Special characters and character classes Flashcards
0
Q
[…]
A
The bracket expression specifies a character class and matches any single character contained within the brackets or range of characters. Example: [abc] matches a, b and/or c, in any order. A range of characters is specified using the -, for example [a-z] matches any lowercase ASCII letter from a to z. Other examples include [A-F] which matches any uppercase ASCII letter from A to F, and [4-7] which matches any number from 4 to 7. The - character is treated as a literal character if it's listed first, last or escaped: [-] matches -, [a-] matches a and/or -, [a\-z] matches a, - and/or z. Additionally, listed characters can be mixed with ranges of characters. Example: [0-9a-fA-F] matches any number and also letters from a to z irrespective of their case, [02468aeiouy-] matches even numbers, vowels and the - character. Brackets inside bracket expressions are treated as literals if they are escaped. Example: [\[\]] matches [ and/or ]. The [ doesn't need to be escaped if it's listed first: [[] matches [
1
Q
.
A
Matches any single character except the newline character. Example: .at matches bat, cat, rat and also .at, 1at
Equivalent to [^\x0A\x0D\u2028\u2029]
2
Q
[^…]
A
The negated bracket expression or negated character class matches any single character not contained within the brackets or range of characters. Same as above, except that the ^ negates the expression. Example: [0-9] matches any character that's not a number. Although the ^ character is a special character, it doesn't need to be escaped within the brackets in order to be treated as a literal. Example: [^] matches anything, [^^] matches anything except the ^ character.
3
Q
\w
A
Word character
Equivalent to [A-Za-z0-9_]
4
Q
\W
A
Non-word character
Equivalent to [^A-Za-z0-9_]
5
Q
\d
A
Digit character
Equivalent to [0-9]
6
Q
\D
A
Non-digit character
Equivalent to [^0-9]
7
Q
\s
A
Whitespace character
Equivalent to [\f\n\r\t\v\u00A0\u2028\u2029] (\u00A0 means “no-break space”, \u2028 means “line separator”, \u2029 means “paragraph separator”)
8
Q
\S
A
Non-whitespace character
Equivalent to [^\f\n\r\t\v\u00A0\u2028\u2029]
9
Q
\b
A
Word Boundary
Backspace (\x08)
10
Q
\f
A
Form-feed (\x0C)
11
Q
\n
A
Linefeed or newline (\x0A)
12
Q
\r
A
Carriage return (\x0D)
13
Q
\t
A
Tab (\x09)
14
Q
\v
A
Vertical tab (\x0B)
