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UNIX in a Nutshell: System V Edition

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Nroff and Troff
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.if

.if [!]condition anything

If condition is true, do anything. The presence of an ! negates the condition. If anything runs over more than one line, it can be delimited by \{ and \}.

Conditions

o

True if the page number is odd.

e

True if the page number is even.

n

True if the processor is nroff.

t

True if the processor is troff.

"str1"str2"

True if str1 is identical to str2. Often used to test the value of arguments passed to a macro.

expr

True if the value of expression expr is greater than zero.

Expressions

Expressions typically contain number register interpolations, and can use any of the following operators:

+ -

Addition, subtraction.

/ *

Multiplication, division.

%

Modulo.

> <

Greater than, less than.

>= <=

Greater than or equal, less than or equal.

= ==

Equal.

&

Logical AND.

:

Logical OR.

Examples

.if t .nr PD 0.5v  \" Set spacing between ms paragraphs
.if !"\\$2"" \{\ \" If the arg 2 is non null, print arg 3 in bold
\fB\\$2/\P\}


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