_SE.person} hihi' | fejkdata # Sara Eriksson hihi, then echo's newline
echo '{/sv_SE.address}' | fejkdata --seed 42 # the same address every run
echo '{/sv_SE.word}' | fejkdata -n 3 --separator ', ' # nät, barn, sol
fejkdata --list # every path the data offers
echo '{/misc.territory[SE].capital}' | fejkdata # Stockholm — a table's row, selected by key or name
echo '{/geo.SE.locality[Lund].street}' | fejkdata # Fjelievägen — a linked table, drawn inside the row
echo '{/sv_SE.word}' | fejkdata --data-path ./mydata # layer a directory over the shipped data
fejkdata --no-shipped-data -d ./mydata --list # only your data
echo '{"format":"name: {x}","x":["bosse","lina"]}' | fejkdata # name: bosse or name: lina
fejkdata < template.txt # a template kept in a file
fejkdata <<'EOF' # born 2003-11-27 — a quoted heredoc passes ', $ and \ as written
born {date(1990-01-01,2010-12-31,'2006-01-02')}
EOF
```
fejkdata renders the template on its stdin: a format string, or a JSON object, array or
string. Its `{…}` tokens reach the data by reference from the root,
`{/sv_SE.person.last}`, so shipped and `--data-path` categories are alike available,
and everything outside them prints as written. A reference names a category, or a field
and everything outside them prints as written; stdin that is JSON is read as JSON, so
`42`, `true` or `null` alone is refused. A reference names a category, or a field
inside one: each dot segment descends one level — folders, then the category (a JSON
file), then fields — and `[SE]` after a [table](#table) selects its row. `--list` prints
these paths; a template reads one as `{/path}`.
One newline ending stdin, `\n` or `\r\n`, is dropped, so `echo` and `echo -n`, a file
and a heredoc render alike; end stdin with two newlines to print one. Some shells' `echo`
reads a backslash as an escape, so pipe a template holding one with `printf '%s'` or from
a file. One reference alone, `{/users}`, is the record `users` under `--format`; the
rest of stdin's rules are under
[Decisions](docs/decisions.md#the-cli-renders-the-template-on-its-stdin-less-one-newline-ending-it).
A format string keeps every byte of stdin, so `echo`'s newline renders too; `printf '%s'`
leaves it out. A JSON template or one reference alone drops one newline ending stdin,
`\n` or `\r\n`, which neither could print. One reference alone, `{/users}`, is the record
`users` under `--format`. Some shells' `echo` reads a backslash as an escape, so pipe a
template holding one from a quoted heredoc or a file. The rest of stdin's rules are under
[Decisions](docs/decisions.md#the-cli-renders-the-template-on-its-stdin-keeping-a-format-strings-every-byte).
| Flag | |
|------|--|
@@ -57,7 +60,7 @@ rest of stdin's rules are under
`--name value` and `--name=value` both work, a short flag's value attaches or
follows (`-n3`, `-n 3`) and short flags bundle (`-hn 3`) — see
[Decisions](docs/decisions.md#flags-follow-getopt_long); flags go anywhere, `--` ends them. Exit codes: `0` success, `1` runtime error (missing
dir, a lone reference to nothing), `2` misuse — a bad flag, an argument, nothing on stdin, or a
dir, a lone reference to nothing), `2` misuse — a bad flag, an operand, nothing on stdin, or a
template that does not compile. From a checkout:
`go run ./cmd/fejkdata …`.
@@ -78,9 +81,9 @@ A category is a JSON file in a directory. Save this as `mydata/sql.json`:
```
```sh
echo -n '{/sql}' | fejkdata --seed 1 --data-path ./mydata
echo '{/sql}' | fejkdata --seed 1 --data-path ./mydata
# INSERT INTO users VALUES('zoom'),('wahoo'),('blip');
echo -n '{/sql}' | fejkdata --repeat 100 --data-path ./mydata > seed.sql
echo '{/sql}' | fejkdata --repeat 100 --data-path ./mydata > seed.sql
```
That `format` string is the free-form spelling — you hand-write the whole row.
@@ -103,11 +106,11 @@ the whole. `--format json|ndjson|csv|sql` writes the records; the library's
```
```sh
echo -n '{/users}' | fejkdata --seed 1 -d ./mydata --format json # [{"first":"Bo","last":"Lovelace"}]
echo -n '{/users}' | fejkdata --seed 1 -d ./mydata --format ndjson # {"first":"Bo","last":"Lovelace"}
echo -n '{/users}' | fejkdata --seed 1 -d ./mydata --format csv # first,last → Bo,Lovelace
echo -n '{/users}' | fejkdata --seed 1 -d ./mydata --format sql # INSERT INTO "users" ("first", "last") VALUES ('Bo', 'Lovelace');
echo -n '{/users}' | fejkdata --seed 1 -d ./mydata --format sql --table people # INSERT into another table
echo '{/users}' | fejkdata --seed 1 -d ./mydata --format json # [{"first":"Bo","last":"Lovelace"}]
echo '{/users}' | fejkdata --seed 1 -d ./mydata --format ndjson # {"first":"Bo","last":"Lovelace"}
echo '{/users}' | fejkdata --seed 1 -d ./mydata --format csv # first,last → Bo,Lovelace
echo '{/users}' | fejkdata --seed 1 -d ./mydata --format sql # INSERT INTO "users" ("first", "last") VALUES ('Bo', 'Lovelace');
echo '{/users}' | fejkdata --seed 1 -d ./mydata --format sql --table people # INSERT into another table
```
A record is one reference alone, `{/users}`, or a template whose fields are its
@@ -508,11 +511,11 @@ SE Sweden 10500000
```
```sh
echo -n '{/country}' | fejkdata -d ./mydata # Sweden (SE), about half the time
echo -n '{/country.alpha2}' | fejkdata -d ./mydata # NO
echo -n '{/country[SE]}' | fejkdata -d ./mydata # Sweden (SE)
echo -n '{/country[Norway].alpha2}' | fejkdata -d ./mydata # NO
echo -n '{/country}' | fejkdata -d ./mydata --format csv # alpha2,name,population → SE,Sweden,10500000
echo '{/country}' | fejkdata -d ./mydata # Sweden (SE), about half the time
echo '{/country.alpha2}' | fejkdata -d ./mydata # NO
echo '{/country[SE]}' | fejkdata -d ./mydata # Sweden (SE)
echo '{/country[Norway].alpha2}' | fejkdata -d ./mydata # NO
echo '{/country}' | fejkdata -d ./mydata --format csv # alpha2,name,population → SE,Sweden,10500000
```
`rows` names the TSV beside the category file; `key` names the column a path
@@ -568,10 +571,10 @@ Stockholm SE 990000
```
```sh
echo -n '{/country[SE].city}' | fejkdata -d ./mydata # Stockholm or Göteborg
echo -n '{/country.city.name}' | fejkdata -d ./mydata # a country drawn, then a city inside it
echo -n '{/city[Oslo].country}' | fejkdata -d ./mydata # NO — the link column's cell
echo -n '{/city as c}{c.name}, {c..country.name}' | fejkdata -d ./mydata # Oslo, Norway — one city and its country
echo '{/country[SE].city}' | fejkdata -d ./mydata # Stockholm or Göteborg
echo '{/country.city.name}' | fejkdata -d ./mydata # a country drawn, then a city inside it
echo '{/city[Oslo].country}' | fejkdata -d ./mydata # NO — the link column's cell
echo '{/city as c}{c.name}, {c..country.name}' | fejkdata -d ./mydata # Oslo, Norway — one city and its country
```
A path descends from a row to a linked table by name, at any depth, and `--list`
@@ -593,10 +596,10 @@ chain of parents that closes, and a table named like a column of any table above
after the `..`:
```sh
echo -n '{/city[Oslo]..country.name}' | fejkdata -d ./mydata # Norway
echo -n '{/city..country}' | fejkdata -d ./mydata # a city drawn, then its country: Sweden (SE)
echo -n '{/city[Göteborg]..country.city}' | fejkdata -d ./mydata # Stockholm or Göteborg, drawn afresh
echo -n '{/city as c}{c}, {c..country.name}' | fejkdata -d ./mydata # Oslo, Norway
echo '{/city[Oslo]..country.name}' | fejkdata -d ./mydata # Norway
echo '{/city..country}' | fejkdata -d ./mydata # a city drawn, then its country: Sweden (SE)
echo '{/city[Göteborg]..country.city}' | fejkdata -d ./mydata # Stockholm or Göteborg, drawn afresh
echo '{/city as c}{c}, {c..country.name}' | fejkdata -d ./mydata # Oslo, Norway
```
It steps up from a selected row, a drawn row or a [name](#names) bound to a row, one
@@ -922,7 +925,7 @@ Where the project is heading; the sections before Audience document what ships t
fails to load instead.
2. Data that reads something nobody provided fails to load, and the error names the
module that provides it by default, or says that none does.
7. **One command gets you a value.**
7. **One command line gets you a value.**
1. Flags work like in other command-line tools, and can go anywhere on the line.
2. Your first template of your own needs no escaping and no options.
3. The CLI fills in what you leave out with a sane default: all the shipped data, the