-tabs(1)tabs(1)
+tabs(1) General Commands Manual tabs(1)
@@ -59,41 +60,54 @@
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.
+ the standard output to a file (which prevents tabs from actually
+ changing the tabstops), and later cat the file to the screen, setting
+ tabstops at that point.
+
+ These are hardware tabs, which cannot be queried rapidly by
+ applications 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.
-Tname
- Tell tabs which terminal type to use. If this option is not
- given, tabs will use the $TERM environment variable. If that is
+ Tell tabs which terminal type to use. If this option is not
+ given, tabs will use the $TERM environment variable. If that is
not set, it will use the ansi+tabs entry.
- -d The debugging option shows a ruler line, followed by two data
- lines. The first data line shows the expected tab-stops marked
- with asterisks. The second data line shows the actual tab-stops,
+ -d The debugging option shows a ruler line, followed by two data
+ lines. The first data line shows the expected tab-stops marked
+ with asterisks. The second data line shows the actual tab-stops,
marked with asterisks.
- -n This option tells tabs to check the options and run any debugging
+ -n This option tells tabs to check the options and run any debugging
option, but not to modify the terminal settings.
-V reports the version of ncurses which was used in this program, and
exits.
The tabs program processes a single list of tab stops. The last option
- to be processed which defines a list is the one that determines the
+ to be processed which defines a list is the one that determines the
list to be processed.
- Use a single number as an option, e.g., "-5" to set tabs at the given
- interval (in this case 1, 6, 11, 16, 21, etc.). Tabs are repeated up
+ Use a single number as an option, e.g., "-5" to set tabs at the given
+ interval (in this case 1, 6, 11, 16, 21, etc.). Tabs are repeated up
to the right margin of the screen.
Use "-0" to clear all tabs.
@@ -102,18 +116,18 @@
- An explicit list can be defined after the options (this does not use a
- "-"). The values in the list must be in increasing numeric order, and
- greater than zero. They are separated by a comma or a blank, for exam-
- ple,
+ An explicit list can be defined after the options (this does not use a
+ "-"). The values in the list must be in increasing numeric order, and
+ greater than zero. They are separated by a comma or a blank, for
+ example,
- 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
+ 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.
@@ -141,12 +155,13 @@
- 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.
+ o This standard describes a +m option, to set a terminal's left-
+ margin. 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,
unlike tput(1).
@@ -154,17 +169,45 @@
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
+ development 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
+ implemented in PWB/Unix. Those provide the capability of setting
+ abitrary tab stops.