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### 8.14.14 Regular Expression matching and substituting

The following listing contains the interface of the RegEx unit.

This unit provides routines to match strings against regular expressions and perform substitutions using matched subexpressions. Regular expressions are strings with some characters having special meanings. They describe (match) a class of strings. They are similar to wild cards used in file name matching, but much more powerful.

To use this unit, you will need the ``rx'` library which can be found in http://www.gnu-pascal.de/libs/.

    {$nested-comments}

    { Regular expression matching and replacement

      The RegEx unit provides routines to match strings against regular
      expressions and perform substitutions using matched
      subexpressions.

      To use the RegEx unit, you will need the rx library which can be
      found in http://www.gnu-pascal.de/libs/

      Regular expressions are strings with some characters having
      special meanings. They describe (match) a class of strings. They
      are similar to wild cards used in file name matching, but much
      more powerful.

      There are two kinds of regular expressions supported by this unit,
      basic and extended regular expressions. The difference between
      them is not functionality, but only syntax. The following is a
      short overview of regular expressions. For a more thorough
      explanation see the literature, or the documentation of the rx
      library, or man pages of programs like grep(1) and sed(1).

      Basic           Extended        Meaning
      `.'             `.'             matches any single character
      `[aei-z]'       `[aei-z]'       matches either `a', `e', or any
                                      character from `i' to `z'
      `[^aei-z]'      `[^aei-z]'      matches any character but `a',
                                      `e', or `i' .. `z'
                                      To include in such a list the the
                                      characters `]', `^', or `-', put
                                      them first, anywhere but first, or
                                      first or last, resp.
      `[[:alnum:]]'   `[[:alnum:]]'   matches any alphanumeric character
      `[^[:digit:]]'  `[^[:digit:]]'  matches anything but a digit
      `[a[:space:]]'  `[a[:space:]]'  matches the letter `a' or a space
                                      character (space, tab)
      ...                             (there are more classes available)
      `\w'            `\w'            = [[:alnum:]]
      `\W'            `\W'            = [^[:alnum:]]
      `^'             `^'             matches the empty string at the
                                      beginning of a line
      `$'             `$'             matches the empty string at the
                                      end of a line
      `*'             `*'             matches zero or more occurences of
                                      the preceding expression
      `\+'            `+'             matches one or more occurences of
                                      the preceding expression
      `\?'            `?'             matches zero or one occurence of
                                      the preceding expression
      `\{N\}'         `{N}'           matches exactly N occurences of
                                      the preceding expression (N is an
                                      integer number)
      `\{M,N\}'       `{M,N}'         matches M to N occurences of the
                                      preceding expression (M and N are
                                      integer numbers, M <= N)
      `AB'            `AB'            matches A followed by B (A and B
                                      are regular expressions)
      `A\|B'          `A|B'           matches A or B (A and B are
                                      regular expressions)
      `\( \)'         `( )'           forms a subexpression, to override
                                      precedence, and for subexpression
                                      references
      `\7'            `\7'            matches the 7'th parenthesized
                                      subexpression (counted by their
                                      start in the regex), where 7 is a
                                      number from 1 to 9 ;-).
                                      *Please note:* using this feature
                                      can be *very* slow or take very
                                      much memory (exponential time and
                                      space in the worst case, if you
                                      know what that means ...).
      `\'             `\'             quotes the following character if
                                      it's special (i.e. listed above)
      rest            rest            any other character matches itself

      Precedence, from highest to lowest:
      * parentheses (`()')
      * repetition (`*', `+', `?', `{}')
      * concatenation
      * alternation (`|')

      When performing substitutions using matched subexpressions of a
      regular expression (see `ReplaceSubExpressionReferences'), the
      replacement string can reference the whole matched expression with
      `&' or `\0', the 7th subexpression with `\7' (just like in the
      regex itself, but using it in replacements is not slow), and the
      7th subexpression converted to upper/lower case with `\u7' or
      `\l7', resp. (which also works for the whole matched expression
      with `\u0' or `\l0'). A verbatim `&' or `\' can be specified with
      `\&' or `\\', resp.

      Copyright (C) 1998-2002 Free Software Foundation, Inc.

      Author: Frank Heckenbach <frank@pascal.gnu.de>

      This file is part of GNU Pascal.

      GNU Pascal is free software; you can redistribute it and/or modify
      it under the terms of the GNU General Public License as published
      by the Free Software Foundation; either version 2, or (at your
      option) any later version.

      GNU Pascal is distributed in the hope that it will be useful, but
      WITHOUT ANY WARRANTY; without even the implied warranty of
      MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the GNU
      General Public License for more details.

      You should have received a copy of the GNU General Public License
      along with GNU Pascal; see the file COPYING. If not, write to the
      Free Software Foundation, 59 Temple Place - Suite 330, Boston, MA
      02111-1307, USA.

      As a special exception, if you link this file with files compiled
      with a GNU compiler to produce an executable, this does not cause
      the resulting executable to be covered by the GNU General Public
      License. This exception does not however invalidate any other
      reasons why the executable file might be covered by the GNU
      General Public License.

      Please also note the license of the rx library. }

    {$gnu-pascal,I-}
    {$if __GPC_RELEASE__ < 20000412}
    {$error This unit requires GPC release 20000412 or newer.}
    {$endif}

    unit RegEx;

    interface

    uses GPC;

    const
      { `BasicRegExSpecialChars' contains all characters that have
        special meanings in basic regular expressions.
        `ExtRegExSpecialChars' contains those that have special meanings
        in extended regular expressions. }
      BasicRegExSpecialChars = ['.', '[', ']', '^', '$', '*', '\'];
      ExtRegExSpecialChars   =
      ['.', '[', ']', '^', '$', '*', '+', '?', '{', '}', '|', '(', ')', '\'];

    type
      { The type used by the routines of the `RegEx' unit to store
        regular expressions in an internal format. The fields RegEx,
        RegMatch, ErrorInternal, From and Length are only used
        internally. SubExpressions can be read after `NewRegEx' and will
        contain the number of parenthesized subexpressions. Error should
        be checked after `NewRegEx'. It will be `nil' when it succeeded,
        and contain an error message otherwise. }
      RegExType = record
        RegEx, RegMatch: Pointer;  { Internal }
        ErrorInternal: CString;    { Internal }
        From, Length: Integer;     { Internal }
        SubExpressions: Integer;
        Error: PString
      end;

    { Simple interface to regular expression matching. Matches a regular
      expression against a string starting from a specified position.
      Returns the position of the first match, or 0 if it does not
      match, or the regular expression is invalid. }
    function  RegExPosFrom (const Expression: String; ExtendedRegEx,
      CaseInsensitive: Boolean; const s: String; From: Integer):
      Integer; asmname '_p_regexposfrom';

    { Creates the internal format of a regular expression. If
      ExtendedRegEx is True, Expression is assumed to denote an extended
      regular expression, otherwise a basic regular expression.
      CaseInsensitive determines if the case of letters will be ignored
      when matching the expression. If NewLines is True, `NewLine'
      characters in a string matched against the expression will be
      treated as dividing the string in multiple lines, so that `$' can
      match before the NewLine and `^' can match after. Also, `.' and
      `[^...]' will not match a NewLine then. }
    procedure NewRegEx (var RegEx: RegExType; const Expression: String;
      ExtendedRegEx, CaseInsensitive, NewLines: Boolean);
      asmname '_p_newregex';

    { Disposes of a regular expression created with `NewRegEx'. *Must*
      be used after `NewRegEx' before the RegEx variable becomes invalid
      (i.e., goes out of scope or a pointer pointing to it is Dispose'd
      of). }
    procedure DisposeRegEx (var RegEx: RegExType);
      asmname '_p_dispose_regex';

    { Matches a regular expression created with `NewRegEx' against a
      string. }
    function  MatchRegEx (var RegEx: RegExType; const s: String;
      NotBeginningOfLine, NotEndOfLine: Boolean): Boolean;
      asmname '_p_matchregex';

    { Matches a regular expression created with `NewRegEx' against a
      string, starting from a specified position. }
    function  MatchRegExFrom (var RegEx: RegExType; const s: String;
      NotBeginningOfLine, NotEndOfLine: Boolean; From: Integer):
      Boolean; asmname '_p_matchregexfrom';

    { Finds out where the regular expression matched, if `MatchRegEx' or
      `MatchRegExFrom' were successful. If n = 0, it returns the
      position of the whole match, otherwise the position of the n'th
      parenthesized subexpression. MatchPosition and MatchLength will
      contain the position (counted from 1) and length of the match, or
      0 if it didn't match. (Note: MatchLength can also be 0 for a
      successful empty match, so check whether MatchPosition is 0 to
      find out if it matched at all.) MatchPosition or MatchLength may
      be Null and is ignored then. }
    procedure GetMatchRegEx (var RegEx: RegExType; n: Integer; var
      MatchPosition, MatchLength: Integer); asmname '_p_getmatch_regex';

    { Checks if the string s contains any quoted characters or
      (sub)expression references to the regular expression RegEx created
      with `NewRegEx'. These are `&' or `\0' for the whole matched
      expression (if OnlySub is not set) and `\1' .. `\9' for the n'th
      parenthesized subexpression. Returns 0 if it does not contain any,
      and the number of references and quoted characters if it does. If
      an invalid reference (i.e. a number bigger than the number of
      subexpressions in RegEx) is found, it returns the negative value
      of the (first) invalid reference. }
    function  FindSubExpressionReferences (var RegEx: RegExType; const
      s: String; OnlySub: Boolean): Integer;
      asmname '_p_find_subexpressionreferences_regex';

    { Replaces (sub)expression references in ReplaceStr by the actual
      (sub)expressions and unquotes quoted characters. To be used after
      the regular expression RegEx created with `NewRegEx' was matched
      against s successfully with `MatchRegEx' or `MatchRegExFrom'. }
    function  ReplaceSubExpressionReferences (var RegEx: RegExType;
      const s, ReplaceStr: String): TString;
      asmname '_p_replace_subexpressionreferences_regex';

    { Returns the string for a regular expression that matches exactly
      one character out of the given set. It can be combined with the
      usual operators to form more complex expressions. }
    function  CharSet2RegEx (const Characters: CharSet): TString;
      asmname '_p_CharSet2RegEx';

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