Regular expressions.
You might have seen several of Quick Search or Quick Select fields in ZModeler dialog boxes (Textures Browser, Select\[By Name], Display\[By Name], File\Merge). When you type there particular name (of an object, texture, etc.) full names that match are get selected. These matching is performed via Regular expression compare.
Regular expression matching allows you to test whether a string fits a specific syntactic shape. You can also search a text string for a sub-string that fits a pattern. So, regular expression describes a set of strings, that matches certain pattern. This can be very usful when you deal with lots of objects in scene and want to show/hide/select some of them (in case you gave them names with some regard, not just "obj01", "obj02",..., "obj716"). So, when you type something in such a search-boxes, you type a regular expression, so some basic syntax might be very helpfull.
A regular expression is a set of rules that describes a generalised string. If the characters that make up a particular string conform to the rules of a particular regular expression, the regular expression is said to match that string.
A few concrete examples usually help after an overblown definition like that one. The regular expression b. matches the strings bovine, above, Bobby, and Bob Jones, but not the strings Bell, b, or Bob. That's because the expression insists that the letter b (lowercase) must be in the string and must be followed immediately by another character.
The regular expression b+, on the other hand, requires the lowercase letter b at least once. This expression matches b and Bob in addition to the example matches for b. in the preceding paragraph. The regular expression b* requires zero or more bs, so it matches any string. That seems to be fairly useless, but it makes more sense as part of a larger regular expression. Bob*y, for example, matches all of Boy, Boby, and Bobby but not Boboby.
Assertions
Several so-called assertions are used to anchor parts of the pattern to word or string boundaries. The ^ assertion matches the start of a string, so the regular expression ^fool matches fool and foolhardy but not tomfoolery or April fool. The following table lists the assertions.
Regular-Expression Assertions
| Assertion | Matches | Example | Matches | Doesn't Match |
|---|---|---|---|---|
| ^ | Start of string | ^fool | foolish | Tomfoolery |
| $ | End of string | fool$ | April fool | Foolish |
| \b | Word boundary | be\bside | be side | Beside |
| \B | Nonword boundary | be\Bside | beside | be side |
Atoms
The . (period) that you saw in b. earlier in this chapter is an example of a regular-expression atom. Atoms are, as the name suggests, the fundamental building blocks of a regular expression. A full list of atoms appears in the following table.
Regular-Expression Atoms
| Atom | Matches | Example | Matches | Doesn't Match |
|---|---|---|---|---|
| Period (.) | Any character | b.b | Bob | bb |
| List of characters in brackets | Any one of those characters | ^[Bb] | Bob, bob | RBob |
| Regular expression in parentheses | Anything that regular expression matches | ^a(b.b)c$ | Abobc | abbc |
Quantifiers
A quantifier is a modifier for an atom. It can be used to specify that a particular atom must appear at least once, as in b+. The atom quantifiers are listed in the following table.
Regular-Expression Atom Quantifiers
| Quantifier | Matches | Example | Matches | Doesn't Match |
|---|---|---|---|---|
| * | Zero or more instances of the atom | ab*c | ac, abc | abb |
| + | One or more instances of the atom | ab+c | Abc | ac |
| ? | Zero or one instances of the atom | ab?c | ac, abc | abbc |
| {n} | n instances of the atom | ab{2}c | Abbc | abbbc |
| {n,} | At least n instances of the atom | ab{2,} | abbc, abbbc | abc |
| {n,m} | At least n, most m instances of the atom | ab{2,3}c | Abbc | abbbbcat |
Special Characters
Several special characters are denoted by backslashed letters. The following table lists the special characters.
Regular-Expression Special Characters
| Symbol | Matches | Example | Matches | Doesn't Match |
|---|---|---|---|---|
| \d | Any digit | b\dd | b4d | Bad |
| \D | Nondigit | b\Dd | bdd | b4d |
| \w | Alphanumeric character | a\wb | a2b | a_b |
| \W | Nonalphanumeric character | a\Wb | aa^b | Aabb |
Backslash, followed by any other character used to represent this character itself in the string. \&, for example, matches the & character.