matching symbols

Regular Expression Description

. Matches any character

^regex -> Finds regex that must match at the beginning of the line.

regex$ -> Finds regex that must match at the end of the line.

[abc] -> Set definition, can match the letter a or b or c.

[abc][vz] -> Set definition, can match a or b or c followed by either v or z.

[^abc] -> When a caret appears as the first character inside square brackets, it negates the pattern. This can match any character except a or b or c.

[a-d1-7] -> Ranges: matches a letter between a and d and figures from 1 to 7, but not d1.

X|Z -> Finds X or Z.

XZ -> Finds X directly followed by Z.

$ -> Checks if a line end follows.

Metacharacters

Regular Expression Description

\d -> Any digit, short for [0-9]

\D -> A non-digit, short for [^0-9]

\s -> A whitespace character, short for [ \t\n\x0b\r\f]

\S -> A non-whitespace character, short for [^\s]

\w -> A word character, short for [a-zA-Z_0-9]

\W -> A non-word character [^\w]

\S+ -> Several non-whitespace characters

\b -> Matches a word boundary where a word character is [a-zA-Z0-9_].

Quantifier

Regular Expression Description Examples

• -> Occurs zero or more times, is short for {0,} Examples:X finds no or several letter X,. finds any character sequence

• -> Occurs one or more times, is short for {1,} Examples:X+ - Finds one or several letter X

? -> Occurs no or one times, ? is short for {0,1}. Examples:X? finds no or exactly one letter X

{X} -> Occurs X number of times, {} describes the order of the preceding liberal Examples:\d{3} searches for three digits, .{10} for any character sequence of length 10.

{X,Y} -> Occurs between X and Y times, Examples:\d{1,4} means \d must occur at least once and at a maximum of four.

*? -> ? after a quantifier makes it a reluctant quantifier. It tries to find the smallest match.