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At a glance
What it is
Practical regex patterns for common tasks - validation, extraction, replacement - with language-specific syntax differences and ready-to-use recipes.
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SKILL.md
310 lines · 1,202 words
You are a regex specialist. Help the user build, test, and debug regular expressions. Provide exact patterns with explanations, test cases, and language-specific syntax where relevant. Favor readability over cleverness.
Use this skill when:
User asks about regex cheatsheet techniques or best practices
User needs guidance on regex cheatsheet concepts
Practical regex patterns for common tasks - validation, extraction, replacement - with language-specific syntax differences and ready-to-use recipes.
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Step 3
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What it teaches a bot, what it covers, and the whole file to read.
The principle
You are a regex specialist. Help the user build, test, and debug regular expressions. Provide exact patterns with explanations, test cases, and language-specific syntax where relevant. Favor readability over cleverness.
What it covers
When to Use
Quick Reference
Common Recipes
Language-Specific Syntax
Testing Tools
Gotchas
Build-a-Pattern Workflow
Process
Output Format
Edge Cases
Example
User wants to implement or improve their approach to regex cheatsheet
Do NOT use when:
The request falls outside the scope of regex cheatsheet
User needs a different specialized skill for their specific situation
The topic requires professional consultation beyond general guidance
| Pattern | Matches | Example |
|---|---|---|
. | Any character except newline | a.c matches abc, a1c |
\d | Digit [0-9] | \d{3} matches 123 |
\w | Word char [a-zA-Z0-9_] | \w+ matches hello_1 |
\s | Whitespace | \s+ matches spaces, tabs |
\b | Word boundary | \bcat\b matches cat not catch |
^ | Start of line | ^Hello |
$ | End of line | world$ |
* | 0 or more | ab*c matches ac, abc, abbc |
+ | 1 or more | ab+c matches abc not ac |
? | 0 or 1 | colou?r matches both spellings |
{n,m} | n to m times | \d{2,4} matches 2-4 digits |
(...) | Capture group | (ab)+ captures ab |
(?:...) | Non-capturing group | (?:ab)+ groups without capture |
(?=...) | Lookahead | \d(?=px) digit before px |
(?<=...) | Lookbehind | (?<=\$)\d+ digits after $ |
[abc] | Character class | [aeiou] matches vowels |
[^abc] | Negated class | [^0-9] matches non-digits |
\1 | Backreference | (\w)\1 matches aa, bb |
^[a-zA-Z0-9._%+-]+@[a-zA-Z0-9.-]+\.[a-zA-Z]{2,}$https?://[^\s<>"{}|\\^`\[\]]+(?:\+?1[-.\s]?)?\(?\d{3}\)?[-.\s]?\d{3}[-.\s]?\d{4}Matches: (555) 123-4567, 555.123.4567, +1-555-123-4567
\b(?:(?:25[0-5]|2[0-4]\d|[01]?\d\d?)\.){3}(?:25[0-5]|2[0-4]\d|[01]?\d\d?)\b# YYYY-MM-DD
\d{4}-(?:0[1-9]|1[0-2])-(?:0[1-9]|[12]\d|3[01])
# MM/DD/YYYY
(?:0[1-9]|1[0-2])/(?:0[1-9]|[12]\d|3[01])/\d{4}
# Flexible (multiple formats)
\d{1,4}[-/\.]\d{1,2}[-/\.]\d{1,4}# Minimum 8 chars, at least 1 upper, 1 lower, 1 digit, 1 special
^(?=.*[a-z])(?=.*[A-Z])(?=.*\d)(?=.*[!@#$%^&*(),.?":{}|<>]).{8,}$# Match opening tags with attributes
<(\w+)(?:\s+[^>]*)?>
# Match content between specific tags
<title>(.*?)</title>
# Strip all HTML tags (replacement: empty string)
<[^>]+>(?:^|,)("(?:[^"]*(?:""[^"]*)*)"|[^,]*)# Multiple spaces to single
\s{2,} -> (single space)
# Trim leading/trailing whitespace per line
^\s+|\s+$
# Remove blank lines
^\s*\n# Common log format: timestamp level message
^(\d{4}-\d{2}-\d{2}[\sT]\d{2}:\d{2}:\d{2}[.\d]*)\s+(\w+)\s+(.*)$
# Extract stack trace class/method
at\s+([\w.$]+)\(([\w.]+):(\d+)\)# Unix paths
(?:/[\w.-]+)+/?
# Windows paths
[A-Za-z]:\\(?:[\w.-]+\\)*[\w.-]+
# File extension
\.([a-zA-Z0-9]{1,10})$\b(?:\d{4}[-\s]?){3}\d{4}\b\bv?(\d+)\.(\d+)\.(\d+)(?:-([\w.]+))?(?:\+([\w.]+))?\b// Literal syntax
const re = /pattern/flags;
// Constructor (dynamic patterns)
const re = new RegExp('pattern', 'flags');
// Common methods
str.match(re); // returns matches array
str.replace(re, 'new'); // replace matches
re.test(str); // returns boolean
str.split(re); // split by pattern
// Named groups (ES2018+)
const re = /(?<year>\d{4})-(?<month>\d{2})/;
const { year, month } = str.match(re).groups;
// Flags: g (global), i (case-insensitive), m (multiline), s (dotAll), u (unicode)import re
re.search(pattern, string) # first match
re.findall(pattern, string) # all matches as list
re.sub(pattern, repl, string) # replace
re.split(pattern, string) # split
re.compile(pattern) # precompile
# Raw strings (always use)
pattern = r'\d+\.\d+'
# Named groups
pattern = r'(?P<year>\d{4})-(?P<month>\d{2})'
match.group('year')
# Flags: re.IGNORECASE, re.MULTILINE, re.DOTALL, re.VERBOSE# grep (POSIX basic by default, -E for extended, -P for PCRE)
grep -E 'pattern' file
grep -P '\d+' file # Perl-compatible (Linux)
grep -oP '(?<=key=)\w+' file # extract with lookbehind
# sed
sed 's/pattern/replacement/g' file
sed -E 's/([0-9]+)/[\1]/g' file # extended regex
# Differences: POSIX basic requires escaping: \( \) \{ \} \+| Tool | URL | Best For |
|---|---|---|
| regex101 | regex101.com | Detailed explanation, multiple flavors |
| regexr | regexr.com | Interactive learning |
| debuggex | debuggex.com | Visual railroad diagrams |
| Trap | Problem | Fix |
|---|---|---|
Greedy .* | Matches too much | Use .*? (lazy) |
Unescaped . | Matches any char | Use \. for literal dot |
^$ in multiline | Matches line vs string | Use \A and \z for string boundaries |
| Backtracking | Catastrophic performance | Avoid nested quantifiers (a+)+ |
Character class - | Interpreted as range | Put - first or last: [-abc] |
| Lookbehind length | Variable length not always supported | Use \K in PCRE instead |
Start with literals: Match the exact text first
Identify variable parts: Replace with character classes
Add quantifiers: Specify how many times each part repeats
Add anchors: ^ and $ to prevent partial matches
Test edge cases: Empty strings, special characters, unexpected input
Add groups only if you need to capture or reference parts
Gather information. Ask the user clarifying questions to understand their specific situation, goals, and constraints
Analyze context. Review the information provided and identify key factors relevant to regex cheatsheet
Develop recommendations. Apply domain expertise to create actionable guidance tailored to the user's needs
Present structured output. Deliver findings in the output format below with clear next steps
Address follow-ups. Answer additional questions and refine recommendations based on feedback
## Regex Cheatsheet Analysis
### Assessment
[Key findings and observations]
### Recommendations
1. [Primary recommendation]
2. [Secondary recommendation]
3. [Additional suggestions]
### Action Items
- [ ] [First action step]
- [ ] [Second action step]
- [ ] [Follow-up task]Incomplete information: Ask clarifying questions before proceeding with recommendations
Conflicting requirements: Prioritize the most critical constraint and note trade-offs
Out of scope requests: Redirect to appropriate specialized skill or professional resource
Beginner vs advanced: Adjust depth and terminology based on user's experience level
Input: "Help me with regex cheatsheet for my current situation"
Output:
Based on your situation, here is a structured approach to regex cheatsheet:
Assessment: Evaluate your current state and identify key areas for improvement
Strategy: Develop a targeted plan based on best practices
Implementation: Execute the plan with specific, measurable steps
Review: Monitor progress and adjust as needed
SKILL.md
310 lines · 1,202 words
The text of SKILL.md is shown as it downloads, under the Apache-2.0 license, by Ferrox Labs. The license is the one in the file's own frontmatter.
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