Adobe 38043740 Developing Applications - Page 146

DEVELOPING COLDFUSION 9 APPLICATIONS 141 The CFML Programming Language Escaping special characters in replacement strings You use the backslash character, \, to escape backreference and case-conversion characters in replacement strings. For example, to include a literal "\u" in a replacement string, escape it, as in "\\u". Omitting subexpressions from backreferences By default, a set of parentheses will both group the subexpression and capture its matched text for later referral by backreferences. However, if you insert "?:" as the first characters of the subexpression, ColdFusion performs all operations on the subexpression except that it will not capture the corresponding text for use with a back reference. This is useful when alternating over subexpressions containing differing numbers of groups would complicate backreference numbering. For example, consider an expression to insert a "Mr." in between Bonjour|Hi|Hello and Bond, using a nested group for alternating between Hi & Hello: #REReplace(string, regex, replaceString)# This example returns "Hello Mr. Bond". If you did not prohibit the capturing of the Hi/Hello group, the \2 backreference would end up referring to that group instead of " Bond", and the result would be "Hello Mr.ello". Returning matched subexpressions The REFind and REFindNoCase functions return the location in the search string of the first match of the regular expression. Even though the search string in the next example contains two matches of the regular expression, the function only returns the index of the first: To find all instances of the regular expression, you must call the REFind and REFindNoCase functions multiple times. Both the REFind and REFindNoCase functions take an optional third parameter that specifies the starting index in the search string for the search. By default, the starting location is index 1, the beginning of the string. To find the second instance of the regular expression in this example, you call REFind with a starting index of 8: In this case, the function returns an index of 9, the starting index of the second string " BIG ". To find the second occurrence of the string, you must know that the first string occurred at index 5 and that the string's length was 5. However, REFind only returns starting index of the string, not its length. So, you either must know the length of the matched string to call REFind the second time, or you must use subexpressions in the regular expression. The REFind and REFindNoCase functions let you get information about matched subexpressions. If you set these functions' fourth parameter, ReturnSubExpression, to True, the functions return a CFML structure with two arrays, pos and len, containing the positions and lengths of text strings that match the subexpressions of a regular expression, as the following example shows: Last updated 1/20/2012