#### 37.6.2 Understanding operands and operators

Operands for macro expressions

An operand can be any of the following:

- a macro variable: $$name (see §37.3 Using macro variables)
- a number, including hexadecimal numbers starting with 0x or 0X
- a double-quoted string: "..."
- a single-quoted string: '...'
- a single-quoted character, including '\r' and '\n'
- an unquoted single word
- a parenthesized expression.

Operators for macro expressions

Operators include essentially the whole C-language numeric and logical sets, as well as some DITA2Go string operators; Table 37-6 shows the operators you can use in macro expressions. Most operators participate in binary (two-operand) expressions. Exceptions are the operators used in the ternary conditional expression described in §37.6.4.2 Using conditional expressions, and the unary string operators described in §37.6.5 Specifying substrings in expressions.

Table 37-6 Operators for HTML macro expressions

Type | Operator | Meaning | Comments
Relational |
    =, ==
| equal to | The result is 0 (zero) or 1 (one). Spaces are optional; you can use any number of spaces around symbol operators.
    !=, <>
| not equal to
    <
| less than
    <=
| less than or equal to
    >
| greater than
    >=
| greater than or equal to
Logical |
    and, &&
| both operands are true | The result is 0 (zero) or 1 (one). Two-word operators must have exactly one space between the two words. You can use any number of spaces elsewhere. Unlike in C, both operands are always fully evaluated.
    and not, &&!
| first is true, and second is false
    or, ||
| either is true, or both are true
    or not, ||!
| first is true, or second is false
    xor, ^
| one operand is true, the other is false
    xor not, ^!
| both are true, or both are false
Bitwise |
    &
| 1 where both operands have 1 0 everywhere else | These are numeric string operators. The first six are like the logical operators. The last two are bitwise shifts with the second operand the count. For example: (($$myvar >> 8) & 0xFF) extracts the second-up byte from a number.
    &~
| 1 where first has 1 and second has 0 0 everywhere else
    |
| 1 where either has or both have 1 0 where both operands have 0
    |~
| 1 where first has 1 or second has 0 0 where first has 0 and second has 1
    ^
| 1 where operand bits differ 0 where operand bits are the same
    ^~
| 1 where operand bits are the same 0 where operand bits differ
    << N
| shift first operand to the left N bits
    >> N
| shift first operand to the right N bits
Arithmetic |
    +
| plus | These are the usual suspects. The result of (n / 0) or (n % 0) is 0 (zero), because infinity is hard to represent.
    -
| minus
    *
| times
    /
| divided by
    %
| modulo
String |
    is
| equal to | is and is not are caseless compares using stricmp() plus is like strcat() before and after use strstr() to find the 2nd operand in the 1st: (doggie before gi) is dog You can get a strnicmp() effect using “first N” or “last N” with “is” or “is not”: (($$myvar first 3) is ($$yourvar last 3))
    is not
| not equal to
    plus
| concatenated with
    before
| substring before the 1st (leftmost) occurrence of 2nd string in 1st
    after
| substring after the first (leftmost) occurrence of 2nd string in 1st
    first N
| leftmost N characters (default = 1)
    last N
| rightmost N characters (default = 1)
    length
| length in characters | Integer result
    starts $$str
| true if $$str is at the start | Boolean result
    ends $$str
| true if $$str is at the end | Boolean result
    contains $$str
| true if $$str occurs anywhere in the string | Boolean result
    char N
| Nth character, counting from left | First (leftmost) character is number 1 Default value of N is 1
    trim first N
| all but first N characters | Default value of N is 1
    trim last N
| all but last N characters | Default value of N is 1
    $$str lower
| converts $$str to lowercase |
    $$str upper
| converts $$str to uppercase |
    $$str replace
    $$str1 with
    $$str2
| converts each instance of $$str1 in $$str to $$str2 |
Conditional |
    ?
| “if” the 1st operand is true, “then” the 2nd operand is the value of the expression | <$($$myvar ? "yes" : "no")> is equivalent to: <$_if ($$myvar)> yes <$_else> no <$_endif>
    :
| “else” the 3rd operand is the value of the expression

Previous Topic: 37.6.1 Understanding macro expressions

Next Topic: 37.6.3 Displaying expression results in output

Parent Topic: 37.6 Using expressions in macros

Sibling Topics:

37.6.1 Understanding macro expressions

37.6.3 Displaying expression results in output

37.6.4 Using control structures in expressions

37.6.5 Specifying substrings in expressions

37.6.6 Using list variables in expressions

37.6.7 Using indirection in expressions

37.6.8 Removing spaces from strings: an example

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