- The <STRONG>-d</STRONG> (debug) and <STRONG>-n</STRONG> (no-op) options are extensions not provided by
- other implementations.
-
- A <STRONG>tabs</STRONG> utility appeared in PWB/Unix 1.0 (1977). There was a reduced
- version of the <STRONG>tabs</STRONG> utility in Unix 7th edition and in 3BSD (1979).
- The latter supported a single "-n" option (to cause the first tab stop
- to be set on the left margin). That option is not documented by POSIX.
-
- The PWB/Unix <STRONG>tabs</STRONG> utility, which was included in System III (1980),
- used built-in tables rather than the terminal database, to support a
- half-dozen hardcopy terminal (printer) types. It also had built-in
- logic to support the left-margin, as well as a feature for copying the
- tab settings from a file.
-
- Later versions of Unix, e.g., SVr4, added support for the terminal
- database, but kept the tables to support the printers. In an earlier
- development effort, the tab-stop initialization provided by <STRONG>tset</STRONG> (1982)
- and incorporated into <STRONG>tput</STRONG> uses the terminal database,
-
- The <STRONG>+m</STRONG> option was documented in the Base Specifications Issue 5
- (Unix98, 1997), and omitted in Issue 6 (Unix03, 2004) without
- documenting the rationale, though an introductory comment <EM>"and</EM>
- <EM>optionally</EM> <EM>adjusts</EM> <EM>the</EM> <EM>margin"</EM> remains, overlooked in the removal. The
- documented <STRONG>tabs</STRONG> utility in Issues 6 and later has no mechanism for
- setting margins. The <STRONG>+m</STRONG> option in this implementation differs from the
- feature in SVr4 by using terminal capabilities rather than built-in
- tables.
-
- POSIX documents no limits on the number of tab stops. Documentation
- for other implementations states that there is a limit on the number of
- tab stops (e.g., 20 in PWB/Unix's <STRONG>tabs</STRONG> utility). While some terminals
- may not accept an arbitrary number of tab stops, this implementation
- will attempt to set tab stops up to the right margin of the screen, if
- the given list happens to be that long.
-
- The <EM>Rationale</EM> section of the POSIX documentation goes into some detail
- about the ways the committee considered redesigning the <STRONG>tabs</STRONG> and <STRONG>tput</STRONG>
- utilities, without proposing an improved solution. It comments that
-
- no known historical version of tabs supports the capability of
- setting arbitrary tab stops.
-
- However, the <EM>Explicit</EM> <EM>Lists</EM> described in this manual page were
- implemented in PWB/Unix. Those provide the capability of setting
- abitrary tab stops.