mirror of
https://github.com/CorentinTh/it-tools.git
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122 lines
3.2 KiB
Markdown
122 lines
3.2 KiB
Markdown
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### Normal characters
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Expression | Description
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:--|:--
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`.` or `[^\n\r]` | any character *excluding* a newline or carriage return
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`[A-Za-z]` | alphabet
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`[a-z]` | lowercase alphabet
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`[A-Z]` | uppercase alphabet
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`\d` or `[0-9]` | digit
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`\D` or `[^0-9]` | non-digit
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`_` | underscore
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`\w` or `[A-Za-z0-9_]` | alphabet, digit or underscore
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`\W` or `[^A-Za-z0-9_]` | inverse of `\w`
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`\S` | inverse of `\s`
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### Whitespace characters
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Expression | Description
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:--|:--
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` ` | space
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`\t` | tab
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`\n` | newline
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`\r` | carriage return
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`\s` | space, tab, newline or carriage return
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### Character set
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Expression | Description
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:--|:--
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`[xyz]` | either `x`, `y` or `z`
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`[^xyz]` | neither `x`, `y` nor `z`
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`[1-3]` | either `1`, `2` or `3`
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`[^1-3]` | neither `1`, `2` nor `3`
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- Think of a character set as an `OR` operation on the single characters that are enclosed between the square brackets.
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- Use `^` after the opening `[` to “negate” the character set.
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- Within a character set, `.` means a literal period.
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### Characters that require escaping
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#### Outside a character set
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Expression | Description
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:--|:--
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`\.` | period
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`\^` | caret
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`\$` | dollar sign
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`\|` | pipe
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`\\` | back slash
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`\/` | forward slash
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`\(` | opening bracket
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`\)` | closing bracket
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`\[` | opening square bracket
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`\]` | closing square bracket
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`\{` | opening curly bracket
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`\}` | closing curly bracket
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#### Inside a character set
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Expression | Description
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:--|:--
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`\\` | back slash
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`\]` | closing square bracket
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- A `^` must be escaped only if it occurs immediately after the opening `[` of the character set.
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- A `-` must be escaped only if it occurs between two alphabets or two digits.
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### Quantifiers
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Expression | Description
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:--|:--
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`{2}` | exactly 2
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`{2,}` | at least 2
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`{2,7}` | at least 2 but no more than 7
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`*` | 0 or more
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`+` | 1 or more
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`?` | exactly 0 or 1
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- The quantifier goes *after* the expression to be quantified.
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### Boundaries
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Expression | Description
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:--|:--
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`^` | start of string
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`$` | end of string
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`\b` | word boundary
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- How word boundary matching works:
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- At the beginning of the string if the first character is `\w`.
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- Between two adjacent characters within the string, if the first character is `\w` and the second character is `\W`.
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- At the end of the string if the last character is `\w`.
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### Matching
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Expression | Description
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:--|:--
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`foo\|bar` | match either `foo` or `bar`
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`foo(?=bar)` | match `foo` if it’s before `bar`
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`foo(?!bar)` | match `foo` if it’s *not* before `bar`
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`(?<=bar)foo` | match `foo` if it’s after `bar`
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`(?<!bar)foo` | match `foo` if it’s *not* after `bar`
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### Grouping and capturing
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Expression | Description
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:--|:--
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`(foo)` | capturing group; match and capture `foo`
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`(?:foo)` | non-capturing group; match `foo` but *without* capturing `foo`
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`(foo)bar\1` | `\1` is a backreference to the 1st capturing group; match `foobarfoo`
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- Capturing groups are only relevant in the following methods:
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- `string.match(regexp)`
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- `string.matchAll(regexp)`
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- `string.replace(regexp, callback)`
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- `\N` is a backreference to the `Nth` capturing group. Capturing groups are numbered starting from 1.
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## References and tools
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- [MDN](https://developer.mozilla.org/en-US/docs/Web/JavaScript/Guide/Regular_Expressions)
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- [RegExplained](https://leaverou.github.io/regexplained/)
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