- The tabs program clears and sets tab-stops on the termi-
- nal. This uses the terminfo clear_all_tabs and set_tab
- capabilities. If either is absent, tabs is unable to
- clear/set tab-stops. The terminal should be configured to
- use hard tabs, e.g.,
+ The tabs program clears and sets tab-stops on the terminal. This uses
+ the terminfo clear_all_tabs and set_tab capabilities. If either is
+ 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 changing the tabstops), and later cat
- the file to the screen, setting tabstops at that point.
+ Like clear(1), tabs writes to the standard output. You can redirect
+ 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 not set, it will use the
- ansi+tabs entry.
+ 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, marked with
- asterisks.
+ -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 option, but not to modify the terminal
- settings.
+ -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.
+ -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 list to be processed.
+ 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
+ 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 to the right margin of the
- screen.
+ 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.
@@ -107,18 +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 example,
+ 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 value, e.g.,
+ 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.
@@ -146,35 +155,63 @@
- IEEE Std 1003.1/The Open Group Base Specifications Issue
- 7 (POSIX.1-2008) describes a tabs utility. However
+ IEEEStd1003.1/TheOpenGroupBaseSpecificationsIssue7
+ (POSIX.1-2008) describes a tabs utility. However
+
+ 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).
+
+ The -d (debug) and -n (no-op) options are extensions not provided by
+ other implementations.
+
+ 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,
- o This standard describes a +m option, to set a termi-
- nal's left-margin. Very few of the entries in the
- terminal database provide this capability.
+ 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.
- o There is no counterpart in X/Open Curses Issue 7 for
- this utility, unlike tput(1).
+ 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
- The -d (debug) and -n (no-op) options are extensions not
- provided by other implementations.
+ no known historical version of tabs supports the capability of
+ setting arbitrary tab stops.
- Documentation for other implementations states that there
- is a limit on the number of tab stops. While some termi-
- nals 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.
+ However, the ExplicitLists described in this manual page were
+ implemented in PWB/Unix. Those provide the capability of setting
+ abitrary tab stops.