-tabs(1)tabs(1)
+tabs(1) General Commands Manual tabs(1)
@@ -59,13 +60,25 @@
absent, tabs is unable to clear/set tab-stops. The terminal should be
configured to use hard tabs, e.g.,
- stty tab0
+ stty tab0
Like clear(1), tabs writes to the standard output. You can redirect
the standard output to a file (which prevents tabs from actually chang-
ing the tabstops), and later cat the file to the screen, setting tab-
stops at that point.
+ These are hardware tabs, which cannot be queried rapidly by applica-
+ tions running in the terminal, if at all. Curses and other full-screen
+ applications may use hardware tabs in optimizing their output to the
+ terminal. If the hardware tabstops differ from the information in the
+ terminal database, the result is unpredictable. Before running curses
+ programs, you should either reset tab-stops to the standard interval
+
+ tabs -8
+
+ or use the reset program, since the normal initialization sequences do
+ not ensure that tab-stops are reset.
+
@@ -107,13 +120,13 @@
greater than zero. They are separated by a comma or a blank, for exam-
ple,
- tabs 1,6,11,16,21
- tabs 1 6 11 16 21
+ tabs 1,6,11,16,21
+ tabs 1 6 11 16 21
Use a "+" to treat a number as an increment relative to the previous
value, e.g.,
- tabs 1,+5,+5,+5,+5
+ tabs 1,+5,+5,+5,+5
which is equivalent to the 1,6,11,16,21 example.
@@ -141,30 +154,59 @@
- IEEE Std 1003.1/The Open Group Base Specifications Issue 7
+ IEEEStd1003.1/TheOpenGroupBaseSpecificationsIssue7
(POSIX.1-2008) describes a tabs utility. However
o This standard describes a +m option, to set a terminal's left-mar-
- gin. Very few of the entries in the terminal database provide this
- capability.
+ gin. Very few of the entries in the terminal database provide the
+ smgl (set_left_margin) or smglp (set_left_margin_parm) capability
+ needed to support the feature.
- o There is no counterpart in X/Open Curses Issue 7 for this utility,
+ o There is no counterpart in X/Open Curses Issue 7 for this utility,
unlike tput(1).
- The -d (debug) and -n (no-op) options are extensions not provided by
+ The -d (debug) and -n (no-op) options are extensions not provided by
other implementations.
- Documentation for other implementations states that there is a limit on
- the number of tab stops. While some terminals may not accept an arbi-
- trary 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.
+ A tabs utility appeared in PWB/Unix 1.0 (1977). There was a reduced
+ version of the tabs 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 tabs utility, which was included in System III (1980),
+ used built-in tables rather than the terminal database, to support a
+ half-dozen terminal 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, as a fallback. In an earlier develop-
+ ment effort, the tab-stop initialization provided by tset (1982) and
+ incorporated into tput uses the terminal database,
+
+ 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 tabs 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 Rationale section of the POSIX documentation goes into some detail
+ about the ways the committee considered redesigning the tabs and tput
+ 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 ExplicitLists described in this manual page were imple-
+ mented in PWB/Unix. Those provide the capability of setting abitrary
+ tab stops.
tset(1), infocmp(1m), curses(3x), terminfo(5).
- This describes ncurses version 6.0 (patch 20170603).
+ This describes ncurses version 6.2 (patch 20200425).