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Last updated September 30, 2022.

Regex pattern matching is supported in most modern programming languages, however they each might have their own regex engine implementing a custom ‘flavour’ of regex.

Use this regex engine comparison table to check if the syntax you’re trying to use is supported.

Use regex101 to sanity check the correctness of your regex pattern.

.Any character.
*0 or more times.
?0 or 1 time.
+1 or more times.
^Match from the start of the string.
$Match up to the end of the string.
{n,m}n (inclusive) to m (inclusive) times.
[a-zA-Z0-9]Alphanumeric characters, lowercase and uppercase.
[^a-zA-Z0-9]Anything apart from alphanumeric characters.
hello|worldMatches hello or world.
hell(o|w)orldMatches helloorld or hellworld. We use parentheses for grouping among other things.
Character ClassDescription
\wAny word, which is basically a shorthand for [a-zA-Z_0-9].
\WAnything not a word.
\dAny digit, which is basically a shorthand for [0-9].
\DAnything not a digit.
\sAny whitespace character (space, tabs, newlines, etc.)
\SAnything not a whitespace.

# Non-Greedy Matching

Regex matching is typically greedy, meaning that (Ha){3,5} will match the longest string possible, which would be HaHaHaHaHa if that exists. Using (Ha){3,5}? will perform non-greedy matching, preferring to match HaHaHa.

You can use non-greedy matching by appending a ? qualifier. For example, .*? matches 0 or more of any character non-greedily.

# Example

Suppose we want to interpolate values into the string: "Hi {{world_type}}. I am {{name}}.". We’d might use the regex: {{(.*)}} and extract out the capture group. Since greedy matching is the default, this would extract the capture group: world_type}}. I am {{name. To fix this, use the regex {{(.*?)}}.