02. Matching Characters and Digits

One digit

Match any digit from 0 to 9 using \d.

To match any non-digit, use the upper-case \D.

One character

Use the dot (.). This will match any character - a letter, digit or whitespace. To use the actual period scape with a backslash \..

One alphanumeric character

Any alphanumeric character including the underscore. Use \w. As you'll learn soon, this is the same as [a-zA-Z0-9_].

Any non-alphanumeric character is \W. This is helpful especially for matching punctuations.

Boundary between word and non-word

\b matches the boundary between a word and a non-word character.

Matching one from set of characters

Place each character within square brackets.

[abc]
Match a, b or c.

Excluding matches to set of specific characters

Use the square brackets, just like above, with a hat (^) inside of it.

[^abc]
Match any character except for a, b or c.

Range between two letters or two digits

There is a shortcut to specifying any range of letters or digits. Instead of writing [abcdefghijklmnopqrstuvwxyz] we can just write write the range between two letter or numbers, separated by a dash (-).

[0-4]
Matches digits from 0 to 4.
[a-z]
All lowercase letters from a to z.
[A-Z]
All uppercase letters from A to Z.

Whitespace

The whitespace special character \s will match single type of whitespace - a space, tab, newline or carriage return.

To specify any number of whitespace character use the \s*.

Any non-whitespace character will be \S.

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