Regular Expression Enhancements in Epsilon 10

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Epsilon User's Manual and Reference > Changes from Older Versions > Enhanced Features in Epsilon 10 >

Regular Expression Enhancements in Epsilon 10

Previous versions of Epsilon let you write <Tab> or <#9> to represent special characters, or use the syntax <#9|Space|;> to match one of a set of characters. Epsilon now recognizes a few additional names, listed below, that represent predefined sets of characters. Some use Epsilon's current syntax table, which an EEL program may modify, by way of the isalpha( ) primitive. Typically this includes accented characters like ê or å.

Class   Meaning

<digit>   A digit, 0 to 9.

<alpha>   A letter, according to isalpha( ).

<alphanum>   Either of the above.

<word>   All of the above, plus the _ character.

<hspace>   The same as <Space|Tab>.

<wspace>   The same as <Space|Tab|Newline>.

<any>   Any character including <Newline>.

You may mix the above class names with other <> character representations. For example, <^digit|a-f> matches any character except of one these: 0123456789abcdef.

Epsilon also recognizes some new assertions. Like the assertions ^ and $, these don't match any specific characters, but a potential match will be rejected if the assertion is not true at the appropriate point in the match.

Assertion   Meaning

^   At the start of a line.

$   At the end of a line.

<bob> or <bof>   At the start of the buffer.

<eob> or <eof>   At the end of the buffer.

For example, searching for <bob>sometext<eob> won't succeed unless the buffer contains only the eight character string sometext.

You can now create new assertions from character classes specified with the angle bracket syntax by adding [, ] or / at the start of the pattern.

Assertion   Meaning

<[class>   The next character matches class, the previous one does not.

<]class>   The previous character matches class, the next one does not.

</class>   Either of the above.

The class in the above syntax is a |-separated list of one or more single characters, character names like Space or Tab, character numbers like #32 or #9, ranges of any of these, or character class names like Word or Digit.

For example, </word> matches at a word boundary, and <]word> matches at the end of a word. The pattern <]0-9|a-f> matches at the end of a run of hexadecimal digits. And the pattern (cat|[0-9])</digit>(dog|[0-9]) matches cat3 or 4dog, but not catdog or 42.

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