GSAK (Geocaching Swiss Army Knife)
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Regular Expressions


Introduction 

GSAK uses the industry standard PCRE regular expression engine. PCRE is short for Perl Compatible Regular Expressions. It is the name of an open source library written in C by Phillip Hazel. The library is compatible with a great number of C compilers and operating systems. The following is just a summary of the supported syntax. For a full overview of the supported syntax please see this link

The macro related functions for using regular expression are:

RegEx           
RegExCount      
RegExData       
RegExEscape     
RegExPos     
RegExReplace    
RegExSub   

very good tutorial on regular expressions can be found here

Regular Expressions are a widely-used method of specifying patterns of text to search for. Special meta characters allow you to specify, for instance, that a particular string you are looking for occurs at the beginning or end of a line, or contains n recurrences of a certain character. 

Regular expressions look ugly for novices, but really they are very simple (well, usually simple ;) ) handy and powerful tool. 

Examples of a few geocaching related Regular expressions for the waypoint name would be:

^the => list all that start with "the"
\d$ =>  list all that have a number at the very end of the description
(boat|shed) => list all that have boat or shed somewhere (in any order)
(boat.*shed) => list all that have boat and shed but only in that order 
(boat.*shed)|(shed.*boat) => list all that have boat and shed somewhere (in any order)
\d{2,} => at least 2 numbers in a row anywhere in the description
cache.*\d => the word cache followed by a number (not directly after but anywhere) 
cache\d => the word cache followed directly by any single number

Note: The default behaviour for the GSAK regular expression engine is to ignore case. This means all matching is case insensitive. If you want to force the regular expression engine to respect case then begin your regular expression with the modifier (?-i). For example, to match the word AND (all uppercase) the regular expression would be: (?-i)AND 

Simple matches 

Any single character matches itself, unless it is a meta character with a special meaning described below. 

A series of characters matches that series of characters in the target string, so the pattern "bluh" would match "bluh'' in the target string. Quite simple, eh ? 

You can cause characters that normally function as meta characters or escape sequences to be interpreted literally by 'escaping' them by preceding them with a backslash "\", for instance: meta character "^" match beginning of string, but "\^" match character "^", "\\" match "\" and so on. 

Examples: 
  foobar          matches string 'foobar' 
  \^FooBarPtr     matches '^FooBarPtr' 

Escape sequences 

Characters may be specified using an escape sequence(s) syntax much like that used in C and Perl: "\n'' matches a newline, "\t'' a tab, etc. More generally, \xnn, where nn is a string of hexadecimal digits, matches the character whose ASCII value is nn. If you need wide (Unicode) character code, you can use '\x{nnnn}', where 'nnnn' - one or more hexadecimal digits. 

  \xnn     char with hex code nn 
  \x{nnnn} char with hex code nnnn (one byte for plain text and two bytes for unicode
  \t       tab (HT/TAB), same as \x09 
  \n       newline (NL), same as \x0a 
  \r       car.return (CR), same as \x0d 
  \f       form feed (FF), same as \x0c 
  \a       alarm (bell) (BEL), same as \x07 
  \e       escape (ESC), same as \x1b 

Examples: 
  foo\x20bar   matches 'foo bar' (note space in the middle) 
  \tfoobar     matches 'foobar' predefined by tab 


Character classes 

You can specify a character class, by enclosing a list of characters in [], which will match any one character from the list. 

If the first character after the "['' is "^'', the class matches any character not in the list. 

Examples: 
  foob[aeiou]r   finds strings 'foobar', 'foober' etc. but not 'foobbr', 'foobcr' etc. 
  foob[^aeiou]r  finds strings 'foobbr', 'foobcr' etc. but not 'foobar', 'foober' etc. 

Within a list, the "-'' character is used to specify a range, so that a-z represents all characters between "a'' and "z'', inclusive. 

If you want "-'' itself to be a member of a class, put it at the start or end of the list, or escape it with a backslash. If you want ']' you may place it at the start of list or escape it with a backslash. 

Examples: 
  [-az]      matches 'a', 'z' and '-' 
  [az-]      matches 'a', 'z' and '-' 
  [a\-z]     matches 'a', 'z' and '-' 
  [a-z]      matches all twenty six small characters from 'a' to 'z' 
  [\n-\x0D]  matches any of #10,#11,#12,#13. 
  [\d-t]     matches any digit, '-' or 't'. 
  []-a]      matches any char from ']'..'a'. 


Meta characters 

Meta characters are special characters which are the essence of Regular Expressions. There are different types of metacharacters, described below. 


Meta characters - line separators 

  ^      start of line 
  $      end of line 
  \A     start of text 
  \Z     end of text 
  .      any character in line 

Examples: 
  ^foobar     matches string 'foobar' only if it's at the beginning of line 
  foobar$     matches string 'foobar' only if it's at the end of line 
  ^foobar$    matches string 'foobar' only if it's the only string in line 
  foob.r      matches strings like 'foobar', 'foobbr', 'foob1r' and so on 

The "^" meta character by default is only guaranteed to match at the beginning of the input string/text, the "$" meta character only at the end. Embedded line separators will not be matched by "^'' or "$''. 
You may, however, wish to treat a string as a multi-line buffer, such that the "^'' will match after any line separator within the string, and "$'' will match before any line separator. You can do this by using the modifier (?m)
The \A and \Z are just like "^'' and "$'', except that they won't match multiple times when the modifier /m  is used, while "^'' and "$'' will match at every internal line separator. 

"^" is at the beginning of a input string, and, if modifier (?m) is On, also immediately following any occurrence of \x0D\x0A or \x0A or \x0D (if you are using Unicode version of TRegExpr, then also \x2028 or \x2029 or \x0B or \x0C or \x85). Note that there is no empty line within the sequence \x0D\x0A. 

"$" is at the end of a input string, and, if modifier (?m)  is On, also immediately preceding any occurrence of \x0D\x0A or \x0A or \x0D (if you are using Unicode version  of TRegExpr, then also \x2028 or \x2029 or \x0B or \x0C or \x85). Note that there is no empty line within the sequence \x0D\x0A. 

"." matches any character, but if you switch Off modifier (?s-) then "." doesn't match \x0D\x0A and \x0A and \x0D (if you are using Unicode version of TRegExpr, then also \x2028 and \x2029 and \x0B and \x0C and \x85). 

Note that "^.*$" (an empty line pattern) does not match the empty string within the sequence \x0D\x0A, but matches the empty string within the sequence \x0A\x0D. 

Multiline processing can be easily tuned for your own purpose with help of TRegExpr properties LineSeparators and LinePairedSeparator , you can use only Unix style separators \n or only DOS/Windows style \r\n or mix them together (as described above and used by default) or define your own line separators! 


Metacharacters - predefined classes 

  \w     an alphanumeric character (including "_") 
  \W     a nonalphanumeric 
  \d     a numeric character 
  \D     a non-numeric 
  \s     any space (same as [ \t\n\r\f]) 
  \S     a non space 

You may use \w, \d and \s within custom character classes

Examples: 
  foob\dr     matches strings like 'foob1r', ''foob6r' and so on but not 'foobar', 'foobbr' and so on 
  foob[\w\s]r matches strings like 'foobar', 'foob r', 'foobbr' and so on but not 'foob1r', 'foob=r' and so on 

TRegExpr uses properties SpaceChars and WordChars to define character classes \w, \W, \s, \S, so you can easily redefine it. 


Metacharacters - word boundaries 

  \b     Match a word boundary 
  \B     Match a non-(word boundary) 

A word boundary (\b) is a spot between two characters that has a \w on one side of it and a \W on the other side of it (in either order), counting the imaginary characters off the beginning and end of the string as matching a \W. 


Meta characters - iterators 

Any item of a regular expression may be followed by another type of meta characters - iterators. Using this meta characters you can specify number of occurrences of previous character, meta character or subexpression

  *      zero or more ("greedy"), similar to {0,} 
  +      one or more ("greedy"), similar to {1,} 
  ?      zero or one ("greedy"), similar to {0,1} 
  {n}    exactly n times ("greedy") 
  {n,}   at least n times ("greedy") 
  {n,m}  at least n but not more than m times ("greedy") 
  *?     zero or more ("non-greedy"), similar to {0,}? 
  +?     one or more ("non-greedy"), similar to {1,}? 
  ??     zero or one ("non-greedy"), similar to {0,1}? 
  {n}?   exactly n times ("non-greedy") 
  {n,}?  at least n times ("non-greedy") 
  {n,m}? at least n but not more than m times ("non-greedy") 

So, digits in curly brackets of the form {n,m}, specify the minimum number of times to match the item n and the maximum m. The form {n} is equivalent to {n,n} and matches exactly n times. The form {n,} matches n or more times. There is no limit to the size of n or m, but large numbers will chew up more memory and slow down r.e. execution. 

If a curly bracket occurs in any other context, it is treated as a regular character. 

Examples: 
  foob.*r     matches strings like 'foobar', 'foobalkjdflkj9r' and 'foobr' 
  foob.+r     matches strings like 'foobar', 'foobalkjdflkj9r' but not 'foobr' 
  foob.?r     matches strings like 'foobar', 'foobbr' and 'foobr' but not 'foobalkj9r' 
  fooba{2}r   matches the string 'foobaar' 
  fooba{2,}r  matches strings like 'foobaar', 'foobaaar', 'foobaaaar' etc. 
  fooba{2,3}r matches strings like 'foobaar', or 'foobaaar' but not 'foobaaaar' 

A little explanation about "greediness". "Greedy" takes as many as possible, "non-greedy" takes as few as possible. For example, 'b+' and 'b*' applied to string 'abbbbc' return 'bbbb', 'b+?' returns 'b', 'b*?' returns empty string, 'b{2,3}?' returns 'bb', 'b{2,3}' returns 'bbb'. 

Meta characters - alternatives 

You can specify a series of alternatives for a pattern using "|'' to separate them, so that fee|fie|foe will match any of "fee'', "fie'', or "foe'' in the target string (as would f(e|i|o)e). The first alternative includes everything from the last pattern delimiter ("('', "['', or the beginning of the pattern) up to the first "|'', and the last alternative contains everything from the last "|'' to the next pattern delimiter. For this reason, it's common practise to include alternatives in parentheses, to minimize confusion about where they start and end. 
Alternatives are tried from left to right, so the first alternative found for which the entire expression matches, is the one that is chosen. This means that alternatives are not necessarily greedy. For example: when matching foo|foot against "barefoot'', only the "foo'' part will match, as that is the first alternative tried, and it successfully matches the target string. (This might not seem important, but it is important when you are capturing matched text using parentheses.) 
Also remember that "|'' is interpreted as a literal within square brackets, so if you write [fee|fie|foe] you're really only matching [feio|]. 

Examples: 
  foo(bar|foo)  matches strings 'foobar' or 'foofoo'. 


Modifiers 

Any of these modifiers may be embedded within the regular expression itself using the (?...) construct. 

i 
Do case-insensitive pattern matching (using installed in you system locale settings) see also invertcase.


Treat string as multiple lines. That is, change "^'' and "$'' from matching at only the very start or end of the string to the start or end of any line anywhere within the string, see also Line separators


Treat string as single line. That is, change ".'' to match any character whatsoever, even a line separators (see also Line separators )


Perl extensions 

(?ims-ims) 
You may use it into r.e. for modifying modifiers by the fly. If this construction inlined into subexpression, then it affects only this subexpression 

Examples: 
  (?i)Saint-Petersburg       matches 'Saint-petersburg' and 'Saint-Petersburg' 
  (?i)Saint-(?-i)Petersburg  matches 'Saint-Petersburg' but not 'Saint-petersburg' 
  (?i)(Saint-)?Petersburg    matches 'Saint-petersburg' and 'saint-petersburg' 
  ((?i)Saint-)?Petersburg    matches 'saint-Petersburg', but not 'saint-petersburg' 


(?#text) 
A comment, the text is ignored. Note that comments are closed soon as it sees a ")", so there is no way to put a literal ")" in the comment.
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