Regular Expressions
Regular expressions are a particular kind of formal grammar used to parse strings and other textual information that are known as Regular Languages in formal language theory.
Index
Syntax
| Delimiters | |
|---|---|
^ |
Start. |
$ |
End. |
/x/ |
Start and end. |
| Character Classes | |
|---|---|
\d |
Digit. |
\w |
Word. |
\s |
Whitespace, tab or line break characters. |
\D ^\d |
Not digit. |
\W ^\w |
Not word. |
\S ^\s |
Not whitespace, tab or line break characters. |
. |
Any character. |
| Composites | |
|---|---|
xy |
x followed by y. |
x|y |
x or y (prefer x). |
| Quantifiers | |
|---|---|
x? |
0 or 1 (prefer 1). |
x+ |
1 or more (prefer more). |
x* |
0 or more (prefer more). |
x?? |
0 or 1 (prefer 0). |
x+? |
1 or more (prefer fewer). |
x*? |
0 or more (prefer fewer). |
x{n} |
n. |
x{n,m} |
n to m (prefer more). |
x{n,} |
n or more (prefer more). |
x{n}? |
n. |
x{n,m}? |
n to m (prefer fewer). |
x{n,}? |
n or more (prefer fewer). |
| Ranges | |
|---|---|
a-z |
Character in range a-z. |
A-Z |
Character in range A-Z. |
0-9 |
Digit in range 0-9. |
| Flags | |
|---|---|
/x/g |
Global, find all matches rather than stopping after the first match. |
/x/m |
Multi line, ^ and $ match the start and end of a line. |
/x/i |
Case insensitive. |
Characters ^.[$()|*+? can be used with a backslash \.
Examples
Begins with "The".
^The
Ends with "end".
end$
ab followed by zero or one c.
abc?
ab followed by one or more c.
abc+
ab followed by zero or more c.
abc*
ab followed by two c.
abc{2}
ab followed by two up to five c.
abc{2,5}
ab followed by two or more c.
abc{2,}
a followed by b or c.
a(b|c)
a followed by zero or more bc.
a(bc)*
a followed by two up to five bc.
a(bc){2,5}
A string that doesn't contain characters from a to z or from A to Z.
[^a-zA-Z]
A string that doesn't contain the character -.
[^-]
A string that doesn't contain the characters <>.
[^<>]
A string that can be empty.
^(^$)|(<OTHER_REGEXP>)$