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.
| Metacharacter | Description |
|---|---|
. | 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|world | Matches hello or world. |
| hell(o|w)orld | Matches helloorld or hellworld. We use parentheses for grouping among other things. |
| Character Class | Description |
|---|---|
\w | Any word, which is basically a shorthand for [a-zA-Z_0-9]. |
\W | Anything not a word. |
\d | Any digit, which is basically a shorthand for [0-9]. |
\D | Anything not a digit. |
\s | Any whitespace character (space, tabs, newlines, etc.) |
\S | Anything 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 {{(.*?)}}.