Multicharacter Regular Expressions

You can use the following rules to build multicharacter regular expressions:

Parentheses group parts of regular expressions together into grouped subexpressions that you can be treat as a single unit; for example, (ha)+ matches one or more instances of "ha".
A plus sign (+) following a one-character regular expression or grouped subexpressions matches one or more occurrences of the regular expression; for example, [a-z]+ matches one or more lowercase characters.
An asterisk (*) following a one-character regular expression or grouped subexpressions matches zero or more occurrences of the regular expression; for example, [a-z]* matches zero or more lowercase characters. Since a regular expression followed by an * can match the empty string, you can get unexpected results when there is no actual match. For example,
```
<cfoutput>REReplace("Hello","[T]*","7","ALL") -

#REReplace("Hello","[T]*","7","ALL")#<BR></cfoutput>
```
results in the following output:
REReplace("Hello","[T]*","7","ALL") - 7H7e7l7l7o
Here the regular expression [T]* can match empty strings. It first matches the empty string before "H" in "Hello". Next, (note that the "ALL" artgument tells REReplace to replace all instances of an expression), the empty string before "e" is matched and so on until the empty string before "o" is matched. This result might be unexpected. The workarounds for these types of problems are specific to each case. In some cases you can use [T]+, which requires at least one "T", instead of [T]*. Alternatively, you might be able to specify an additional pattern after [T]*. In the following example the regular expression has a "W" at the end:
<cfoutput>REReplace("Hello World","[T]*W","7","ALL") - #REReplace("Hello World","[T]*W","7","ALL")#<BR></cfoutput>
This expression results in the following more predictable output:
REReplace("Hello World","[T]*W","7","ALL") - Hello 7orld
A one-character regular expression or grouped subexpression followed by a question mark (?) matches zero or one occurrences of the regular expression; for example, xy?z matches either "xyz" or "xz".
The concatenation of regular expressions creates a regular expression that matches the corresponding concatenation of strings; for example, [A-Z][a-z]* matches any capitalized word.
The OR character (|) allows a choice between two regular expressions; for example, jell(y|ies) matches either "jelly" or "jellies".
The following suffixes match repetitions of a regular expresion:
- {m,n}, where m is 0 or greater and n is greater than or equal to m, forces a match of m through n (inclusive) occurrences of the preceding regular expression; for example, (ba){2,4} matches "baba", "bababa", and "babababa", but not "ba" or "babababababa".
- {m,} forces a match of at least m occurrences of the preceding regular expression. The syntax {,n} is not allowed.

An excellent reference on regular expressions is Mastering Regular Expressions, Jeffrey E. F. Friedl. O'Reilly & Associates, Inc., 1997. ISBN: 1-56592-257-3, http://www.oreilly.com.

Limiting input string size

In CFML regular expression functions, large input strings (greater than approximately 20,000 characters) cause a debug assertion failure and a regular expression error occurs. To avoid this, break your input into smaller chunks, as the following example shows. Here the variable input has a size greater than 50000.

<cfset test = mid(input, 1, 20000)>

<cfset out1 = REReplace(test, "[ #Chr(9)##Chr(13)##Chr(10)#]+#Chr(13)##Chr(10)#", "#chr(10)#", "ALL")>

<cfset test = mid(input, 20001, 20000)>

<cfset out2 = REReplace(test, "[ #Chr(9)##Chr(13)##Chr(10)#]+#Chr(13)##Chr(10)#", "#chr(10)#", "ALL")>

<cfset test = mid(input, 40001, len(input) - 40000)>

<cfset out3 = REReplace(test, "[ #Chr(9)##Chr(13)##Chr(10)#]+#Chr(13)##Chr(10)#", "#chr(10)#", "ALL")>

<cfset result = out1 & out2 & out3>

Anchoring a regular expression to a string

You can anchor all or part of a regular expression to either the beginning or end of the string being searched:

If the caret (^) is at the beginning of a (sub)expression, the matched string must be at the beginning of the string being searched.
If the dollar sign ($) is at the end of a (sub)expression, the matched string must be at the end of the string being searched.

Developing ColdFusion Applications
Using Regular Expressions in Functions