sendmail, 4th Edition

Macro Expansion: $ and $&

The value of a macro can be used by putting a $ character in front of the macro’s name. For example, consider the following definition:

DXtext

Here, the macro named X is given text as its value.

If you later prefix a macro name with a $ character, you can use that value. This is called expanding a macro:

$X

Here, the expression $X tells sendmail to use the value stored in X (the text) rather than its name (X).

For multicharacter names, the process is the same, but the name is surrounded with curly braces:

D{Xxx}text         ← declare {Xxx}
${Xxx}             ← use {Xxx}