212 lines
12 KiB
Markdown
212 lines
12 KiB
Markdown
# Regular Expressions Cheat Sheet
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A regular expression specifies a set of strings that matches it. This cheat sheet is based off Python 3's Regular Expressions (http://docs.python.org/3/library/re.html) but is designed for searches within Sublime Text.
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https://gist.github.com/IsaacCisneros/d7f3cf4bf6c0573d0570
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https://ahkde.github.io/docs/v1/misc/RegEx-QuickRef.htm
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https://serverdiscounter.com/blog/2026-01-26-regex-grundlagen
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## Special Characters
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| :------: | :------------------------------------------------------------------------------ | :------------------------------------------------------------------------ |
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| `\` | Escapet Sonderzeichen oder kennzeichnet eine spezielle Sequenz | |
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| `.` | Entspricht einem beliebigen einzelnen Zeichen mit Ausnahme eines Zeilenumbruchs | |
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| `^` | Matches the start of the string. | |
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| `$` | Matches the end of the string | |
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| `*` | Greedily matches 0 or more repetitions of the preceding RE. | |
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| `*?` | Matches 0 or more repetitions of the preceding RE. | |
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| `+` | Greedily matches 1 or more repetitions of the preceding RE. | |
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| `+?` | Matches 1 or more repetitions of the preceding RE. | |
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| `?` | Greedily matches 0 or 1 repetitions of the preceding RE. | |
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| `??` | Matches 0 or 1 repetitions of the preceding RE. | |
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| `A\|B` | Matches A, if A is unmatched then matches B, where A and B are arbitrary REs. | |
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| `{m}` | Matches exactly m many repetitions of the previous RE. | |
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| `{m,n}` | Greedily matches from m many to n many repetitions of the previous RE. | |
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| `{m,n}?` | Matches m many to n many repetitions of the previous RE. | |
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| `[...]` | Indicates a set of characters to match. | |
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| | `[amk]` | Matches 'a', 'm', or 'k'. |
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| | `[a-z]` | Matches 'a' through 'z'. |
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| | `[a-f0-7]` | Matches 'a' through 'f' or '0' through '7'. |
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| | `[a\-z]` | Matches 'a', '-', or 'z'. |
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| | `[a-]` | Matches 'a' or '-'. |
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| | `[-a]` | Matches 'a' or '-'. |
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| | `[(+*)]` | Matches '(', '+', '*', or ')'. `[]` matches special characters literally. |
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[\w] Matches the character class for '\w'. See character classes.
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[^5] Matches anything other than '5'. '^' forms the complementary set only as the first character in a set.
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[]()] Matches ']', '(', and ')'. ']' is taken literally only as the first character in a set.
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[()\]] Matches ']', '(', and ')'.
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(...) Matches the RE inside the parenthesis and assigns a new group.
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(?P<name>...) The RE matched is accessible by the group indicated by name.
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(?...) Extension notation which changes a RE's behavior. These do not assign a new group.
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(?aiLmsux) Sets the corresponding flag to each letter. Does not work within Sublime Text.
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(?:...) A non-capturing version of parenthesis. The matched substring cannot be retrieved later.
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(?P=name) Matches the substring matched by the group named name.
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(?#...) A comment, the contents are ignored.
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(?=...) Lookahead assertion, the preceding RE only matches if this matches.
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(?!...) Negative lookahead assestion, the preceding RE only matches if this doesn't match.
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(?<=...) Positive lookbehind assertion, the following RE will only match if preceeded with this fixed length RE.
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(?<!...) Negative lookbehind assertion, the following RE will only match if not preceeded with this fixed length RE.
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(?(id)true|false) If group id exists then uses the true RE, else use the false RE.
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> Character classes
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> \1 Matches the contents of the group labelled by the same number. Acceptable numbers are 1-99.
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> \A Matches at the start of the current string.
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> \b Matches the empty string at the beginning or end of a word. \b matches the boundary between \w and \W.
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> \B Matches the empty string not at the beginning or end of a word.
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> \d Matches any Unicode decimal digit, including 0-9.
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> \D Matches any Unicode non-decimal digit.
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> \s Matches any Unicode whitespace character, including ' ', \t, \n, \r, \f and \v.
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> \S Matches any Unicode non-whitespace character.
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> \w Matches any Unicode word character, including a-z, A-Z, and 0-9.
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> \W Matches any Unicode non-word character.
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> \Z Matches at the end of the string.
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\a Matches the ASCII Bell ().
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\f Matches the ASCII Formfeed ( ).
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\n Matches the ASCII Linefeed.
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\r Matches the ASCII Carriage Return (
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).
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\t Matches the ASCII Horizontal Tab.
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\v Matches the ASCII Vertical Tab ( ).
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#########################
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### Regular Expression Cheat Sheet with Examples
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Regular Expressions (regex) are patterns used to match strings in text. Below is a cheat sheet with common regex patterns and examples.
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---
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### **1. Anchors**
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| Pattern | Description | Example | Matches |
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| ------- | ------------------- | -------- | -------------- |
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| `^` | Start of the string | `^Hello` | `Hello world!` |
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| `$` | End of the string | `world$` | `Hello world!` |
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---
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### **2. Quantifiers**
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| Pattern | Description | Example | Matches |
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| ------- | ------------------------------- | --------- | ------------------------ |
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| `*` | 0 or more | `a*` | `aaa`, `b` |
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| `+` | 1 or more | `a+` | `aaa`, but not `b` |
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| `?` | 0 or 1 | `colou?r` | `color`, `colour` |
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| `{n}` | Exactly `n` occurrences | `a{3}` | `aaa`, but not `aa` |
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| `{n,}` | At least `n` occurrences | `a{2,}` | `aa`, `aaa` |
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| `{n,m}` | Between `n` and `m` occurrences | `a{2,3}` | `aa`, `aaa`, but not `a` |
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---
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### **3. Character Classes**
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| Pattern | Description | Example | Matches |
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| ------- | ---------------------------------------- | ------- | --------------- |
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| `.` | Any character except newline | `a.b` | `acb`, `a9b` |
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| `\d` | Any digit (0-9) | `\d+` | `123`, `9` |
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| `\D` | Any non-digit | `\D+` | `abc`, `@#` |
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| `\w` | Any word character (alphanumeric or `_`) | `\w+` | `hello_123` |
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| `\W` | Any non-word character | `\W+` | `@!`, ` #` |
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| `\s` | Any whitespace | `\s+` | ` `, `\t`, `\n` |
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| `\S` | Any non-whitespace | `\S+` | `abc`, `123` |
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---
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### **4. Logical OR and Grouping**
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| Pattern | Description | Example | Matches |
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| ------- | ----------- | ----------------------- | ------- |
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| `a | b` | Match either `a` or `b` | `cat |
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| `(ab | cd)` | Grouping | `(ab |
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---
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### **5. Escape Characters**
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| Pattern | Description | Example | Matches |
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| ------- | ----------- | --------- | ------- |
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| `\.` | Literal dot | `a\.b` | `a.b` |
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| `\[` | Literal `[` | `\[abc\]` | `[abc]` |
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---
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### **6. Ranges**
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| Pattern | Description | Example | Matches |
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| -------------- | --------------------------- | -------- | ------------ |
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| `[a-z]` | Lowercase letters | `[a-z]+` | `abc`, `xyz` |
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| `[A-Z]` | Uppercase letters | `[A-Z]+` | `ABC`, `XYZ` |
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| `[0-9]` | Digits | `[0-9]+` | `123`, `456` |
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| `[a-zA-Z0-9_]` | Alphanumeric and underscore | `\w+` | `hello123_` |
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---
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### **7. Special Sequences**
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| Pattern | Description | Example | Matches |
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| ---------- | ------------------- | ------------- | ----------------- |
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| `(?=...)` | Positive lookahead | `foo(?=bar)` | `foo` in `foobar` |
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| `(?!...)` | Negative lookahead | `foo(?!bar)` | `foo` in `foobaz` |
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| `(?<=...)` | Positive lookbehind | `(?<=foo)bar` | `bar` in `foobar` |
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| `(?<!...)` | Negative lookbehind | `(?<!foo)bar` | `bar` in `bazbar` |
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---
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### **8. Common Patterns**
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| Use Case | Regex | Example |
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| ----------------------- | ------------------------------------------------ | --------------------- |
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| Match email | `[a-zA-Z0-9._%+-]+@[a-zA-Z0-9.-]+\.[a-zA-Z]{2,}` | `user@example.com` |
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| Match URL | `https?://[^\s]+` | `https://example.com` |
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| Match phone number | `\d{3}-\d{3}-\d{4}` | `123-456-7890` |
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| Match date (YYYY-MM-DD) | `\d{4}-\d{2}-\d{2}` | `2024-12-13` |
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---
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### **9. Flags**
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| Flag | Description | Example |
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| ---- | ---------------- | ------------------------------ |
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| `i` | Case-insensitive | `/hello/i` matches `Hello` |
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| `g` | Global match | `/hello/g` matches all `hello` |
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| `m` | Multiline | `/^hello/m` matches per line |
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---
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### **10. Examples in Code**
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#### Python Example:
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```python
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import re
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# Match an email
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pattern = r"[a-zA-Z0-9._%+-]+@[a-zA-Z0-9.-]+\.[a-zA-Z]{2,}"
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email = "contact@example.com"
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print(re.match(pattern, email)) # Output: <re.Match object>
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```
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#### JavaScript Example:
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```javascript
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// Match a URL
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let pattern = /https?:\/\/[^\s]+/g;
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let text = "Visit https://example.com for more info.";
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console.log(text.match(pattern)); // Output: [ 'https://example.com' ]
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```
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[regular-expressions-v2.pdf](regular-expressions-v2.pdf)
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[regular-expressions-cheat-sheet-v1.pdf](regular-expressions-cheat-sheet-v1.pdf)
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[regex-cheatsheet.pdf](regex-cheatsheet.pdf)
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