gtroff has most arithmetic operators common to other languages:
gtroff only provides integer arithmetic. The internal type used
for computing results is ‘int’, which is usually a 32-bit signed
whilerequests).10 See below for the use of unary operators in motion requests.
The logical not operator,
as described above,
works only within
Furthermore, it may appear
only at the beginning of an expression,
and negates the entire expression.
Attempting to insert the ‘!’ operator
within the expression results in a
‘numeric expression expected’ warning. This
with old versions of
.nr X 1 .nr Y 0 .\" This does not work as expected .if (\n[X])&(!\n[Y]) .nop X only . .\" Use this construct instead .if (\n[X]=1)&(\n[Y]=0) .nop X only
.nr x 5 .nr y 3 .nr z (\n[x] >? \n[y])
z now contains 5.
(c;e). Evaluate e using c as the default scaling indicator. If c is missing, ignore scaling indicators in the evaluation of e.
Parentheses may be used as in any other language. However, in
gtroff they are necessary to ensure order of evaluation.
gtroff has no operator precedence; expressions are evaluated left
to right. This means that
gtroff evaluates ‘3+5*4’ as if it
were parenthesized like ‘(3+5)*4’, not as ‘3+(5*4)’, as might
For many requests that cause a motion on the page, the unary operators ‘+’ and ‘-’ work differently if leading an expression. They then indicate a motion relative to the current position (down or up, respectively).
Similarly, a leading ‘|’ operator indicates an absolute position. For vertical movements, it specifies the distance from the top of the page; for horizontal movements, it gives the distance from the beginning of the input line.
‘+’ and ‘-’ are also treated differently by the following
requests and escapes:
Here, leading plus and minus signs indicate increments and decrements.
See Setting Registers, for some examples.
Return 1 if anything is a valid numeric expression; or 0 if anything is empty or not a valid numeric expression.
Due to the way arguments are parsed, spaces are not allowed in expressions, unless the entire expression is surrounded by parentheses.
See Request and Macro Arguments, and Conditionals and Loops.