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102 lines
2.8 KiB
Markdown
102 lines
2.8 KiB
Markdown
---
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title: findRESubmatch
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description: Returns a slice of all successive matches of the regular expression. Each element is a slice of strings holding the text of the leftmost match of the regular expression and the matches, if any, of its subexpressions.
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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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- "findRESubmatch PATTERN INPUT [LIMIT]"
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- "strings.FindRESubmatch PATTERN INPUT [LIMIT]"
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relatedfuncs: [findRE, replaceRE]
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---
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By default, `findRESubmatch` finds all matches. You can limit the number of matches with an optional LIMIT parameter. A return value of nil indicates no match.
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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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[string literal]: https://go.dev/ref/spec#String_literals
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This function uses the [RE2] regular expression library. See the [RE2 syntax documentation] for details. Note that the RE2 `\C` escape sequence is not supported.
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[RE2]: https://github.com/google/re2/
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[RE2 syntax documentation]: https://github.com/google/re2/wiki/Syntax/
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{{% note %}}
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The RE2 syntax is a subset of that accepted by [PCRE], roughly speaking, and with various [caveats].
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[caveats]: https://swtch.com/~rsc/regexp/regexp3.html#caveats
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[PCRE]: https://www.pcre.org/
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{{% /note %}}
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## Demonstrative examples
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```go-html-template
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{{ findRESubmatch `a(x*)b` "-ab-" }} → [["ab" ""]]
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{{ findRESubmatch `a(x*)b` "-axxb-" }} → [["axxb" "xx"]]
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{{ findRESubmatch `a(x*)b` "-ab-axb-" }} → [["ab" ""] ["axb" "x"]]
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{{ findRESubmatch `a(x*)b` "-axxb-ab-" }} → [["axxb" "xx"] ["ab" ""]]
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{{ findRESubmatch `a(x*)b` "-axxb-ab-" 1 }} → [["axxb" "xx"]]
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```
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## Practical example
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This markdown:
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```text
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- [Example](https://example.org)
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- [Hugo](https://gohugo.io)
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```
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Produces this HTML:
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```html
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<ul>
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<li><a href="https://example.org">Example</a></li>
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<li><a href="https://gohugo.io">Hugo</a></li>
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</ul>
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```
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To match the anchor elements, capturing the link destination and text:
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```go-html-template
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{{ $regex := `<a\s*href="(.+?)">(.+?)</a>` }}
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{{ $matches := findRESubmatch $regex .Content }}
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```
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Viewed as JSON, the data structure of `$matches` in the code above is:
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```json
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[
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[
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"<a href=\"https://example.org\"></a>Example</a>",
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"https://example.org",
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"Example"
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],
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[
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"<a href=\"https://gohugo.io\">Hugo</a>",
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"https://gohugo.io",
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"Hugo"
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]
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]
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```
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To render the `href` attributes:
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```go-html-template
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{{ range $matches }}
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{{ index . 1 }}
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{{ end }}
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```
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Result:
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```text
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https://example.org
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https://gohugo.io
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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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