SelectionCriteria Property

Specify the criteria in statements of 3 elements: a noun, an operator, and a value. Consider the string "name != *.doc" . The noun is "name". The operator is "!=", implying "Not Equal". The value is "*.doc". That criterion, in English, says "all files with a name that does not end in the .doc extension."

Supported nouns include "name" (or "filename") for the filename; "atime", "mtime", and "ctime" for last access time, last modfied time, and created time of the file, respectively; "attributes" (or "attrs") for the file attributes; "size" (or "length") for the file length (uncompressed); and "type" for the type of object, either a file or a directory. The "attributes", "type", and "name" nouns all support = and != as operators. The "size", "atime", "mtime", and "ctime" nouns support = and !=, and >, >=, <, <= as well. The times are taken to be expressed in local time.

Specify values for the file attributes as a string with one or more of the characters H,R,S,A,I,L in any order, implying file attributes of Hidden, ReadOnly, System, Archive, NotContextIndexed, and ReparsePoint (symbolic link) respectively.

To specify a time, use YYYY-MM-DD-HH:mm:ss or YYYY/MM/DD-HH:mm:ss as the format. If you omit the HH:mm:ss portion, it is assumed to be 00:00:00 (midnight).

The value for a size criterion is expressed in integer quantities of bytes, kilobytes (use k or kb after the number), megabytes (m or mb), or gigabytes (g or gb).

The value for a name is a pattern to match against the filename, potentially including wildcards. The pattern follows CMD.exe glob rules: * implies one or more of any character, while ? implies one character. If the name pattern contains any slashes, it is matched to the entire filename, including the path; otherwise, it is matched against only the filename without the path. This means a pattern of "*\*.*" matches all files one directory level deep, while a pattern of "*.*" matches all files in all directories.

To specify a name pattern that includes spaces, use single quotes around the pattern. A pattern of "'* *.*'" will match all files that have spaces in the filename. The full criteria string for that would be "name = '* *.*'" .

The value for a type criterion is either F (implying a file) or D (implying a directory).

Some examples:

You can combine criteria with the conjunctions AND, OR, and XOR. Using a string like "name = *.txt AND size >= 100k" for the selectionCriteria retrieves entries whose names end in .txt, and whose uncompressed size is greater than or equal to 100 kilobytes.

For more complex combinations of criteria, you can use parenthesis to group clauses in the boolean logic. Absent parenthesis, the precedence of the criterion atoms is determined by order of appearance. Unlike the C# language, the AND conjunction does not take precendence over the logical OR. This is important only in strings that contain 3 or more criterion atoms. In other words, "name = *.txt and size > 1000 or attributes = H" implies "((name = *.txt AND size > 1000) OR attributes = H)" while "attributes = H OR name = *.txt and size > 1000" evaluates to "((attributes = H OR name = *.txt) AND size > 1000)". When in doubt, use parenthesis.

Using time properties requires some extra care. If you want to retrieve all entries that were last updated on 2009 February 14, specify "mtime >= 2009-02-14 AND mtime < 2009-02-15". Read this to say: all files updated after 12:00am on February 14th, until 12:00am on February 15th. You can use the same bracketing approach to specify any time period - a year, a month, a week, and so on.

The syntax allows one special case: if you provide a string with no spaces, it is treated as a pattern to match for the filename. Therefore a string like "*.xls" will be equivalent to specifying "name = *.xls". This "shorthand" notation does not work with compound criteria.

There is no logic in this class that insures that the inclusion criteria are internally consistent. For example, it's possible to specify criteria that says the file must have a size of less than 100 bytes, as well as a size that is greater than 1000 bytes. Obviously no file will ever satisfy such criteria, but this class does not check for or detect such inconsistencies.