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I have come across a regular expression that I don't fully understand - can somebody help me in deciphering it:
^home(?:\/|\/index\.asp)?(?:\?.+)?$ It is used in url matching and the above example matches the following urls:
home home/ home/?a home/?a=1 home/index.asp home/index.asp?a home/index.asp?a=1 It seems to me that the question marks within the brackets (?: don't do anything. Can somebody enlighten me.
The version of regex being used is the one supplied with Classic ASP and is being run on the server if that helps at all.
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(?:...) A non-capturing version of regular parentheses. Matches whatever regular expression is inside the parentheses, but the substring matched by the group cannot be retrieved after performing a match or referenced later in the pattern.
For example, the replacement pattern $1 indicates that the matched substring is to be replaced by the first captured group.
4. What does /[^(]* regular expression indicate? Explanation: The [^…] character class is used to match or draw any one character not between the brackets.
Simply put: \b allows you to perform a “whole words only” search using a regular expression in the form of \bword\b. A “word character” is a character that can be used to form words. All characters that are not “word characters” are “non-word characters”.
(?:) creates a non-capturing group. It groups things together without creating a backreference.
A backreference is a part you can refer to in the expression or a possible replacement (usually by saying \1 or $1 etc - depending on flavor). You can also usually extract them from a match afterwards when using regex in a programming language. The only reason for using (?:) is to avoid creating a new backreference, which avoids incrementing the group number, and saves (a usually negligible amount of) memory
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