Tabs and Fields (The GNU Troff Manual)

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5.12 Tabs and Fields

+ + + + +

A tab character (ISO code point 9, EBCDIC +code point 5) causes a horizontal movement to the next tab stop, if +any. +

Escape sequence: \t ¶: + + + + + +
Interpolate a tab in copy mode; see Copy Mode. +

+ +

Request: .ta [[n1 n2 … nn ]T r1 r2 … rn] ¶

Change tab stop positions. This request takes a series of tab +specifiers as arguments (optionally divided into two groups with the +letter ‘T’) that indicate where each tab stop is to be, overriding +any previous settings. The default scaling unit is ‘m’. Invoking +ta without an argument removes all tab stops. + + +GNU troff’s startup value is ‘T 0.5i’. +

Tab stops can be specified absolutely—as distances from the left +margin. The following example sets six tab stops, one every inch. +

.ta 1i 2i 3i 4i 5i 6i
+

+ +

Tab stops can also be specified using a leading ‘+’, which means +that the specified tab stop is set relative to the previous tab stop. +For example, the following is equivalent to the previous example. +

.ta 1i +1i +1i +1i +1i +1i
+

+ +

GNU troff supports an extended syntax to specify repeating tab +stops. These stops appear after a ‘T’ argument. Their values are +always taken as distances relative to the previous tab stop. This is +the idiomatic way to specify tab stops at equal intervals in +groff. The following is, yet again, the same as the previous +examples. It does more, in fact, since it defines an infinite number of +tab stops at one-inch intervals. +

.ta T 1i
+

+ +

Now we are ready to interpret the full syntax given above. The +ta request sets tabs at positions n1, n2, …, +nn, then at nn+r1, nn+r2, …, +nn+rn, then at nn+rn+r1, +nn+rn+r2, …, nn+rn+rn, and so +on. +

For example, ‘4c +6c T 3c 5c 2c’ is equivalent to ‘4c 10c 13c +18c 20c 23c 28c 30c …’. +

Text written to a tab column (i.e., between two tab stops, or between a +tab stop and an output line boundary) may be aligned to the right or +left, or centered in the column. This alignment is determined by +appending ‘R’, ‘L’, or ‘C’ to the tab specifier. The +default is ‘L’. +

.ta 1i 2iC 3iR
+

+ +

The beginning of an output line is not a tab stop; the text that begins +an output line is placed according to the configured alignment and +indentation; see Manipulating Filling and Adjustment and Line Layout. +

A tab stop is converted into a non-breakable horizontal movement that +cannot be adjusted. +

.ll 2i
+.ds foo a\tb\tc
+.ta T 1i
+\*[foo]
+    error→ warning: cannot break line
+    ⇒ a         b         c
+

+ +

The above creates a single output line that is a bit longer than two +inches (we use a string to show exactly where the tab stops are). +Now consider the following. +

.ll 2i
+.ds bar a\tb c\td
+.ta T 1i
+\*[bar]
+    error→ warning: cannot adjust line
+    ⇒ a         b
+    ⇒ c       d
+

+ +

GNU troff first converts the line’s tab stops into unbreakable +horizontal movements, then breaks after ‘b’. This usually isn’t +what you want. +

Superfluous tab characters—those that do not correspond to a tab +stop—are ignored except for the first, which delimits the characters +belonging to the last tab stop for right-alignment or centering. +

.ds Z   foo\tbar\tbaz
+.ds ZZ  foo\tbar\tbazqux
+.ds ZZZ foo\tbar\tbaz\tqux
+.ta 2i 4iR
+\*[Z]
+.br
+\*[ZZ]
+.br
+\*[ZZZ]
+.br
+    ⇒ foo                 bar              baz
+    ⇒ foo                 bar           bazqux
+    ⇒ foo                 bar              bazqux
+

+ +

The first line right-aligns “baz” within the second tab stop. The +second line right-aligns “bazqux” within it. The third line +right-aligns only “baz” because of the additional tab character, which +marks the end of the text occupying the last tab stop defined. +

Tab stops are associated with the environment (see Environments). +

+ + + +

The read-only register .tabs contains a string +representation of the current tab settings suitable for use as an +argument to the ta request.⁶⁶ +

.ds tab-string \n[.tabs]
+\*[tab-string]
+    ⇒ T120u
+

+ +

Request: .tc [c] ¶: + + + +
Set the tab repetition character to the ordinary or special character +c; normally, no glyph is written when moving to a tab stop (and +some output devices may output space characters to achieve this motion). +A tab repetition character causes the formatter to write as many +instances of c as are necessary to occupy the interval from the +horizontal drawing position to the next tab stop. With no argument, GNU +troff reverts to the default behavior. The tab repetition +character is associated with the environment (see Environments). +Only a single character of c is recognized; any excess is ignored. +

+ +

Request: .linetabs n ¶

+ + + +

If n is missing or non-zero, activate line-tabs; deactivate +it otherwise (the default). Active line-tabs cause GNU troff +to compute tab distances relative to the start of the output line +instead of the input line. +

.de Tabs
+.  ds x a\t\c
+.  ds y b\t\c
+.  ds z c
+.  ta 1i 3i
+\\*x
+\\*y
+\\*z
+..
+.Tabs
+.br
+.linetabs
+.Tabs
+    ⇒ a         b         c
+    ⇒ a         b                   c
+

+ +

Line-tabs activation is associated with the environment +(see Environments). The read-only register .linetabs +interpolates 1 if line-tabs are active, and 0 otherwise. +

+ + + +

Leaders
Fields