| Pattern |
Description |
. |
Matches any single character except newline |
^ |
Matches the start of a line |
$ |
Matches the end of a line |
* |
Matches 0 or more repetitions of the preceding element |
+ |
Matches 1 or more repetitions of the preceding element |
? |
Makes the preceding element optional (matches 0 or 1 times) |
{n} |
Matches exactly n repetitions of the preceding element |
{n,} |
Matches n or more repetitions of the preceding element |
{n,m} |
Matches between n and m repetitions |
[abc] |
Character set: matches any one of the characters a, b, or c |
[^abc] |
Negated character set: matches any character except a, b, or c |
\d |
Matches any digit character (equivalent to [0-9]) |
\D |
Matches any non-digit character |
\w |
Matches any word character (alphanumeric and underscore) |
\W |
Matches any non-word character |
\s |
Matches any whitespace character (spaces, tabs, line breaks) |
\S |
Matches any non-whitespace character |
(...) |
Capturing group: groups multiple tokens together and captures the match |
(?:...) |
Non-capturing group: groups multiple tokens without capturing |
| |
Alternation: matches either the expression before or after the | (OR operator) |
\b |
Matches a word boundary (the position between a word character and a non-word character) |
\B |
Matches where \b does not, i.e., not a word boundary |
(?=...) |
Positive lookahead: matches a group after the main expression without including it in the result |
(?!...) |
Negative lookahead: specifies a group that can’t match after the main expression |
(?<=...) |
Positive lookbehind: matches a group before the main expression without including it in the result |
(? |
Negative lookbehind: specifies a group that can’t match before the main expression |
\ |
Escape character: used to escape special characters |
| Pattern |
Matches |
^\d{5}$ |
Exactly 5 digits (e.g., US ZIP codes like 12345) |
^\w+@\w+\.\w{2,}$ |
Simple email addresses (e.g., [email protected]) |
^(https?|ftp)://[^\s/$.?#].[^\s]*$ |
URLs starting with http://, https://, or ftp:// |
\b\d{3}-\d{2}-\d{4}\b |
Social Security numbers (e.g., 123-45-6789) |
^\(\d{3}\) \d{3}-\d{4}$ |
US phone numbers in format (123) 456-7890 |
(?i)^[a-z]+$ |
One or more letters (case-insensitive) |
\b\w{4}\b |
Words with exactly 4 letters |
(\d{1,3}\.){3}\d{1,3} |
IP addresses (e.g., 192.168.1.1) |
^[A-Fa-f0-9]{6}$ |
Hex color codes (without #, e.g., FFA07A) |
^\d{4}-\d{2}-\d{2}$ |
Date in format YYYY-MM-DD (e.g., 2023-01-31) |