There are abbreviations, called shorthands, for often needed character sets:

  • [digit] or [d] matches a decimal number. It is similar to ['0'-'9'], except that it is Unicode aware.

  • [word] or [w] matches a word character, i.e. a letter, digit or underscore. It’s similar to ['0'-'9' 'a'-'z' 'A'-'Z' '_'], except that it is Unicode aware. It matches all codepoints in the Alphabetic, Mark, Decimal_Number, Connector_Punctuation, and Join_Control Unicode categories.

  • [space] or [s] matches whitespace. It is equivalent to the White_Space category.

  • [horiz_space] or [h] matches horizontal whitespace, e.g. tabs und spaces.

  • [vert_space] or [v] matches vertical whitespace, e.g. line breaks.

These can be combined as well:

[d s '.']   # match digits, spaces, and dots

Note that word, digit and space only match ASCII characters, if the regex engine isn’t configured to be Unicode-aware. How to enable Unicode support is described here.

What if I don’t need Unicode?

You don’t have to use Unicode-aware character sets such as [digit] if you know that the input is only ASCII. Unicode-aware matching can be considerably slower. For example, the [word] character class includes more than 100,000 code points, so matching a [ascii_word] (which includes only 63 code points) is faster.

Pomsky supports a number of ASCII-only shorthands:

Character classEquivalent
[ascii_alpha]['a'-'z' 'A'-'Z']
[ascii_alnum]['0'-'9' 'a'-'z' 'A'-'Z']
[ascii_blank][' ' U+09],
[ascii_cntrl][U+00-U+1F U+7F]
[ascii_print][' '-'~']
[ascii_punct]['!'-'/' ':'-'@' '['-'`' '{'-'~']
[ascii_space][' ' U+09-U+0D]
[ascii_word]['0'-'9' 'a'-'z' 'A'-'Z' '_']
[ascii_xdigit]['0'-'9' 'a'-'f' 'A'-'F']

Using them can improve performance, but be careful when you use them. If you aren’t sure if the input will ever contain non-ASCII characters, it’s better to err on the side of correctness, and use Unicode-aware character classes.

Non-printable characters

Characters that can’t be printed should be replaced with their hexadecimal Unicode code point. For example, you may write U+FEFF to match the Zero Width No-Break Space.

There are also 6 non-printable characters with a name:

  • [n] matches the \n line feed.
  • [r] matches the \r carriage return.
  • [f] matches the \f form feed.
  • [a] matches the “alert” or “bell” control character.
  • [e] matches the “escape” control character.

Other characters have to be written in their hexadecimal form:

[U+10-U+30 U+FEFF]

Note that you don’t need to write leading zeroes, i.e. U+0 is just as ok as U+0000. However, it is conventional to write ASCII characters with two digits and non-ASCII characters with 4, 5 or 6 digits depending on their length.