List of characters that need escape, i.e., \

Anyone know what other characters besides the dot (.) need to be preceded
by the escape (\) character?
Thanks.
tlwtheq - Tue Mar 19 07:41:54 EDT 2013

Re: List of characters that need escape, i.e., \
SystemAdmin - Tue Mar 19 10:37:49 EDT 2013

Re: List of characters that need escape, i.e., \
tlwtheq - Tue Mar 19 10:44:34 EDT 2013

Re: List of characters that need escape, i.e., \
tlwtheq - Tue Mar 19 11:22:02 EDT 2013

Re: List of characters that need escape, i.e., \
llandale - Tue Mar 19 14:16:56 EDT 2013

Re: List of characters that need escape, i.e., \
tlwtheq - Tue Mar 19 14:21:43 EDT 2013

Re: List of characters that need escape, i.e., \
Mathias Mamsch - Tue Mar 19 17:44:09 EDT 2013

Well ^ is kind of an exception, you do not need to escape it, unless it is at the beginning of the regexp expression, there it has a special meaning. However to be safe I would always escape it. With the below code you can easily test escaping rules yourself.
 

string s = "^x"
 
Regexp re1 = regexp2 "^x" // does not match
Regexp re2 = regexp2 "^^x" // does match 
Regexp re3 = regexp2 "\^x" // does match 
 
print (re1 s)
print (re2 s)
print (re3 s)

Regards, Mathias

Mathias Mamsch, IT-QBase GmbH, Consultant for Requirement Engineering and D00RS

Re: List of characters that need escape, i.e., \
Mathias Mamsch - Tue Mar 19 17:48:49 EDT 2013

string s = "^x"
 
Regexp re1 = regexp2 "^x" // does not match
Regexp re2 = regexp2 "^^x" // does match 
Regexp re3 = regexp2 "\^x" // does match 
 
print (re1 s)
print (re2 s)
print (re3 s)

And ? of course needs to be escaped too ;-) Well its funny, the following code
 

for (i = 32; i < 127; i++) {
 
   char c = charOf i
   string s = "x" c ""
 
   noError()
   Regexp re1 = regexp2 "^x" c "$" // does not match
   string sErr = lastError()
 
   if (!null sErr || !(re1 s)) print c " "
}

results in: ( ) * + ? [ \

Regards, Mathias

Mathias Mamsch, IT-QBase GmbH, Consultant for Requirement Engineering and D00RS

Re: List of characters that need escape, i.e., \
llandale - Wed Mar 20 11:24:13 EDT 2013

for (i = 32; i < 127; i++) {
 
   char c = charOf i
   string s = "x" c ""
 
   noError()
   Regexp re1 = regexp2 "^x" c "$" // does not match
   string sErr = lastError()
 
   if (!null sErr || !(re1 s)) print c " "
}

Re: List of characters that need escape, i.e., \
Mathias Mamsch - Wed Mar 20 17:17:13 EDT 2013

Re: List of characters that need escape, i.e., \
tlwtheq - Wed Mar 20 23:34:49 EDT 2013

Re: List of characters that need escape, i.e., \
Fu Lin Yiu - Tue Nov 26 15:50:21 EST 2013

//------------------------------------------------------------------------------
// Use this for RegExp escaping of any character except backslash ( \ )
//     NOTE: Use of this function is not needed unless you wish to use
//           a regular expression "special char"
//------------------------------------------------------------------------------
string reEsc(char ch) {
    return "\\" ch "";
}
//------------------------------------------------------------------------------
// Use this to RegExp escape strings.
//     NOTE A - It is standard DXL practice to represent
//              a backslash ( \ ) as "\\".  This policy applies here as well.
//     NOTE B - Use the separate function
//                  string reEsc(char);
//              to escape non-backslash single characters
//     NOTE C - DXL "gotcha" warning.  When appending a bunch of functions
//              that have string arguments and return string together, surround
//              function calls with () to thwart argument bleed-through.
//------------------------------------------------------------------------------
string reEsc(string str) {
    string retVal = "";
    int i;
    for (i = 0; i < length(str); i++) {
        if (str[i] == '\\') {
            retVal = retVal "\\\\";
        } else {
            retVal = retVal str[i] "";
        }
    }
    return retVal;
}
//------------------------------------------------------------------------------
// EXAMPLE: using http://www.myregextester.com/index.php
//------------------------------------------------------------------------------
// NOTE: This example parses rich text which is ugly to start with!
//
// LET SOURCE TEXT (as pasted into My RegEx Tester page):
//     {\pntext\'B7\tab}{\*\pn\pnlvlblt\pnindent0{\pntxtb\'B7}}\li1440 Hi
//
// LET MATCH PATTERN (as pasted into My RegEx Tester page):
//     {\\\*\\pn\\pnlvlblt.*}
//
// My RegEx Tester page results:
//     {\*\pn\pnlvlblt\pnindent0{\pntxtb\'B7}}
//
// OBJECTIVES: Upon getting a RegEx expression working correctly (not trivial),
//             transpose it into DXL with a minimum chance of screwing it up
//             in the process (one extra/missing backslash and it is late for
//             supper).
//
// TRANSPOSING NOTES: Here are the markers and what to do with them.
//       {\\\*\\pn\\pnlvlblt.*}
//       ^ ^^^^               ^
// STEP: AAABBCCCCCCCCCCCCCCCCC
//                  AAA: (reEsc("{\\"))
//                   BB: (reEsc('*'))
//    CCCCCCCCCCCCCCCCC: (reEsc("\\pn\\pnlvlblt.*}"))
//------------------------------------------------------------------------------
void regExpTest() {
    string sourceToParse = //-
"{\\pntext\\'B7\\tab}{\\*\\pn\\pnlvlblt\\pnindent0{\\pntxtb\\'B7}}\\li1440 Hi";
    // find: {\\*\\pn\\pnlvlblt ... } in rich text
    Regexp re;
    re = regexp2( (reEsc("{\\")) (reEsc('*')) (reEsc("\\pn\\pnlvlblt.*}")));
    if (re sourceToParse) {
        print("Found pnlvlblt '"     //-
              sourceToParse[match 0] //-
              "':\n"                 //-
              sourceToParse          //-
              "\n"                    );
        print("Matched substring starts at " (start(0)) //-
              " and ends at " (end(0)) "\n"             );
    } else {
        print("No pnlvlblt in " sourceToParse "\n");
    }
}
// Launch example:
regExpTest();
//------------------------------------------------------------------------------
// Example's output:
//------------------------------------------------------------------------------
// Found pnlvlblt '{\*\pn\pnlvlblt\pnindent0{\pntxtb\'B7}}':
// {\pntext\'B7\tab}{\*\pn\pnlvlblt\pnindent0{\pntxtb\'B7}}\li1440 Hi
// Matched substring starts at 17 and ends at 55
//------------------------------------------------------------------------------
//------------------------------------------------------------------------------
// DXL Manual Says ...
//     The following symbols can be used in Regexp expressions:
//------------------------------------------------------------------------------
//   Chars: *
// Meaning: zero or more occurrences
// Example: a*
// Matches: any number of a characters, or none
//------------------------------------------------------------------------------
//   Chars: +
// Meaning: one or more occurrences
// Example: x+
// Matches: one or more x characters
//------------------------------------------------------------------------------
//   Chars: .
// Meaning: any single character except new line
// Example: .*
// Matches: any number of any characters (any string)
//------------------------------------------------------------------------------
//   Chars: \
// Meaning: escape (literal text char)
// Example: \.
// Matches: literally a . (dot) character
//------------------------------------------------------------------------------
//   Chars: ^
// Meaning: start of the string (if at start of Regexp)
// Example: ^The.*
// Matches: any string starting with The or starting with The after any
//          new line(see also [ ] below)
//------------------------------------------------------------------------------
//   Chars: $
// Meaning: end of the string (if at end of Regexp)
// Example: end\\.$
// Matches: any string ending with end.
//------------------------------------------------------------------------------
//   Chars: ( )
// Meaning: Groupings
// Example: (ref) + (bind) *
// Matches: at least one ref string then any number of bind strings
//------------------------------------------------------------------------------
//   Chars: [ ]
// Meaning: character range (letters or digits)
// Example: [sS]hall.*\\.$
// Matches: any string containing shall or Shall and ending in a literal
//          dot (any requirement sentence)
//
// Example: [^abc]
// Matches: any character except a, b, or c
//
// Example: [a-zA-Z]
// Matches: any alphabetic character
//
// Example: [0-9]
// Matches: any digit
//------------------------------------------------------------------------------
//   Chars: |
// Meaning: Alternative
// Example: (dat|doc)
// Matches: either the string dat or the string doc
//------------------------------------------------------------------------------
//------------------------------------------------------------------------------
// Mathias Mamsch says:
//     "Well its funny , the following code results in: ( ) * + ? [ \ "
//
// I find that "?" seems to work in regular expressions but the DXL manual
// does not mention it.
//
// What else works? ... Left as an exercise for the reader ... Welcome to DOORS!
//------------------------------------------------------------------------------
//------------------------------------------------------------------------------
// REFERENCES:
//     http://www.addedbytes.com/cheat-sheets/regular-expressions-cheat-sheet/
//------------------------------------------------------------------------------
 

Regards ...