5.7 KiB
Title : Regex.md
Common operators
To define patterns to match, you can use these common operators:
| Operator | Description | Example | Returns |
|---|---|---|---|
| ^ | Matches the beginning of a string | ^abc | abc, abcdef..., abc123 |
| $ | Matches the end of a string | abc$ | my:abc, 123abc, theabc |
| . | Matches any character as a wildcard | a.c | abc, asc, a123c |
| An OR character | abc | ||
| (...) | Captures values in the parentheses | (a)b(c) | a and c |
| [...] | Matches anything within the brackets | [abc] | a, b, or c |
| [a-z] | Matches lowercase characters between a and z | [b-z] | bc, mind, xyz |
| [0-9] | Matches any number values between 0 and 9 | [0-3] | 3201 |
| {x} | The exact number of times to match | (abc){2} | abcabc |
| {x,} | The minimum number of times to match | (abc){2,} | abcabcabc |
| * | Matches anything in the place of the *, or a "greedy" match | ab*c | abc, abbcc, abcdc |
| + | Matches the character before the + one or more times | a+c | ac, aac, aaac |
| ? | Matches the character before the ? zero or one times, or a "non-greedy" match | ab?c | ac, abc |
| / | Escapes the character after the /, or creates an escape sequence | a/bc | a c, with the space matching the /b |
To use an operator's literal character within a pattern, not as regex:
- For a circumflex (^), period (.), open bracket ([), dollar sign ($), open or close parenthesis (() or ()), pipe (|), asterisk (*), plus sign (+), question mark (?), open brace ({), or backslash (), follow it with the escape operator ().
- For an end bracket (]) or end brace (}), make it the first character, with or without an opening ^.
- For a dash (-), make it the first or last character, or the second endpoint of a range.
Tip: All characters within brackets are taken literally, and not as regex operators. For example, [*+?{}.] matches any of the literal characters within the brackets.
Match start or end of string (^ and $)
To match patterns at the beginning or end of the string, use the operators ^ and $ , respectively. For example:
| Example | Matches |
|---|---|
| ^The | Any string that starts with The |
| of despair$ | Any string that ends with of despair |
| ^abc$ | A string that starts and ends with abc—an exact match |
Tip: If neither ^ or $ is used, the pattern matches any string that contains the characters specified. For example, notice—with no ^ or $—returns any string that contains notice.
Match characters (*, +, and ?)
To match patterns based on a specific character, follow the character with the operator *, +, or ?. These operators indicate the number of times the character should occur for a match—zero or more, one or more, or one or zero, respectively. For example:
| Example | Matches |
|---|---|
| ab* | A string that contains a, followed by zero or more bs—ac, abc, or abbc |
| ab+ | A string that contains a, followed by one or more bs—abc or abbc, but not ac |
| ab? | A string that contains a, followed by zero or one bs—ac or abc, but not abc |
| a?b+$ | A string that ends with one or more bs, with or without a preceding a; for example, ab, abb, b, or bb, but not aab or aabb |
Match characters' frequency ({...} or (...))
To match a pattern based on how often a single character occurs, follow it with the number or range of instances, wrapped in braces ({...}) . For example:
| Example | Matches |
|---|---|
| ab{2} | A string that contains a, followed by exactly 2 bs—abb |
| ab{2,} | A string that contains a, followed by at least 2 bs—abb, abbbb, etc. |
| ab{3,5} | A string that contains a, followed by three to five bs—abbb, abbbb, or abbbbb |
Tip: Always specify the first number of a range—{0,2}, not {,2}. Instead of the ranges {0,}{0,}, {1,}, or {0,1}, you can use the operators *, +, or ?, respectively.
To match a pattern based on how often a sequence of characters occurs, wrap it in parentheses ((...)). For example, a(bc){1,5} matches a string that contains a, followed by one to five instances of bc.
Match one of multiple patterns (|)
To match one of multiple patterns—such as this OR that—use the OR operator | . For example:
| Example | Matches |
|---|---|
| hi|hello | A string that contains either hi or hello |
| (b|cd)ef | A string that contains either bef or cdef |
| (a | b)*c | A string that has a sequence of alternating as and bs, ending with c |
Match any character (.)
To represent any character in a pattern to match, use the wildcard operator . . For example:
| Example | Matches |
|---|---|
| a.[0-9] | A string that contains a, followed by any character and a digit |
| ^.{3}$ | Any string of exactly three characters |
Match character position ([...])
To match a pattern based on the position of a character, use brackets ([...]). For example:
| Example | Matches |
|---|---|
| [ab] | A string that contains either a or b; equivalent to a|b |
| [a-d] | A string that contains a lowercase a, b, c, or d; equivalent to a|b|c|d or [abcd] |
| ^[a-zA-Z] | A string that starts with any letter, regardless of case |
| [0-9]% | A string that contains any single digit followed by a percent sign |
| ,[a-zA-Z0-9]$ | A string that ends with a comma followed by any character |
Note: All characters within brackets are taken literally, and not as regex operators. For example, [*+?{}.] matches any of the literal characters within the brackets.
Match unwanted characters ([^...])
To match a pattern that does not contain characters, start the sequence with an ^ operator, and wrap it in brackets. For example, %[^a-zA-z]% matches a string with any non-letter character between two percent signs.
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