Auto-increment (The GNU Troff Manual)

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5.8.3 Auto-increment

+ + + + +

Registers can also be incremented or decremented by a configured amount +at the time they are interpolated. The value of the increment is +specified with a third argument to the nr request, and a special +interpolation syntax is used to alter and then retrieve the register’s +value. Together, these features are called +auto-increment.⁵¹ +

Request: .nr ident value incr ¶: + +
Set register ident to value and its auto-incrementation +amount to to incr. The \R escape sequence doesn’t support +an incr argument. +

+ +

Auto-incrementation is not completely automatic; the \n +escape sequence in its basic form never alters the value of a register. +To apply auto-incrementation to a register, interpolate it with +‘\n±’. +

Escape sequence: \n+i ¶: +
Escape sequence: \n-i ¶
Escape sequence: \n+(id ¶
Escape sequence: \n-(id ¶
Escape sequence: \n+[ident] ¶
Escape sequence: \n-[ident] ¶: Increment or decrement ident (one-character +name i, two-character name id) by the register’s +auto-incrementation value and then interpolate the new register value. +If ident has no auto-incrementation value, interpolate as with +\n. +

+ +

.nr a 0 1
+.nr xx 0 5
+.nr foo 0 -2
+\n+a, \n+a, \n+a, \n+a, \n+a
+.br
+\n-(xx, \n-(xx, \n-(xx, \n-(xx, \n-(xx
+.br
+\n+[foo], \n+[foo], \n+[foo], \n+[foo], \n+[foo]
+    ⇒ 1, 2, 3, 4, 5
+    ⇒ -5, -10, -15, -20, -25
+    ⇒ -2, -4, -6, -8, -10
+

+ + + +

To change the increment value without changing the value of a register, +assign the register’s value to itself by interpolating it, and specify +the desired increment normally. Apply an increment of ‘0’ to +disable auto-incrementation of the register. +

+ +