/// \file

/// \ingroup Tutorials

/// A regular expression, often called a pattern, is an expression that describes a set of

/// strings. They are usually used to give a concise description of a set, without having to

/// list all elements.

/// The Unix utilities like sed and grep make extensive use of regular expressions. Scripting

/// languages like Perl have regular expression engines built directly into their syntax .

///

/// Extensive documentation about Regular expressions in Perl can be

/// found at: http://perldoc.perl.org/perlre.html

///

/// ROOT has this capability through the use of the P(erl) C(ompatible) R(egular) E(xpression)

/// - library, PCRE, see http://www.pcre.org

///

/// Its functionality can be accessed through the TPRegexp and TString class .

/// Note that in patterns taken from Perl all backslash character have to be replaced in the

/// C/C++ strings by two backslashes .

///

/// This macro shows several ways how to use the Match/Substitute capabilities of the

/// the TPRegexp class . It can be run as follows :

/// ~~~

/// .x regexp.C

/// ~~~

///

/// \macro_output

/// \macro_code

///

/// \author Eddy Offermann

#include "Riostream.h"

#include "TString.h"

#include "TPRegexp.h"

#include "TClonesArray.h"

#include "TObjString.h"

void regexp()

{

// Substitute example :

// Find a word that starts with "peper" and ends with "koek" .

TString s1("lekkere pepernotenkoek");

TPRegexp r1("\\bpeper(\\w+)koek\\b");

// Note that the TString class gives access to some of the simpler TPRegexp functionality .

// The following command returns the fully matched string .

cout << s1(r1) << endl;

// In the "Substitute" command, keep the middle part (indicated in the regexp by "(\\w+)"

// and the substitute string by "$1") and sandwich it between "wal" and "boom" .

r1.Substitute(s1,"wal$1boom");

cout << s1 << endl;

// Substitute example :

// Swap first two words in a string

TString s2("one two three");

TPRegexp("^([^ ]+) +([^ ]+)").Substitute(s2,"$2 $1");

cout << s2 << endl;

// Substitute example :

// $1, $2, and so on, in the substitute string are equivalent to whatever the corresponding set

// of parentheses match in the regexp string, counting opening parentheses from left to right .

// In the following example, we are trying to catch a date MMDDYYYY in a string and rearrange

// it to DDMMYYY . "(\\d{1,2}) matches only 1 or 2 digits etc .

TString s3("on 09/24/1959 the world stood still");

TPRegexp("\\b(\\d{1,2})/(\\d{1,2})/(\\d{4})\\b").Substitute(s3,"$2-$1-$3");

cout << s3 << endl;

// Match Example :

// The following example shows how to extract a protocol and port number from an URL string .

// Note again the parentheses in the regexp string : "(\\w+)" requires a non-empty

// alphanumeric string while "(\\d+)" wants a pure digital string .

// The matched substrings together with the full matched string are returned in a

// TObjArray . The first entry is the full string while next entries are the substrings

// in the order as listed in the regexp string .

//

// Note that there is also a Match(..) command that returns the positions of the

// substrings in the input string .

TString s4("http://fink.sourceforge.net:8080/index/readme.html");

TObjArray *subStrL = TPRegexp("^(\\w+)://[^/]+:(\\d+)/$").MatchS(s4);

const Int_t nrSubStr = subStrL->GetLast()+1;

if (nrSubStr > 2) {

const TString proto = ((TObjString *)subStrL->At(1))->GetString();

const TString port = ((TObjString *)subStrL->At(2))->GetString();

cout << "protocol: " << proto << " port: " << port << endl;

}

// Match Example :

// This example returns kTRUE if the email address is valid . For that it has to fulfil the following

// criteria:

// 1) It should be of the form string1@string2 . The "^" and "$" ensure that we compare the complete

// email string

// 2) ([\\w-\\.]+) :

// string1 is only allowed to be composed out of the alphanumeric characters, "-" and "." .

// The "+" ensures that string1 can not be empty .

// 3) string2 is matched against three different parts :

// a. ((\\[[0-9]{1,3}\\.[0-9]{1,3}\\.[0-9]{1,3}\\.)|(([\\w-]+\\.)+)) :

// This regular expression ensures that EITHER the string starts with "[" followed by three groups

// of numbers, separated by "." , where each group has 1 to 3 numbers, OR alphanumeric strings,

// possibly containing "-" characters, separated by "." .

// b. ([a-zA-Z]{2,4}|[0-9]{1,3}) :

// This part contains EITHER 2 to 4 alpha characters OR 1 to 3 numbers

// c. (\\]?) :

// At most one "]" character .

TString s5("fons.rademakers@cern.ch");

TPRegexp r5("^([\\w-\\.]+)@((\\[[0-9]{1,3}\\.[0-9]{1,3}\\.[0-9]{1,3}\\.)|(([\\w-]+\\.)+))([a-zA-Z]{2,4}|[0-9]{1,3})(\\]?)$");

cout << "Check if the email address \"" << s5 << "\" is valid: " << (r5.MatchB(s5) ? "TRUE" : "FALSE") << endl;

// Substitute Example with pattern modifier :

// Like in Perl, Substitute/Match commands accept modifier arguments . For instance a "g" modifier causes to

// match the regexp globally . In the example below, all words starting and ending with the character "n"

// are replaced by the word neutrino .

TString s6("neutron proton electron neutron");

TPRegexp("(n\\w+n)").Substitute(s6,"neutrino","g");

cout << s6 << endl;

}