dbCGI
Formula Expressions
These formula expressions can be used in evaluate directives and in an evaluate condition in an if directive.
You can refer to form variables by name alone inside a formula expression, provided the variable name starts with a letter or the underscore ("_"), and contains only letters, digits and the underscore. You can still refer to other variables using the formatting escapes, provided the substitution would result in valid syntax for the formula expressions..
The common arithmetic operators (+, -, *, /) and comparison operators (=, <>, !=, >, >=, <=) are available, as well as the following:
| Operator | Usage | Description |
|---|---|---|
| \ | string \ n | take the leftmost n characters from the string. |
| $ | string $ n | take the rightmost n characters from the string. |
| \\ | string1 \\ string2 | take the portion of string1 before the first occurrence of one of the characters in string2. |
| $$ | string1 $$ string2 | take the portion of string1 after the last occurrence of one of the characters in string2. |
| // | string1 // string2 | return the location of the first occurrence of one of the characters in string2 found in string1. |
| ?? | string1 ?? string2 | return the location of the last occurrence of one of the characters in string2 found in string1. |
| $ | string $ n | take the rightmost n characters from the string. |
| : | string1 : string2 | take string1, with all characters in string2 trimmed from the right hand side. |
| # | string # string | concatenate the strings. |
| ? | ?string | take the length of the string. |
| | | integer | integer | bitwise or. |
| & | integer & integer | bitwise and. |
| ^ | integer ^ integer | bitwise exclusive or. |
| ~ | ~integer | bitwise not. |
| ! | !integer | boolean not (0 becomes 1, everything else becomes 0). |
Boolean expressions return 1 for true and 0 for false.
It is strongly recommended that you put spaces around operators - future versions of dbCGI may include new operators formed by using more than one operator character from the existing set of operator characters.
Evaluation precedence is as follows, from highest to lowest:
-
Unary operators (~, !, ?)
-
Substring operators (\, $)
-
String Concatenation (#)
-
Multiplication and division (*, /)
-
Addition and subtraction (+, -)
-
Boolean comparison operators (=, <>, !=, >, >=, <=)
-
Bitwise boolean operators (|, &, ^)
The order of evaluation can be overridden by using parenthises - "(...)".
Literal strings can be inserted into expressions by enclosing them in either single or double quote characters.