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Sendmail, 3rd Edition by Bryan Costales

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Option Argument Types

The second column of Table 24-4 shows the type of the argument for each option. The allowable types are the following:

Boolean

A Boolean-type argument can have only one of two possible values: true or false. If the Boolean argument is present, its first letter is compared to the four letters T, t, Y, and y. If that first letter matches any of those four, the option is set to true; otherwise, it is set to false. If a Boolean argument is absent, the option defaults to true. For example:

O HoldExpensive          Boolean absent, option is set to true.
O HoldExpensive=True     Boolean=`T'rue, option is set to true.
O HoldExpensive=False Boolean=`F'alse, option is set tofalse.
Character

A character type is a single ASCII character. Options that take a single character as an argument can also take a whole word or sentence, but in that instance, only the first character is recognized:

O DeliveryMode=b         b for background mode
O DeliveryMode=background same

The argument is case-sensitive—that is, the character b is considered to be different from the character B:

O DeliveryMode=b         b for background mode
O DeliveryMode=B meaningless
Numeric

A numeric type is an ASCII representation of an integer value. It can be positive, zero, or negative. The base is determined after any leading sign is handled. A leading 0 causes the octal base to be used. A leading 0x or 0X causes the hexadecimal base to be used. Decimal is best to use for options such as the hop count (option MaxHopCount): ...

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