if else endif $?x text1 $| text2 $. if x is defined if x is not defined
This expression yields one of two possible values:
if the macro named
x has a value,
text2 if it
The entire above expression, starting with the
ending with the
$., yields a single value, which
may contain multiple tokens.
The following, for example, includes
the configuration-file version
in the SMTP greeting message but does so only if
that version (in
$v; see Section 31.10.38) is defined:
O SmtpGreetingMessage=$j Sendmail ($v/
$?Z$Z$|generic$.) ready at $b note
Here the parenthetical version information is expressed one
Z has a value (like
but is expressed differently if
Z lacks a value:
The else part (
of this conditional expression is optional.
If it is omitted, the result is the same as if the
Both of the preceding yield the same result. If
x has a value, then
text1 becomes the value of the entire expression. If
lacks a value, then the entire expression lacks a value (produces
Note that it is not advisable to use the
conditional expression in rules. It may not have the
intended effect, because macro conditionals
are expanded when the configuration file is read.
$?x $?y both $| xonly $. $| $?y yonly $| none $. $.
This is just like the example in the previous section:
$?x text1 $| text2 $.
text2 are both conditionals:
text1 = $?y both $| xonly $. text2 = $?y yonly $| none $.
The grouping when conditionals nest is from the outside in. In the following example, parentheses have been inserted to show the groupings (they are not a part of either expression):
($?y both $| xonly $.
($?y yonly $| none $.
Interpretation is from left to right.
The logic of the second line above is therefore this:
have values, the result is
$x has a value
$y lacks one, the result is
lacks a value but
$y has one, the result is
And if both lack values, the result is
The sendmail program does not enforce or check for balance
in nested conditionals. Each
$? should have a corresponding
$. to balance it. If they do not balance, sendmail
will not detect the problem. Instead, it may interpret the
expression in a way that you did not intend.
The depth to which conditionals may be nested is limited only by our ability to easily comprehend the result. More than two deep is not recommended, and more than three deep is vigorously discouraged.