🎰 Regular Expressions

Various useful tools and resources for working with regular expressions.

💡 Tips

• Think about you want to "match" or "search"
• For matching, use ^ and $ to match the beginning and end of the string
  • Be careful with multi-line strings
• Different tools may have different syntax

Characters

Character	RegEx	Notes
Lowercase letter	[a-z]
Uppercase letter	[A-Z]
Letter	[a-zA-Z]
Digit	\d	Equal to [0-9]
Non-digit	\D
Whitespace	\s	Could be space, tab, etc.
Non-whitespace	\S
Word character	\w	Equal to [a-zA-Z0-9_]
Non-word	\W
Word boundary	\b
Non-boundary	\B

Quantifiers

note

In possessive match mode, the regex engine will not backtrack to find a match. This is useful when you know that there is only one possible match. This can be more efficient than greedy or reluctant matching, but more prone to not finding a match.

Quantifiers	RegEx	Notes
More or 0	*	Greedy Match (Prefer more)
More or 1	+	Greedy Match (Prefer more)
1 or 0	?	Greedy Match (Prefer one)
0 or more	*?	Reluctant Match (Prefer 0)
1 or more	+?	Reluctant Match (Prefer 1)
0 or 1	??	Reluctant Match (Prefer 0)
0 or more	*+	Possessive Match
1 or more	++	Possessive Match
1 or 0	?+	Possessive Match
Exactly n	{n}, {n}+, {n}?
At least n	{n,}	Greedy Match (Prefer more)
Between n and m	{n,m}	Greedy Match (Prefer more)
At least n	{n,}?	Reluctant Match (Prefer less)
Between n and m	{n,m}?	Reluctant Match (Prefer less)
At least n	{n,}+	Possessive Match
Between n and m	{n,m}+	Possessive Match

Tools

• regex101
• Debuggex
• RegExr
• Rubular

Snippets

Email

TODO

URL

TODO

Base64 encoded string

^[a-zA-Z0-9+/]*={0,2}$

Semantic Version

^(\d+)\.(\d+)\.(\d+)$

Chinese Characters

[\u4e00-\u9fa5]

🇹🇼 Taiwan Address

This is a WIP, might not be perfect.

^[\u4e00-\u9fa5]+?(縣|市)[\u4e00-\u9fa5]+?(鄉|鎮|市|區)[\u4e00-\u9fa5]+?(路|街|大道)([\u4e00-\u9fa5]+?段)?(\d+?巷)?(\d+?弄)?[\d\-、]+?號(.+?棟)?((B?[\d]+?|G|L)樓)?(之\d+?)?$

🇹🇼 Taiwan Address with Village

^[\u4e00-\u9fa5]+?(縣|市)[\u4e00-\u9fa5]+?(鄉|鎮|市|區)([\u4e00-\u9fa5]+?(村|里))?(\d+?鄰)?[\u4e00-\u9fa5]+?(路|街|大道)([\u4e00-\u9fa5]+?段)?(\d+?巷)?(\d+?弄)?[\d\-、]+?號(.+?棟)?((B?[\d]+?|G|L)樓)?(之\d+?)?$

References

• ICU Regular Expressions