\hypertarget{qore_regex_qore_regex_intro}{}\doxysection{Qore Regular Expression Introduction}\label{qore_regex_qore_regex_intro}
Regular expression functionality in Qore is provided by \href{http://www.pcre.org}{\texttt{ PCRE\+: Perl-\/\+Compatible Regular Expression library}}.

Using this library, Qore implements regular expression pattern matching using very simple syntax with semantics similar to those of \href{http://www.perl.org}{\texttt{ Perl 5}}. One difference between Qore and Perl to keep in mind is that \mbox{\hyperlink{qore_regex_qore_regex_backreferences}{backreferences}} in Qore are referenced as {\ttfamily \$1}, {\ttfamily \$2}, {\ttfamily \$3}, etc which differs from Perl\textquotesingle{}s syntax (which uses numbered backslashes instead).

\begin{DoxyParagraph}{Examples\+:}

\begin{DoxyCode}{0}
\DoxyCodeLine{\textcolor{comment}{\# call process() if the string starts with an alphanumeric character}}
\DoxyCodeLine{\textcolor{keywordflow}{if} (str =\string~ /\string^[[:alnum:]]/)}
\DoxyCodeLine{    process(str);}

\end{DoxyCode}
 
\begin{DoxyCode}{0}
\DoxyCodeLine{\textcolor{comment}{\# example of using regular expressions in a switch statement}}
\DoxyCodeLine{switch (str) \{}
\DoxyCodeLine{    case /\string^[\string^[:alnum:]]/: \textcolor{keywordflow}{return} \textcolor{keyword}{True};}
\DoxyCodeLine{    case /\string^[0-\/9]/: \textcolor{keywordflow}{return} \textcolor{keyword}{False};}
\DoxyCodeLine{    default: throw \textcolor{stringliteral}{"{}ERROR"{}}, sprintf(\textcolor{stringliteral}{"{}invalid string \%y"{}}, str);}
\DoxyCodeLine{\}}

\end{DoxyCode}
 
\begin{DoxyCode}{0}
\DoxyCodeLine{\textcolor{comment}{\# regular expression substitution + ignore case \& global options}}
\DoxyCodeLine{str =\string~ s/abc/xyz/gi;}

\end{DoxyCode}
 
\begin{DoxyCode}{0}
\DoxyCodeLine{\textcolor{comment}{\# prefix all non-\/alphanumeric characters with a backslash}}
\DoxyCodeLine{str =\string~ s/([\string^[:alnum:]])/\(\backslash\)\(\backslash\)\$1/g;}

\end{DoxyCode}
 
\begin{DoxyCode}{0}
\DoxyCodeLine{\textcolor{comment}{\# regular expression substring extraction}}
\DoxyCodeLine{*list l = (str =\string~ x/(?:(\(\backslash\)w+):(\(\backslash\)w+):)(\(\backslash\)w+)/);}

\end{DoxyCode}

\end{DoxyParagraph}
\hypertarget{qore_regex_qore_regex_operators}{}\doxysection{Qore Regular Expression Operators}\label{qore_regex_qore_regex_operators}
The following is a list of operators based on regular expressions (or similar to regular expressions in the case of the transliteration operator).

{\bfseries{Regular Expression Operators}}  \tabulinesep=1mm
\begin{longtabu}spread 0pt [c]{*{2}{|X[-1]}|}
\hline
{\bfseries{Operator}} &{\bfseries{Description}}  \\\cline{1-2}
\mbox{\hyperlink{operators_regex_match_operator}{Regular Expression Match Operator (=$\sim$)}} &Returns \mbox{\hyperlink{basic_data_types_True}{True}} if the regular expression matches a string  \\\cline{1-2}
\mbox{\hyperlink{operators_regex_no_match_operator}{Regular Expression No Match Operator (!$\sim$)}} &Returns \mbox{\hyperlink{basic_data_types_True}{True}} if the regular expression does not match a string  \\\cline{1-2}
\mbox{\hyperlink{operators_regex_subst_operator}{Regular Expression Substitution Operator}} &Substitutes text in a string based on matching a regular expression  \\\cline{1-2}
\mbox{\hyperlink{operators_regex_extract_operator}{Regular Expression Pattern Extraction Operator}} &Returns a list of substrings in a string based on matching patterns defined by a regular expression  \\\cline{1-2}
\mbox{\hyperlink{operators_transliteration_operator}{Transliteration Operator}} &Not a regular expression operator; transliterates one or more characters to other characters in a string  \\\cline{1-2}
\end{longtabu}


See the table below for valid regular expression options.\hypertarget{qore_regex_qore_regex_options}{}\doxysubsection{Qore Regular Expression Operator Options}\label{qore_regex_qore_regex_options}
{\bfseries{Regular Expression Options}}  \tabulinesep=1mm
\begin{longtabu}spread 0pt [c]{*{2}{|X[-1]}|}
\hline
{\bfseries{Option}} &{\bfseries{Description}}  \\\cline{1-2}
{\ttfamily i}  &Ignores case when matching  \\\cline{1-2}
{\ttfamily m}  &makes start-\/of-\/line ({\ttfamily $^\wedge$}) or end-\/of-\/line ({\ttfamily \$}) match after or before any newline in the subject string  \\\cline{1-2}
{\ttfamily s}  &makes a dot ({\ttfamily .}) match a newline character  \\\cline{1-2}
{\ttfamily x}  &ignores whitespace characters and enables comments prefixed by {\ttfamily \#}  \\\cline{1-2}
{\ttfamily u}  &extends Posix character matching to Unicode characters  \\\cline{1-2}
{\ttfamily g}  &makes global substitutions or global extractions (only applicable with the substitution and extraction operators)  \\\cline{1-2}
\end{longtabu}
\hypertarget{qore_regex_qore_regex_functions}{}\doxysection{Qore Regular Expression Functions}\label{qore_regex_qore_regex_functions}
The following is a list of functions providing regular expression functionality where the pattern may be given at run-\/time\+:

{\bfseries{Regular Expression Functions}}  \tabulinesep=1mm
\begin{longtabu}spread 0pt [c]{*{2}{|X[-1]}|}
\hline
{\bfseries{Function}} &{\bfseries{Description}}  \\\cline{1-2}
regex() &Returns \mbox{\hyperlink{basic_data_types_True}{True}} if the regular expression matches a string  \\\cline{1-2}
regex\+\_\+subst() &Substitutes a pattern in a string based on regular expressions and returns the new string  \\\cline{1-2}
regex\+\_\+extract() &Returns a list of substrings in a string based on matching patterns defined by a regular expression  \\\cline{1-2}
\end{longtabu}
\hypertarget{qore_regex_qore_regex_escape_patterns}{}\doxysection{Qore Regular Expression Escape Codes}\label{qore_regex_qore_regex_escape_patterns}
Escape characters in the pattern string are processed by the \href{http://www.pcre.org}{\texttt{ PCRE}} library similar to how Perl5 handles escape characters.\hypertarget{qore_regex_qore_regex_escape_replacement_string}{}\doxysubsection{Qore Regular Expression Replacement String Escape Codes}\label{qore_regex_qore_regex_escape_replacement_string}
Regular expression substitution expressions have the following pattern\+:
\begin{DoxyItemize}
\item {\ttfamily s/}{\itshape \texorpdfstring{$<$}{<}pattern\texorpdfstring{$>$}{>}}{\ttfamily /}{\itshape \texorpdfstring{$<$}{<}replacement\texorpdfstring{$>$}{>}}{\ttfamily /}
\end{DoxyItemize}

The escape codes in the following table are supported in the replacement string.

{\bfseries{Regular Expression Replacement String Escape Codes}}  \tabulinesep=1mm
\begin{longtabu}spread 0pt [c]{*{6}{|X[-1]}|}
\hline
{\bfseries{Escape}} &{\bfseries{ASCII}} &{\bfseries{Decimal}} &{\bfseries{Octal}} &{\bfseries{Hex}} &{\bfseries{Description}}  \\\cline{1-6}
\textbackslash{}a &{\ttfamily BEL}  &{\ttfamily 7}  &{\ttfamily 007}  &{\ttfamily 07}  &alarm or bell  \\\cline{1-6}
\textbackslash{}b &{\ttfamily BS}  &{\ttfamily 8}  &{\ttfamily 010}  &{\ttfamily 08}  &backspace  \\\cline{1-6}
\textbackslash{}e &{\ttfamily ESC}  &{\ttfamily 27}  &{\ttfamily 033}  &{\ttfamily 1B}  &escape character  \\\cline{1-6}
\textbackslash{}f &{\ttfamily FF}  &{\ttfamily 12}  &{\ttfamily 014}  &{\ttfamily 0C}  &form feed  \\\cline{1-6}
\textbackslash{}n &{\ttfamily LF}  &{\ttfamily 10}  &{\ttfamily 012}  &{\ttfamily 0A}  &line feed  \\\cline{1-6}
\textbackslash{}r &{\ttfamily CR}  &{\ttfamily 13}  &{\ttfamily 015}  &{\ttfamily 0D}  &carriage return  \\\cline{1-6}
\textbackslash{}t &{\ttfamily HT}  &{\ttfamily 9}  &{\ttfamily 011}  &{\ttfamily 09}  &horizontal tab  \\\cline{1-6}
\textbackslash{}v &{\ttfamily VT}  &{\ttfamily 11}  &{\ttfamily 013}  &{\ttfamily 0B}  &vertical tab  \\\cline{1-6}
\textbackslash{}\$ &{\ttfamily \$}  &{\ttfamily 36}  &{\ttfamily 044}  &{\ttfamily 24}  &a literal dollar sign character  \\\cline{1-6}
\textbackslash{}\textbackslash{} &{\ttfamily \textbackslash{}}  &{\ttfamily 134}  &{\ttfamily 092}  &{\ttfamily 5C}  &a literal backslash character  \\\cline{1-6}
\textbackslash{}\mbox{[}0-\/7\mbox{]}\mbox{[}0-\/7\mbox{]}\mbox{[}0-\/7\mbox{]} &-\/ &-\/ &-\/ &-\/ &the ASCII character represented by the octal code  \\\cline{1-6}
\end{longtabu}


Otherwise any backslashes in the replacement string will be copied literally to the output string.\hypertarget{qore_regex_qore_regex_backreferences}{}\doxysection{Qore Regular Expression Backreferences}\label{qore_regex_qore_regex_backreferences}
\mbox{\hyperlink{namespace_qore}{Qore}} uses {\ttfamily \$}{\itshape num} for backreferences in regular expression substitution expressions. The first backreference is {\ttfamily \$1}, the second \$2, and so on.

\begin{DoxyParagraph}{Example}

\begin{DoxyCode}{0}
\DoxyCodeLine{\textcolor{comment}{\# prefix all non-\/alphanumeric characters with a backslash}}
\DoxyCodeLine{str =\string~ s/([\string^[:alnum:]])/\(\backslash\)\(\backslash\)\$1/g;}

\end{DoxyCode}
 
\begin{DoxyCode}{0}
\DoxyCodeLine{\textcolor{comment}{\# remove parentheses from string at the beginning of the line}}
\DoxyCodeLine{str =\string~ s/\string^\(\backslash\)((.*)\(\backslash\))/\$1/;}

\end{DoxyCode}
 
\end{DoxyParagraph}