I get it even though Regex is incredibly useful, it is extremely hard to master! This is a cheat sheet that provides the most common RegEx use cases that will help you whenever need a sneak peek at the Regex syntax!
Characters
| Characters | Legend | Example | Sample Match |
|---|---|---|---|
| [abc], [a-c] | Match the given characters/range of characters | abc[abc] | abca, abcb, abcc |
| [^abc], [^a-c] | Negate and match the given characters/range of characters | abc[^abc] | abcd, abce, abc1, ... |
| . | Any character except line break | bc. | bca, bcd, bc1, b., ... |
| \d | Any numeric character (equivalent to [0-9]) | c\d | c1, c2, c3 ... |
| \D | Any non-numeric character (equivalent to [^0-9]) | c\D | ca, c., c* ... |
| \w | Any alphanumeric character (equivalent to [A-Za-z0-9_]) | a\w | aa, a1, a_ ... |
| \W | Any non-alphanumeric character (equivalent to [A-Za-z0-9_]) | a\W | a), a$, a? ... |
| \s | Usually used for white space, but can be used for new line, tab, etc | a\s | a |
| \S | Not a white space or equivalent like new line, tab, etc | a\S | aa |
| \t | Matches a horizontal tab | T\tab | T ab |
| \r | Matches a carriage return | AB\r\nCD | AB CD |
| \n | Matches a linefeed | AB\r\nCD | AB CD |
| \ | Escapes special characters | \d | 0, 1, ... |
| x|y | Matches either "x" or "y" | a|b | a, b |
Assertions
| Characters | Legend | Example | Sample Match |
|---|---|---|---|
| ^ | Start of string or start of line depending on multiline mode | ^abc.* | abc, abd, abcd, ... |
| $ | End of string or start of line depending on multiline mode | .*xyz$ | xyz, wxyz, abcdxyz, ... |
| \b | Matches a word character is not followed by another word-character | My.*\bpie | My apple pie, ... |
| \B | Matches a non-word boundary | c.*\Bcat | copycat, ... |
| x(?=y) | Lookahead assertion: Matches "x" only if "x" is followed by "y" | \d+(?=€) | $1 = 0.98€, ... |
| x(?!y) | Negative Lookahead assertion: Matches "x" only if "x" is followed not by "y" | \d+\b(?!€) | $1 = 0.98€ , ... |
| (?<=y)x | Lookbehind assertion: Matches "x" only if "x" is preceded by "y" | (?<=\d)\d | $1 = 0.9*8*€, ... |
| (?<!y)x | Negative Lookbehind assertion: Matches "x" only if "x" is not preceded by "y" | (?<!\d)\d | $1 = 0.98€, ... |
Groups
| Characters | Legend | Example | Sample Match |
|---|---|---|---|
| (x) | Capturing group: Matches x and remembers the match | A(nt|pple) | Ant (remembers "nt") |
| (?<name>x) | Capturing group: Matches x and stores it in the mentioned variable | A(?<m>nt|pple) | Ant (m = "nt") |
| (?:name>x) | Non-capturing group: Matches x and does not remember the match | A(?:nt|pple) | Ant |
| \n | Back reference to the last substring matching the n parenthetical | (\d)+(\d)=\2+\1 | 5+6=6+5 |
Quantifiers
| Characters | Legend | Example | Sample Match |
|---|---|---|---|
| x* | Matches the preceding item "x" 0 or more times | a* | a, aa, aaa, ... |
| x+ | Matches the preceding item "x" 1 or more times, equivalent to {1,} | a+ | aa, aaa, aaaa, ... |
| x? | Matches the preceding item "x" 0 or 1 time | ab? | a, ab |
| x{n} | Matches the preceding item "x" n times (n = positive integer) | ab{5}c | abbbbbc |
| x{n,} | Matches the preceding item "x" at least n times (n = positive integer) | ab{2,}c | abbc, abbbc, abbbbc, ... |
| x{n,m} | Matches the preceding item "x" at least n times & at most m times (n<m) | ab{2,3}c | abbc, abbbc |
NOTE
By default quantifiers are greedy (they try to match as much of the string as possible). The ? character after the quantifier makes the quantifier non-greedy (it will stop as soon as it finds a match).
For Example: \d+? for a test string 12345 will match only 1, but \d+ will match the entire string 12345
Flags
Flags are put at the end of the regular expression. They are used to modify how the regular expression behaves.
For Example: /a/ for a test string a will match a only, but adding the flag i (/a/i) would match both a and A
| Characters | Legend |
|---|---|
| d | Generate indices for substring matches |
| g | Global search |
| i | Case-insensitive search |
| m | Multi-line search |
| s | Allows . to match newline characters
|
| u | Treats a pattern as a sequence of Unicode code points |
| y | Perform a sticky search that matches starting at the current position in the target string |
That's all folks!
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FAQ
These are a few commonly asked questions I get. So, I hope this FAQ section solves your issues.
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I am a beginner, how should I learn Front-End Web Dev?
Look into the following articles: Would you mentor me?
Sorry, I am already under a lot of workload and would not have the time to mentor anyone.
Top comments (14)
Most useful image I ever downloaded:
Abeg where you download this
As usual, I feel compelled to point out that you don't need most of these things and you don't want most of these things.
Especially readahead and lookbehind are features that add needless complexity and performance drawbacks (given an ideal implementation of the underlying algorithm).
My rule of thumb is usually: If you can't express it using exclusively concatenation, union, alternation, Kleene star, groups, and anchors, it probably shouldn't be done with regex.
This also ties into how I try to explain regex to people: A lot of the symbols are just shorthands for other symbol combinations:
a+is the same asaa*.a?is the same asa|. Technically, even[ab]is justa|b. It's obviously a lot easier to write the shorthands - but the actual feature set you really need and want can all be boiled down into^(|)*$and that's wonderful. (Named and non-matching groups notwithstanding, of course.)Hello Tapajyoti Bose,
thank you for your article.
I think I'll find it useful when I start working with regex again, as I'm no real expert.
I especially like how you added an example with a sample match for better understanding.
Thanks for sharing this list.
Normally, I never know how to regex. Just opening regexr.com and try different patterns.
Nice work, and of course the required XKCD: xkcd.com/208/
As a corollary, the inimitable Jeff Atwood: blog.codinghorror.com/regular-expr...
😄
very well written with examples, thank you
I like Regex 101 because it has all of that information right where you can write and test your regex.
Thanks for providing this
Woww, niice!
Nice