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To use it, copy files "regexpr.pas", "regexpr_unicodedata.pas", "", to your project folder.

The library is already included into Lazarus (Free Pascal) project so you do not need to copy anything if you use Lazarus.

TRegExpr class

VersionMajor, VersionMinor

Return major and minor version of the component.

VersionMajor = 1
VersionMinor = 101


Regular expression.

For optimization, regular expression is automatically compiled into P-code. Human-readable form of the P-code is returned by Dump.

In case of any errors in compilation, Error method is called (by default Error raises exception ERegExpr).


Set or get values of regular expression modifiers.

Format of the string is similar to (?ismx-ismx). For example ModifierStr := ‘i-x’ will switch on the modifier /i, switch off /x and leave unchanged others.

If you try to set unsupported modifier, Error will be called.


Modifier /i, "case-insensitive", initialized with RegExprModifierI value.


Modifier /r, "Russian range extension", initialized with RegExprModifierR value.


Modifier /s, "single line strings", initialized with RegExprModifierS value.


Modifier /g, "greediness", initialized with RegExprModifierG value.


Modifier /m, "multi-line strings", initialized with RegExprModifierM value.


Modifier /x, "eXtended syntax", initialized with RegExprModifierX value.


Finds regular expression against AInputString, starting from the beginning.

The overloaded Exec version without AInputString exists, it uses AInputString from previous call.

See also global function ExecRegExpr that you can use without explicit TRegExpr object creation.


Finds next match. If parameter ABackward is True, it goes downto position 1, ie runs backward search.

Without parameter it works the same as:

if MatchLen [0] = 0
  then ExecPos (MatchPos [0] + 1)
  else ExecPos (MatchPos [0] + MatchLen [0]);

Raises exception if used without preceeding successful call to Exec, ExecPos or ExecNext.

So you always must use something like:

if Exec(InputString)
      { proceed results}
    until not ExecNext;


Finds match for AInputString starting from AOffset position (1-based).

Parameter ABackward means going from AOffset downto 1, ie backward search.

Parameter ATryOnce means that testing for regex will be only at the initial position, without going to next/previous positions.


Returns current input string (from last Exec call or last assign to this property).

Any assignment to this property clears Match, MatchPos and MatchLen.


function Substitute (const ATemplate : RegExprString) : RegExprString;

Returns ATemplate, where $& or $0 are replaced with the found match, and $1 to $9 are replaced with found groups 1 to 9.

To use in template the characters $ or \, escape them with a backslash \, like \\ or \$.

Symbol Description
$& whole regular expression match
$0 whole regular expression match
$1 .. $9 contents of numbered group 1 .. 9
\n in Windows replaced with \r\n
\l lowercase one next char
\L lowercase all chars after that
\u uppercase one next char
\U uppercase all chars after that
'1\$ is $2\\rub\\' -> '1$ is <Match[2]>\rub\'
'\U$1\\r' transforms into '<Match[1] in uppercase>\r'

If you want to place raw digit after ‘\$n’ you must delimit n with curly braces {}.

'a$12bc' -> 'a<Match[12]>bc'
'a${1}2bc' -> 'a<Match[1]>2bc'.

To use found named groups, use syntax ${name}, where "name" is valid identifier of previously found named group (starting with non-digit).


Splits AInputStr into APieces by regex occurrences.

Internally calls Exec / ExecNext

See also global function SplitRegExpr that you can use without explicit TRegExpr object creation.

Replace, ReplaceEx

function Replace (Const AInputStr : RegExprString;
  const AReplaceStr : RegExprString;
  AUseSubstitution : boolean= False)
 : RegExprString; overload;

function Replace (Const AInputStr : RegExprString;
  AReplaceFunc : TRegExprReplaceFunction)
 : RegExprString; overload;

function ReplaceEx (Const AInputStr : RegExprString;
  AReplaceFunc : TRegExprReplaceFunction):

Returns the string with regex occurencies replaced by the replace string.

If last argument (AUseSubstitution) is true, then AReplaceStr will be used as template for Substitution methods.

Expression := '((?i)block|var)\s*(\s*\([^ ]*\)\s*)\s*';
Replace ('BLOCK( test1)', 'def "$1" value "$2"', True);

Returns def "BLOCK" value "test1"

Replace ('BLOCK( test1)', 'def "$1" value "$2"', False)

Returns def "$1" value "$2"

Internally calls Exec / ExecNext

Overloaded version and ReplaceEx operate with callback function, so you can implement really complex functionality.

See also global function ReplaceRegExpr that you can use without explicit TRegExpr object creation.


Count of groups (subexpressions) found in last Exec / ExecNext call.

If there are no groups found, but some string was found (Exec* returned True), it returns 0. If no groups nor some string were found (Exec / ExecNext returned false), it returns -1.

Note, that some group may be not found, and for such group MathPos=MatchLen=-1 and Match=’’.

Expression := '(1)?2(3)?';
Exec ('123'): SubExprMatchCount=2, Match[0]='123', [1]='1', [2]='3'

Exec ('12'): SubExprMatchCount=1, Match[0]='12', [1]='1'

Exec ('23'): SubExprMatchCount=2, Match[0]='23', [1]='', [2]='3'

Exec ('2'): SubExprMatchCount=0, Match[0]='2'

Exec ('7') - return False: SubExprMatchCount=-1


Position (1-based) of group with specified index. Result is valid only after some match was found. First group has index 1, the entire match has index 0.

Returns -1 if no group with specified index was found.


Length of group with specified index. Result is valid only after some match was found. First group has index 1, the entire match has index 0.

Returns -1 if no group with specified index was found.


String of group with specified index. First group has index 1, the entire match has index 0. Returns empty string, if no such group was found.


Returns group index (1-based) from group name, which is needed for "named groups". Returns -1 if no such named group was found.


Returns Id of last error, or 0 if no errors occured (unusable if Error method raises exception). It also clears internal status to 0 (no errors).


Returns Error message for error with ID = AErrorID.


Returns position in regex, where P-code compilation was stopped.

Useful for error diagnostics.


Contains chars, treated as \s (initially filled with RegExprSpaceChars global constant).


Contains chars, treated as \w (initially filled with RegExprWordChars global constant).


Line separators (like \n in Unix), initially filled with RegExprLineSeparators global constant).

See also Line Boundaries


Boolean property, enables to detect paired line separator CR LF.

See also Line Boundaries

For example, if you need only Unix-style separator LF, assign LineSeparators := #$a and UseLinePairedBreak := False.

If you want to accept as line separators only CR LF but not CR or LF alone, then assign LineSeparators := '' (empty string) and UseLinePairedBreak := True.

By default, "mixed" mode is used (defined in RegExprLineSeparators global constant):

LineSeparators := #$d#$a; 
UseLinePairedBreak := True;

Behaviour of this mode is described in the Line Boundaries.


Compiles regular expression to internal P-code.

Useful for example for GUI regular expressions editors - to check regular expression without using it.


Shows P-code (compiled regular expression) as human-readable string.

Global constants


Escape character, by default backslash '\'.


Char used to prefix groups (numbered and named) in Substitute method, by default '$'.


Modifier i default value.


Modifier r default value.


Modifier s default value.


Modifier g default value.


Modifier m default value.


Modifier x default value.


Default for SpaceChars property.


Default value for WordChars property.   RegExprLineSeparators \~\~\~\~\~\~\~\~\~\~\~\~\~\~\~\~\~\~\~\~~

Default value for LineSeparators property.

Global functions

All this functionality is available as methods of TRegExpr, but with global functions you do not need to create TReExpr instance so your code would be more simple if you just need one function.


Returns True if the string matches the regular expression. Just like Exec in TRegExpr.


Splits the string by regular expression occurences. See also Split if you prefer to create TRegExpr instance explicitly.


function ReplaceRegExpr (
    const ARegExpr, AInputStr, AReplaceStr : RegExprString;
    AUseSubstitution : boolean= False
) : RegExprString; overload;

  TRegexReplaceOption = (rroModifierI,
  TRegexReplaceOptions = Set of TRegexReplaceOption;

function ReplaceRegExpr (
    const ARegExpr, AInputStr, AReplaceStr : RegExprString;
    Options :TRegexReplaceOptions
) : RegExprString; overload;

Returns the string with regular expressions replaced by the AReplaceStr. See also Replace if you prefer to create TRegExpr instance explicitly.

If last argument (AUseSubstitution) is True, then AReplaceStr will be used as template for Substitution methods:

ReplaceRegExpr (
  '((?i)block|var)\s*(\s*\([^ ]*\)\s*)\s*',
  'def "$1" value "$2"',

Returns def 'BLOCK' value 'test1'

But this one (note there is no last argument):

ReplaceRegExpr (
  '((?i)block|var)\s*(\s*\([^ ]*\)\s*)\s*',
  'def "$1" value "$2"'

Returns def "$1" value "$2"

Version with options

With Options you control \n behaviour (if rroUseOsLineEnd then \n is replaced with \n\r in Windows and \n in Linux). And so on.

  TRegexReplaceOption = (rroModifierI,


Replace all metachars with its safe representation, for example abc'cd.( is converted to abc\'cd\.\(

This function is useful for regex auto-generation from user input.


Makes list of subexpressions found in ARegExpr.

In ASubExps every item represents subexpression, from first to last, in format:

String - subexpression text (without ‘()’)

Low word of Object - starting position in ARegExpr, including ‘(’ if exists! (first position is 1)

High word of Object - length, including starting ‘(’ and ending ‘)’ if exist!

AExtendedSyntax - must be True if modifier /x os on, while using the regex.

Usefull for GUI editors of regex (you can find example of usage in REStudioMain.pas)

=========== ======= Result code Meaning =========== ======= 0           Success. No unbalanced brackets were found. -1          Not enough closing brackets ). -(n+1)      At position n it was found opening [ without corresponding closing ]. n           At position n it was found closing bracket ) without corresponding opening (. =========== ======= 

If Result <> 0, then ASubExprs can contain empty items or illegal ones.


ERegExpr = class (Exception)
   ErrorCode : integer; // error code. Compilation error codes are before 1000
   CompilerErrorPos : integer; // Position in r.e. where compilation error occured


In Unicode mode, all strings (InputString, Expression, internal strings) are of type UnicodeString/WideString, instead of simple "string". Unicode slows down performance, so use it only if you really need Unicode support.

To use Unicode, uncomment {$DEFINE UniCode} in regexpr.pas (remove off).