Note: this page describes conditional expressions as used in ploticus #if statements.
are slightly different and are described
Conditional expressions use a simple syntax made up of operators such as = and !=,
operands, and logical connectors such as && and ||.
Operands may be literal numeric, alphanumeric, or text string values,
@variables, @data-fields, or
, literal string operands may be enclosed in double quotes (")
(but no quotes may be used in ploticus select: attributes)
There is no concept of precedence in these expressions (other than left to right);
parentheses cannot be used except within strings.
- In a
, see if the value of the variable @SUM is greater than 100:
#if @SUM > 100
- Another example:
#if @SUM > 100 && @STATUS = s
- Check to see if @description has any contents:
#if $len(@description) > 0
- Check to see if @val is a valid number:
#if $isnumber(@val) = 1
- See if @C does not countain a double quote:
#if @C != "\\""
Here's a conditional expression for finding lastname
beginning with Gr, Gu or Gy:
@lastname inlike Gr*,Gu*,Gy*
Operands may be
@field numbers, e.g. @1 = first data field
Literal values (numbers, alphanumerics, text strings,
, literal alphanumeric, text string, or
operands may be enclosed in double quotes (");
no variable evaluation occurs inside quoted strings.
= Equal to. This is case sensitive for strings.
!= Not equal to.
> Greater than.
>= Greater than or equal to.
< Less than.
<= Less than or equal to.
If at least one operand is non-numeric, comparison
operators such as > will do an ascii value comparison.
Wild card matching: Wild card matching may be done
using like. Wild card characters are * which matches
any number of any character, and ? which matches a single
instance of any character. This matching is case-insensitive.
like Wild card match. Example: hello like h* (true)
!like Not a wild card match.
Commalist operators: these take a
on the right side.
By default, lists are delimited using commas. If this is not convenient,
the list delimitation character may be changed using
in Member of list. Example: z in x,y,z (true)
!in Not a member of list. (Alt: ni)
inlike Same as in but wild card matching is used.
(Wild cards may be used in list members.)
!inlike Same as !in but wild card matching is used.
Individual conditional expressions may be connected together using
logical AND (&&) or OR (||).
An entire expression may be negated by putting not: at the beginning
of the expression.
Because parentheses may not be used to establish precedence
mixing AND and OR in the same expression requires care.
When the expression is parsed, it is first
split into OR terms, then each of the OR terms is split into AND terms.
For example: A = B and C = D or E = E of F = G would evaluate to true,
because it is interpreted as if it were written
(a = B and C = D) or (e = e) or (f = g).
It may be best to avoid mixing AND and OR in the same expression
and use multiple expressions instead.
Limitations and bugs
Because parentheses may not be used to establish precedence,
the mixing of AND and OR in the same expression is problematic (see above).