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30 .\" $Id: tabs.1,v 1.44 2023/09/16 23:38:39 tom Exp $
31 .TH @TABS@ 1 2023-09-16 "ncurses 6.4" "User commands"
62 set terminal tab stops
64 \fB@TABS@\fP [\fIoptions\fP]] \fI[tabstop-list]\fP
66 The \fB@TABS@\fP program clears and sets tab-stops on the terminal.
67 This uses the terminfo \fBclear_all_tabs\fP and \fBset_tab\fP capabilities.
68 If either is absent, \fB@TABS@\fP is unable to clear/set tab-stops.
69 The terminal should be configured to use hard tabs, e.g.,
74 Like \fB@CLEAR@\fP(1), \fB@TABS@\fP writes to the standard output.
75 You can redirect the standard output to a file (which prevents
76 \fB@TABS@\fP from actually changing the tabstops),
77 and later \fBcat\fP the file to the screen, setting tabstops at that point.
79 These are hardware tabs, which cannot be queried rapidly by applications
80 running in the terminal, if at all.
81 Curses and other full-screen applications may use hardware tabs
82 in optimizing their output to the terminal.
83 If the hardware tabstops differ from the information in the terminal
84 database, the result is unpredictable.
85 Before running curses programs,
86 you should either reset tab-stops to the standard interval
91 or use the \fB@RESET@\fP program,
92 since the normal initialization sequences do not ensure that tab-stops
98 Tell \fB@TABS@\fP which terminal type to use.
99 If this option is not given, \fB@TABS@\fP will use the \fB$TERM\fP
100 environment variable.
101 If that is not set, it will use the \fIansi+tabs\fP entry.
104 The debugging option shows a ruler line, followed by two data lines.
105 The first data line shows the expected tab-stops marked with asterisks.
106 The second data line shows the actual tab-stops, marked with asterisks.
109 This option tells \fB@TABS@\fP to check the options and run any debugging
110 option, but not to modify the terminal settings.
113 reports the version of ncurses which was used in this program, and exits.
115 The \fB@TABS@\fP program processes a single list of tab stops.
116 The last option to be processed which defines a list is the one that
117 determines the list to be processed.
119 Use a single number as an option,
120 e.g., \*(``\fB\-5\fP\*('' to set tabs at the given
121 interval (in this case 1, 6, 11, 16, 21, etc.).
122 Tabs are repeated up to the right margin of the screen.
124 Use \*(``\fB\-0\fP\*('' to clear all tabs.
126 Use \*(``\fB\-8\fP\*('' to set tabs to the standard interval.
128 An explicit list can be defined after the options
129 (this does not use a \*(``\-\*('').
130 The values in the list must be in increasing numeric order,
131 and greater than zero.
132 They are separated by a comma or a blank, for example,
139 Use a \*(``+\*('' to treat a number
140 as an increment relative to the previous value,
146 which is equivalent to the 1,6,11,16,21 example.
147 .SS Predefined Tab-Stops
148 POSIX defines several predefined lists of tab stops.
151 Assembler, IBM S/370, first format
156 Assembler, IBM S/370, second format
171 COBOL compact format extended
173 1,6,10,14,18,22,26,30,34,38,42,46,50,54,58,62,67
183 1,5,9,13,17,21,25,29,33,37,41,45,49,53,57,61
191 UNIVAC 1100 Assembler
195 A few terminals provide the capability for changing their left/right margins.
196 The @TABS@ program has an option to use this feature:
199 The effect depends on whether the terminal has the margin capabilities:
202 If the terminal provides the capability for setting the left margin,
203 @TABS@ uses this, and adjusts the available width for tab-stops.
205 If the terminal does not provide the margin capabilities,
206 @TABS@ imitates the effect, putting the tab stops at the appropriate
208 The terminal's left-margin is not modified.
211 If the \fImargin\fP parameter is omitted, the default is 10.
212 Use \fB+m0\fP to reset the left margin,
213 i.e., to the left edge of the terminal's display.
214 Before setting a left-margin,
215 @TABS@ resets the margin to reduce problems which might arise
216 on moving the cursor before the current left-margin.
218 When setting or resetting the left-margin,
219 @TABS@ may reset the right-margin.
221 \fIIEEE Std 1003.1/The Open Group Base Specifications Issue 7\fP (POSIX.1-2008)
222 describes a \fBtabs\fP utility.
225 This standard describes a \fB+m\fP option, to set a terminal's left-margin.
226 Very few of the entries in the terminal database provide the
227 \fBsmgl\fP (\fBset_left_margin\fP) or
228 \fBsmglp\fP (\fBset_left_margin_parm\fP)
229 capability needed to support the feature.
231 There is no counterpart in X/Open Curses Issue 7 for this utility,
232 unlike \fB@TPUT@\fP(1).
234 The \fB\-d\fP (debug) and \fB\-n\fP (no-op) options are extensions not provided
235 by other implementations.
237 A \fBtabs\fP utility appeared in PWB/Unix 1.0 (1977).
238 There was a reduced version of the \fBtabs\fP utility
239 in Unix 7th edition and in 3BSD (1979).
240 The latter supported a single \*(``\-n\*('' option
241 (to cause the first tab stop to be set on the left margin).
242 That option is not documented by POSIX.
244 The PWB/Unix \fBtabs\fP utility, which was included in System III (1980),
245 used built-in tables rather than the terminal database,
246 to support a half-dozen hardcopy terminal (printer) types.
247 It also had built-in logic to support the left-margin,
248 as well as a feature for copying the tab settings from a file.
250 Later versions of Unix, e.g., SVr4,
251 added support for the terminal database,
252 but kept the tables to support the printers.
253 In an earlier development effort,
254 the tab-stop initialization provided by \fBtset\fP (1982)
255 and incorporated into \fBtput\fP uses the terminal database,
257 The \fB+m\fP option was documented
258 in the Base Specifications Issue 5 (Unix98, 1997),
259 and omitted in Issue 6 (Unix03, 2004) without documenting the rationale,
260 though an introductory comment
261 \fI\*(``and optionally adjusts the margin\*(''\fP remains,
262 overlooked in the removal.
263 The documented \fBtabs\fP utility in Issues 6 and later has no mechanism
265 The \fB+m\fP option in this implementation differs from the feature
266 in SVr4 by using terminal capabilities rather than built-in tables.
268 POSIX documents no limits on the number of tab stops.
269 Documentation for other implementations states that there is a limit on the
271 (e.g., 20 in PWB/Unix's \fBtabs\fP utility).
272 While some terminals may not accept an arbitrary number
273 of tab stops, this implementation will attempt to set tab stops up to the
274 right margin of the screen, if the given list happens to be that long.
276 The \fIRationale\fP section of the POSIX documentation goes into some
277 detail about the ways the committee considered redesigning the
278 \fBtabs\fP and \fBtput\fP utilities,
279 without proposing an improved solution.
283 no known historical version of tabs supports the capability of setting
287 However, the \fIExplicit Lists\fP described in this manual page
288 were implemented in PWB/Unix.
289 Those provide the capability of setting abitrary tab stops.
296 This describes \fBncurses\fP
297 version @NCURSES_MAJOR@.@NCURSES_MINOR@ (patch @NCURSES_PATCH@).