a-z matches an lower case letters from a to z
0-5 matches any number from 0 to 5
[] Match exactly one of the objects inside these brackets
[a] matches the letter a
[abc] matches a single letter which can be a, b or c
[a-z] matches any single lower case letter of the alphabet.
() Groups different matches for return purposes
{} Multiplier for repeated copies of pattern defined before it
[a]{2} matches two consecutive lower case letter a: aa
[a]{1,3} matches at least one and up to three lower case letter a, aa, aaa
+ Match at least one, or more, of the pattern defined before it
a+ will match consecutive a's a, aa, aaa, and so on
? Match zero or one of the pattern defined before it
Pattern may or may not be present but can only be matched one time.
[a-z]? matches empty string or any single lower case letter.
* Match zero or more of the pattern defined before it
Wildcard for pattern that may or may not be present.
[a-z]* matches empty string or string of lower case letters.
. Matches any character except newline \n
a. Matches a two character string starting with a and ending with anything except \n
a|b means either a or b can be matched.
red|white|orange matches exactly one of the colors.
[^0-9] character can not contain a number
[^aA] character can not be lower case a or upper case A
\ Escapes special character that follows (overrides above behavior)
^ Match must occur at start of string
^a First character must be lower case letter a
^[0-9] First character must be a number.
$ match must occur at end of string
a$ Last character must be lower case letter a
| order |
name |
representation |
| 1 |
parentheses |
( ) |
| 2 |
multipliers |
? + * {m,n} {m, n}? |
| 3 |
sequence & anchors |
abc ^ $ |
| 4 |
alternation |
| |
Predefined character abbreviations
| abbreviation |
equal to |
meaning |
| \d |
[0-9] |
any single digit |
| \D |
[^0-9] |
any single character that's not a digit |
| \w |
[a-zA-Z0-9_] |
any word character |
| \W |
[^a-zA-Z0-9_] |
any non-word character |
| \s |
[ \r\t\n\f] |
any space character |
| \S |
[^ \r\t\n\f] |
any non-space character |
| \n |
[\n] |
new line |
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