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292 lines
10 KiB
Markdown
292 lines
10 KiB
Markdown
# String Formatting
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Format strings in gallery-dl follow the general rules of [`str.format()`](https://docs.python.org/3/library/string.html#format-string-syntax) ([PEP 3101](https://www.python.org/dev/peps/pep-3101/)) plus several extras.
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The syntax for replacement fields is `{<field-name>!<conversion>:<format-specifiers>}`, where `!<conversion>` and `:<format-specifiers>` are both optional and can be used to specify how the value selected by `<field-name>` should be transformed.
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## Field Names
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Field names select the metadata value to use in a replacement field.
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While simple names are usually enough, more complex forms like accessing values by attribute, element index, or slicing are also supported.
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| | Example | Result |
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| -------------------- | ----------------- | ---------------------- |
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| Name | `{title}` | `Hello World` |
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| Element Index | `{title[6]}` | `W` |
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| Slicing | `{title[3:8]}` | `lo Wo` |
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| Alternatives | `{empty\|title}` | `Hello World` |
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| Element Access | `{user[name]}` | `John Doe` |
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| Attribute Access | `{extractor.url}` | `https://example.org/` |
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All of these methods can be combined as needed.
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For example `{title[24]|empty|extractor.url[15:-1]}` would result in `.org`.
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## Conversions
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Conversion specifiers allow to *convert* the value to a different form or type. Such a specifier must only consist of 1 character. gallery-dl supports the default three (`s`, `r`, `a`) as well as several others:
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<table>
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<thead>
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<tr>
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<th>Conversion</th>
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<th>Description</th>
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<th>Example</th>
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<th>Result</th>
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</tr>
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</thead>
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<tbody>
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<tr>
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<td align="center"><code>l</code></td>
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<td>Convert a string to lowercase</td>
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<td><code>{foo!l}</code></td>
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<td><code>foo bar</code></td>
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</tr>
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<tr>
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<td align="center"><code>u</code></td>
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<td>Convert a string to uppercase</td>
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<td><code>{foo!u}</code></td>
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<td><code>FOO BAR</code></td>
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</tr>
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<tr>
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<td align="center"><code>c</code></td>
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<td>Capitalize a string, i.e. convert the first character to uppercase and all others to lowercase</td>
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<td><code>{foo!c}</code></td>
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<td><code>Foo bar</code></td>
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</tr>
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<tr>
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<td align="center"><code>C</code></td>
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<td>Capitalize each word in a string</td>
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<td><code>{foo!C}</code></td>
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<td><code>Foo Bar</code></td>
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</tr>
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<tr>
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<td align="center"><code>g</code></td>
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<td>Slugify a value</td>
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<td><code>{foo!g}</code></td>
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<td><code>foo-bar</code></td>
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</tr>
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<tr>
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<td align="center"><code>j</code></td>
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<td>Serialize value to a JSON formatted string</td>
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<td><code>{tags!j}</code></td>
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<td><code>["sun", "tree", "water"]</code></td>
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</tr>
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<tr>
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<td align="center"><code>t</code></td>
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<td>Trim a string, i.e. remove leading and trailing whitespace characters</td>
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<td><code>{bar!t}</code></td>
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<td><code>FooBar</code></td>
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</tr>
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<tr>
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<td align="center"><code>T</code></td>
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<td>Convert a <code>datetime</code> object to a unix timestamp</td>
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<td><code>{date!T}</code></td>
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<td><code>1262304000</code></td>
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</tr>
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<tr>
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<td align="center"><code>d</code></td>
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<td>Convert a unix timestamp to a <code>datetime</code> object</td>
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<td><code>{created!d}</code></td>
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<td><code>2010-01-01 00:00:00</code></td>
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</tr>
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<tr>
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<td align="center"><code>s</code></td>
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<td>Convert value to <a href="https://docs.python.org/3/library/stdtypes.html#text-sequence-type-str" rel="nofollow"><code>str</code></a></td>
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<td><code>{tags!s}</code></td>
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<td><code>['sun', 'tree', 'water']</code></td>
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</tr>
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<tr>
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<td align="center"><code>S</code></td>
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<td>Convert value to <code>str</code> while providing a human-readable representation for lists</td>
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<td><code>{tags!S}</code></td>
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<td><code>sun, tree, water</code></td>
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</tr>
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<tr>
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<td align="center"><code>r</code></td>
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<td>Convert value to <code>str</code> using <a href="https://docs.python.org/3/library/functions.html#repr" rel="nofollow"><code>repr()</code></a></td>
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<td></td>
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<td></td>
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</tr>
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<tr>
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<td align="center"><code>a</code></td>
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<td>Convert value to <code>str</code> using <a href="https://docs.python.org/3/library/functions.html#ascii" rel="nofollow"><code>ascii()</code></a></td>
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<td></td>
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<td></td>
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</tr>
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</tbody>
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</table>
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## Format Specifiers
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Format specifiers can be used for advanced formatting by using the options provided by Python (see [Format Specification Mini-Language](https://docs.python.org/3/library/string.html#format-specification-mini-language)) like zero-filling a number (`{num:>03}`) or formatting a [`datetime`](https://docs.python.org/3/library/datetime.html#datetime.datetime) object (`{date:%Y%m%d}`), or with gallery-dl's extra formatting specifiers:
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<table>
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<thead>
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<tr>
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<th>Format Specifier</th>
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<th>Description</th>
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<th>Example</th>
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<th>Result</th>
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</tr>
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</thead>
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<tbody>
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<tr>
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<td rowspan="2"><code>?<start>/<end>/</code></td>
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<td rowspan="2">Adds <code><start></code> and <code><end></code> to the actual value if it evaluates to <code>True</code>. Otherwise the whole replacement field becomes an empty string.</td>
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<td><code>{foo:?[/]/}</code></td>
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<td><code>[Foo Bar]</code></td>
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</tr>
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<tr>
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<td><code>{empty:?[/]/}</code></td>
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<td><code></code></td>
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</tr>
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<tr>
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<td><code>[<start>:<stop>]</code></td>
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<td>Applies a <a href="https://python-reference.readthedocs.io/en/latest/docs/brackets/slicing.html">Slicing</a> operation to the current value, similar to <a href="#field-names">Field Names</a></td>
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<td><code>{foo:[1:-1]}</code></td>
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<td><code>oo Ba</code></td>
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</tr>
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<tr>
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<td rowspan="2"><code>L<maxlen>/<repl>/</code></td>
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<td rowspan="2">Replaces the entire output with <code><repl></code> if its length exceeds <code><maxlen></code></td>
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<td><code>{foo:L15/long/}</code></td>
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<td><code>Foo Bar</code></td>
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</tr>
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<tr>
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<td><code>{foo:L3/long/}</code></td>
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<td><code>long</code></td>
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</tr>
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<tr>
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<td><code>J<separator>/</code></td>
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<td>Concatenates elements of a list with <code><separator></code> using <a href="https://docs.python.org/3/library/stdtypes.html#str.join" rel="nofollow"><code>str.join()</code></a></td>
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<td><code>{tags:J - /}</code></td>
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<td><code>sun - tree - water</code></td>
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</tr>
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<tr>
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<td><code>R<old>/<new>/</code></td>
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<td>Replaces all occurrences of <code><old></code> with <code><new></code> using <a href="https://docs.python.org/3/library/stdtypes.html#str.replace" rel="nofollow"><code>str.replace()</code></a></td>
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<td><code>{foo:Ro/()/}</code></td>
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<td><code>F()() Bar</code></td>
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</tr>
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<tr>
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<td><code>S<order>/</code></td>
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<td>Sort a list. <code><order></code> can be either <strong>a</strong>scending or <strong>d</strong>escending/<strong>r</strong>everse. (default: <strong>a</strong>)</td>
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<td><code>{tags:Sd}</code></td>
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<td><code>['water', 'tree', 'sun']</code></td>
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</tr>
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<tr>
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<td><code>D<format>/</code></td>
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<td>Parse a string value to a <code>datetime</code> object according to <a href="https://docs.python.org/3/library/datetime.html#strftime-and-strptime-format-codes"><code><format></code></a></td>
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<td><code>{updated:D%b %d %Y %I:%M %p/}</code></td>
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<td><code>2010-01-01 00:00:00</code></td>
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</tr>
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<tr>
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<td><code>O<offset>/</code></td>
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<td>Apply <code><offset></code> to a <code>datetime</code> object, either as <code>±HH:MM</code> or <code>local</code> for local UTC offset</td>
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<td><code>{date:O-06:30/}</code></td>
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<td><code>2009-12-31 17:30:00</code></td>
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</tr>
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</tbody>
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</table>
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All special format specifiers (`?`, `L`, `J`, `R`, `D`, `O`) can be chained and combined with one another, but must always come before any standard format specifiers:
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For example `{foo:?//RF/B/Ro/e/> 10}` -> ` Bee Bar`
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- `?//` - Tests if `foo` has a value
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- `RF/B/` - Replaces `F` with `B`
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- `Ro/e/` - Replaces `o` with `e`
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- `> 10` - Left-fills the string with spaces until it is 10 characters long
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## Global Replacement Fields
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Replacement field names that are available in all format strings.
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<table>
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<thead>
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<tr>
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<th>Field Name</th>
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<th>Description</th>
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<th>Example</th>
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<th>Result</th>
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</tr>
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</thead>
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<tbody>
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<tr>
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<td><code>_env</code></td>
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<td>Environment variables</td>
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<td><code>{_env[HOME]}</code></td>
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<td><code>/home/john</code></td>
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</tr>
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<tr>
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<td><code>_now</code></td>
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<td>Current local date and time</td>
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<td><code>{_now:%Y-%m}</code></td>
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<td><code>2022-08</code></td>
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</tr>
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<tr>
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<td rowspan="2"><code>_lit</code></td>
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<td rowspan="2">String literals</td>
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<td><code>{_lit[foo]}</code></td>
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<td><code>foo</code></td>
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</tr>
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<tr>
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<td><code>{'bar'}</code></td>
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<td><code>bar</code></td>
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</tr>
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</tbody>
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</table>
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## Special Type Format Strings
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Starting a format string with '\f<Type> ' allows to set a different format string type than the default. Available ones are:
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<table>
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<thead>
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<tr>
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<th>Type</th>
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<th>Description</th>
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<th width="32%">Usage</th>
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</tr>
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</thead>
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<tbody>
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<tr>
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<td align="center"><code>T</code></td>
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<td>A template file containing the actual format string</td>
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<td><code>\fT ~/.templates/booru.txt</code></td>
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</tr>
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<tr>
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<td align="center"><code>F</code></td>
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<td>An <a href="https://docs.python.org/3/tutorial/inputoutput.html#formatted-string-literals">f-string</a> literal</td>
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<td><code>\fF '{title.strip()}' by {artist.capitalize()}</code></td>
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</tr>
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<tr>
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<td align="center"><code>E</code></td>
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<td>An arbitrary Python expression</td>
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<td><code>\fE title.upper().replace(' ', '-')</code></td>
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</tr>
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<tr>
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<td align="center"><code>M</code></td>
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<td> Name of a Python module followed by one of its functions.
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This function gets called with the current metadata dict as
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argument and should return a string.</td>
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<td><code>\fM my_module:generate_text</code></td>
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</tr>
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</tbody>
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</table>
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> **Note:**
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>
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> `\f` is the [Form Feed](https://en.wikipedia.org/w/index.php?title=Page_break&oldid=1027475805#Form_feed)
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> character. (ASCII code 12 or 0xc)
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> Writing it as `\f` is native to JSON, but will *not* get interpreted
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> as such by most shells. To use this character there:
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> * hold `Ctrl`, then press `v` followed by `l`, resulting in `^L` or
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> * use `echo` or `printf` (e.g. `gallery-dl -f "$(echo -ne \\fM) my_module:generate_text"`)
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