Leaders (The GNU Troff Manual)

#### 5.12.1 Leaders

Sometimes it is desirable to fill a tab stop with a given glyph, but also use tab stops normally on the same output line. An example is a table of contents entry that uses dots to bridge the entry name with its page number, which is itself aligned between tab stops. The `roff` language provides leaders for this purpose.67

A leader character (ISO and EBCDIC code point 1, also known as SOH or “start of heading”), behaves similarly to a tab character: it moves to the next tab stop. The difference is that for this movement, the default fill character is a period ‘`.`’.

Escape sequence: `\a``` ¶

  Interpolate a leader in copy mode; see Copy Mode.

Request: `.lc` [c] ¶

  Set the leader repetition character to the ordinary or special character c. Recall Tabs and Leaders: when encountering a leader character in the input, the formatter writes as many dots ‘`.`’ as are necessary until reaching the next tab stop; this is the leader definition character. Omitting c unsets the leader character. With no argument, GNU `troff` treats leaders the same as tabs. The leader repetition character is associated with the environment (see Environments). Only a single c is recognized; any excess is ignored.

A table of contents, for example, may define tab stops after a section number, a title, and a gap to be filled with leader dots. The page number follows the leader, after a right-aligned final tab stop wide enough to house the largest page number occurring in the document.

    .ds entry1 19.\tThe Prophet\a\t98
    .ds entry2 20.\tAll Astir\a\t101
    .ta .5i 4.5i +.5iR
    .nf
    \*[entry1]
    \*[entry2]
        ⇒ 19.  The Prophet.............................   98
        ⇒ 20.  All Astir...............................  101