Regular expressions with pdfTeX

Question

How can one use \pdfmatch with regular expressions and where can one find a listing and description of all the available pdfTeX primitives and help on their use?

Edit

The latest issue of the pdfTeX documentation, now contains a small description with examples for the command.

Answer 1

See pdftex 1.30.0 announcement, in particular:

  - \pdfmatch [icase] [subcount <number>}] {<pattern>}{<string>}
    Implements pattern matching using the POSIX regex.
    It returns the same values as \pdfstrcmp, but with the following
    semantics: 
      -1: error case (invalid pattern, ...)
       0: no match
       1: match found
    Options:
    * icase: case insensitive matching
    * subcount: it sets the table size for found subpatterns.
      A number "-1" resets the table size to the start default.
  - \pdflastmatch <number>
    The result of \pdfmatch is stored in an array. The entry "0" contains
    the match, the following entries submatches. The positions of the
    matches are also available. They are encoded:
      <position> "->" <match string>
    The position "-1" with an empty string indicates that this entry is not
    set.

Answer 2

For regular expressions specifically, the l3regex package provides a cross-engine solution (needs eTeX and \strcmp).

For instance,

\RequirePackage{l3regex}
\ExplSyntaxOn
\regex_extract_all:nnN { \w+ } { Hello,~ world! } \l_foo_seq
\seq_show:N \l_foo_seq

shows Hello and world as the two items of the resulting sequence (list).

Here's a list of various questions of whose one answer uses l3regex

• Replace characters in string based on preceding and following character
• Substituting strings only when not bounded by letters or numbers
• Extract the numerical and non-numerical portion from text