UDM Command Format - Expressions

The following basic rules apply to expressions in UDM commands.

Delimiters

All expressions must be bound by left angle ( < ) and right angle ( > ) brackets.

For example:

set value=<2 + 2>

Operand / Operator Delimiters

Operands and operators in an expression must be separated by a space.

For example, the following is not legal:

<2+4>

There must be a space before and after the operator < + >:

<2 + 4>

Appearance

An expression can appear either as a parameter or its value. It must comprise the entire parameter or value in which it appears, not just part of it.

For example, in the following command, <2 + 2> is not an expression:

echo "2 + 2 = <2 + 2>"

It is merely part of the quoted string, and the output would be:

2 + 2 = <2 + 2>

In order to treat <2 + 2> as an expression, the command must be:

echo "2 + 2 = " <2 + 2>

The output of this command is:

2 + 2 = 4

Integer Only

Although floating point number are allowed in expressions, everything is evaluated as an integer. The only exception is that the EQ - Equal and NE - Not Equal comparators can be used to compare strings as well as numbers.

Operator Precedence

The operator order of precedence (and reading left to right) is:

1. NOT
2. *, /, and %
3. + and -
4. EQ, NE, LT, GT, LE, and GE
5. AND, OR, and XOR

To manually indicate that an operation is of higher precedence, enclose it in parentheses: ( and ). An expression is evaluated going from the inner most set of parentheses out. Sets on the same level are evaluated left to right.

The following examples illustrates how parentheses can affect results.

In the following expression, where < * > takes precedence over < + >:

<5 + 4 * 2>

The expression yields the following value:

13

However, when the expression includes the following parentheses:

<(5 + 4) * 2>

The expression yields the following value:

18

Nesting

Expressions can be nested in order to indicate desired change precedence. Nested expressions are bound by parentheses: ( and ).

When nested expressions are a part of an expression, the deepest nested portions are evaluated first. Also, spaces are not required between the ( and ) when they are used for nesting, as they are between operators and operands.

For example:

Operations

All operations take the following form:

left-value operator right-value

The left-value and right-value can be:

• Strings (EQ and NE only)
• Numbers
• Variable references
• Other operations

The following table identifies and describes all of the operators for UDM command expressions.