Cheatography
https://cheatography.com
Anchors (boundaries)
^ |
Start of string or line |
$ |
End of string or line |
\A |
Start of input (ignores 'm' flag) |
\Z |
End of input (ignores 'm' flag) |
\G |
End of the previous match |
\b |
Word boundary (any position proceeded or followed - but not both - by a letter, digit or underscore) |
\B |
Non-word boundary |
Character and Sets
\w |
Word |
[a-zA-Z0-9_] |
\W |
Non-word |
[^a-zA-Z0-9_] |
\d |
Digit |
[0-9] |
\D |
Non-digit |
\s |
Whitespace (Form-feed, tab, vertical-tab, new line, carriage return and space) |
[\f\t\x0b\n\r ] |
\S |
Non-whitespace |
\x |
Hexadecimal digit |
\x00=null; \x0d=\r; [\x61-\x7a]=[a-z] |
\O |
Octal digit |
. |
Any character (except new line \n) |
Groups
(...) |
Capture group - captures a set of characters for a later expression |
(?:...) |
Non-capture group - groups an expression but does not capture. e.g. /((?:foo|fu)bar)/ matches "foobar" or "fubar" without "foo" or "fu" appearing as a captured subpattern |
(?=...) |
Lookahead - match on the characters following. e.g. /ab(?=c)/ match "ab" only when followed by "c" |
(?!...) |
Negative lookahead - match on characters that aren't following. e.g. /ab(?!c)/ match "ab" only when NOT followed by "c" |
(?<=...) |
Positive look-behind assertion. e.g. /(?<=foo)bar/ matches "bar" when preceded by "foo" |
(?<!...) |
Negative look-behind assertion. e.g. /(?<!foo)bar/ - matches "bar" when not preceded by "foo" |
(?#...) |
Comment e.g. (?# This comment is ignored entirely) |
Unicode character support
\x0000-\xFFFF |
Unicode hexadecimal character set |
\x00-\xFF |
ASCII hexadecimal character set |
\cA-\cZ |
Control characters |
Unicode is not fully supported on all platforms. JavaScript prior to ES6 for example allows ASCII hex but not full Unicode hex.
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Special Characters
\n |
New line |
\r |
Carriage return |
\t |
Tab |
\v |
Vertical tab |
\f |
Form feed |
Quantifiers
* |
Zero or more |
+ |
One or more |
? |
Zero or One (i.e. optional) |
{n} |
Exactly 'n' (any number) |
{n,} |
Minimum ('n' or more) |
{n,m} |
Range ('n' or more, but less or equal to 'm') |
Flags (expression modifiers)
/m |
Milti-line. (Makes ^ and $ match the start and end of a line respectively) |
/s |
Treat input as a single line. (Makes '.' match new lines as well) |
/i |
Case insensitive pattern matching. |
/g |
Global matching. (Don't stop after first match in a replacement function) |
/x |
Extended matching. (disregard white-space not explicitly escaped, and allow comments starting with #) |
Escape Characters
In regular expressions, the following characters have special meaning and must be escaped: ^ $ [ { ( ) < > . * \ + | ?
Additionally the hyphen (-) and close square bracket (]) must be escaped when in an expression set ( [...]
).
e.g. /\(\d{3}\) \d{4}[\- ]\d{4}/
matches "(nnn) nnnn-nnnn" or "(nnn) nnnn nnnn" (where n is a numeric digit). |
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Comments
Greetings, and thanks for providing this.
Where can I find a comprehensive, accessible textual reference on this topic that includes numerous examples? Instead of pursuing blind trial and error, I would like to understand thoroughly what I am doing, and why.
Thanks.
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