Definition
Regular expressions are patterns used to match character combinations. Look at the given below table:
Regular Expressions Description
foo.* # Matches any string starting with foo
\d* # Match any number decimal digits
[a-zA-Z]+ # Match a sequence of one or more letters
text Match literal text
. Match any character except newline
^ Match the start of a string
$ Match the end of a string
* Match 0 or more repetitions
+ Match 1 or more repetitions
? Match 0 or 1 repetition
+? Match 1 or more, as few as possible
*? Match 0 or more, as few as possible
{m,n} Match m to n repetitions
{m,n}? Match m to n repetitions, few as possible
[...] Match a set of characters
[^...] Match characters, not in a set
A | B Match A or B (...) Match regex in parenthesis as a group
\number Matches text matched by the previous group
\A Matches start of the string
\b Matches empty string at beginning or end of the word
\B Matches empty string not at begin or end of the word
\d Matches any decimal digit
\D Matches any non-digit
\s Matches any whitespace
\S Matches any non-whitespace
\w Matches any alphanumeric character
\W Matches characters not in
\w \Z Match at end of the string.
\\ Literal backslash