Medium - Regex tutorial — A quick cheatsheet by examples
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Trend 파악을 Medium 기고문 요약 포스팅 - 정규식 예제;
Basic topics
Anchors - ^ and $
^The matches any string that starts with The -> Try it!
end$ matches a string that ends with end
^The end$ exact string match (starts and ends with The end)
roar matches any string that has the text roar in it
Quantifiers - *+? and {}
abc* matches a string that has ab followed by zero or more c -> Try it!
abc+ matches a string that has ab followed by one or more c
abc? matches a string that has ab followed by zero or one c
abc{2} matches a string that has ab followed by 2 c
abc{2,} matches a string that has ab followed by 2 or more c
abc{2,5} matches a string that has ab followed by 2 up to 5 c
a(bc)* matches a string that has a followed by zero or more copies of the sequence bc
a(bc){2,5} matches a string that has a followed by 2 up to 5 copies of the sequence bc
OR operator - | or []
a(b|c) matches a string that has a followed by b or c -> Try it!
a[bc] same as previous
Character classes - \d \w \s and .
\d matches a single character that is a digit -> Try it!
\w matches a word character (alphanumeric character plus underscore) -> Try it!
\s matches a whitespace character (includes tabs and line breaks)
. matches any character -> Try it!
\D matches a single non-digit character -> Try it!
\$\d matches a string that has a $ before one digit -> Try it!
Flags
Intermediate topics
Grouping and capturing - ()
a(bc) parentheses create a capturing group with value bc -> Try it!
a(?:bc)* using ?: we disable the capturing group -> Try it!
a(?<foo>bc) using ?<foo> we put a name to the group -> Try it!
Bracket expressions - []
[abc] matches a string that has either an a or a b or a c -> is the same as a|b|c -> Try it!
[a-c] same as previous
[a-fA-F0-9] a string that represents a single hexadecimal digit, case insensitively -> Try it!
[0-9]% a string that has a character from 0 to 9 before a % sign
[^a-zA-Z] a string that has not a letter from a to z or from A to Z.
In this case the ^ is used as negation of the expression -> Try it!
Greedy and Lazy match
<.+?> matches any character one or more times included
inside < and >, expanding as needed -> Try it!
<[^<>]+> matches any character except < or > one or more times included inside < and > -> Try it!
Advanced topics
Boundaries - \b and \B
\babc\b performs a "whole words only" search -> Try it!
\Babc\B matches only if the pattern is fully surrounded by word characters -> Try it!
Back-references - \1
([abc])\1 using \1 it matches the same text that was matched by the first capturing group -> Try it!
([abc])([de])\2\1 we can use \2 (\3, \4, etc.) to identify the same text that was
matched by the second (third, fourth, etc.) capturing group -> Try it!
(?<foo>[abc])\k<foo> we put the name foo to the group and we reference it later (\k<foo>).
The result is the same of the first regex -> Try it!
Look-ahead and Look-behind - (?=) and (?<=)
d(?=r) matches a d only if is followed by r, but r will not be part of the overall regex match -> Try it!
(?<=r)d matches a d only if is preceded by an r, but r will not be part of the overall regex match -> Try it!
d(?!r) matches a d only if is not followed by r, but r will not be part of the overall regex match -> Try it!
(?<!r)d matches a d only if is not preceded by an r, but r will not be part of the overall regex match -> Try it!
