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60 lines
2 KiB
Markdown
60 lines
2 KiB
Markdown
---
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title: findRE
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description: Returns a slice of strings that match the regular expression.
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categories: [functions]
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menu:
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docs:
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parent: functions
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keywords: [regex]
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signature:
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- "findRE PATTERN INPUT [LIMIT]"
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- "strings.FindRE PATTERN INPUT [LIMIT]"
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relatedfuncs: [replaceRE]
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aliases: []
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---
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By default, the `findRE` function finds all matches. You can limit the number of matches with an optional LIMIT parameter.
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When specifying the regular expression, use a raw [string literal] (backticks) instead of an interpreted string literal (double quotes) to simplify the syntax. With an interpreted string literal you must escape backslashes.
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The syntax of the regular expression is the same general syntax used by Perl, Python, and other languages. More precisely, it is the syntax accepted by [RE2] except for `\C`.
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This example returns a slice of all second level headings (`h2` elements) within the rendered `.Content`:
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```go-html-template
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{{ findRE `(?s)<h2.*?>.*?</h2>` .Content }}
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```
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The `s` flag causes `.` to match `\n` as well, allowing us to find an `h2` element that contains newlines.
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To limit the number of matches to one:
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```go-html-template
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{{ findRE `(?s)<h2.*?>.*?</h2>` .Content 1 }}
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```
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{{% note %}}
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You can write and test your regular expression using [regex101.com](https://regex101.com/). Be sure to select the Go flavor before you begin.
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{{% /note %}}
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## findRESubmatch
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In Hugo 0.110.0 we added a variant of `findRe` that returns a slice of strings holding the text of the leftmost match of the regular expression in s and the matches, if any, of its subexpressions.
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This:
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```go-html-template
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{{ findRESubmatch §§<a\s*href="(.+?)">(.+?)</a>§§ §§<li><a href="#foo">Foo</a></li> <li><a href="#bar">Bar</a></li>§§ | print | safeHTML }}
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```
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Will print:
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```
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[[<a href=\"#foo\">Foo</a> #foo Foo] [<a href=\"#bar\">Bar</a> #bar Bar]]
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```
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{{< new-in "0.110.0" >}}
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[RE2]: https://github.com/google/re2/wiki/Syntax
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[string literal]: https://go.dev/ref/spec#String_literals
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