87 lines
2.6 KiB
Markdown
87 lines
2.6 KiB
Markdown
# Multiline mode of anchors ^ $, flag "m"
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The multiline mode is enabled by the flag `pattern:m`.
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It only affects the behavior of `pattern:^` and `pattern:$`.
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In the multiline mode they match not only at the beginning and the end of the string, but also at start/end of line.
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## Searching at line start ^
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In the example below the text has multiple lines. The pattern `pattern:/^\d/gm` takes a digit from the beginning of each line:
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```js run
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let str = `1st place: Winnie
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2nd place: Piglet
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3rd place: Eeyore`;
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*!*
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console.log( str.match(/^\d/gm) ); // 1, 2, 3
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*/!*
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```
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Without the flag `pattern:m` only the first digit is matched:
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```js run
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let str = `1st place: Winnie
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2nd place: Piglet
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3rd place: Eeyore`;
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*!*
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console.log( str.match(/^\d/g) ); // 1
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*/!*
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```
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That's because by default a caret `pattern:^` only matches at the beginning of the text, and in the multiline mode -- at the start of any line.
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```smart
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"Start of a line" formally means "immediately after a line break": the test `pattern:^` in multiline mode matches at all positions preceded by a newline character `\n`.
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And at the text start.
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```
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## Searching at line end $
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The dollar sign `pattern:$` behaves similarly.
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The regular expression `pattern:\d$` finds the last digit in every line
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```js run
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let str = `Winnie: 1
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Piglet: 2
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Eeyore: 3`;
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console.log( str.match(/\d$/gm) ); // 1,2,3
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```
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Without the flag `pattern:m`, the dollar `pattern:$` would only match the end of the whole text, so only the very last digit would be found.
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```smart
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"End of a line" formally means "immediately before a line break": the test `pattern:$` in multiline mode matches at all positions succeeded by a newline character `\n`.
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And at the text end.
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```
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## Searching for \n instead of ^ $
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To find a newline, we can use not only anchors `pattern:^` and `pattern:$`, but also the newline character `\n`.
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What's the difference? Let's see an example.
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Here we search for `pattern:\d\n` instead of `pattern:\d$`:
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```js run
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let str = `Winnie: 1
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Piglet: 2
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Eeyore: 3`;
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console.log( str.match(/\d\n/gm) ); // 1\n,2\n
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```
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As we can see, there are 2 matches instead of 3.
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That's because there's no newline after `subject:3` (there's text end though, so it matches `pattern:$`).
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Another difference: now every match includes a newline character `match:\n`. Unlike the anchors `pattern:^` `pattern:$`, that only test the condition (start/end of a line), `\n` is a character, so it becomes a part of the result.
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So, a `\n` in the pattern is used when we need newline characters in the result, while anchors are used to find something at the beginning/end of a line.
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