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30 .\" $Id: tabs.1,v 1.59 2024/04/20 19:08:15 tom Exp $
31 .TH @TABS@ 1 2024-04-20 "ncurses @NCURSES_MAJOR@.@NCURSES_MINOR@" "User commands"
50 set terminal tab stops
52 \fB@TABS@\fP [\fIoptions\fP] [\fItabstop-list\fP]
54 The \fB@TABS@\fP program clears and sets tab-stops on the terminal.
55 This uses the terminfo \fBclear_all_tabs\fP and \fBset_tab\fP capabilities.
56 If either is absent, \fB@TABS@\fP is unable to clear/set tab-stops.
57 The terminal should be configured to use hard tabs, e.g.,
65 Like \fB@CLEAR@\fP(1), \fB@TABS@\fP writes to the standard output.
66 You can redirect the standard output to a file (which prevents
67 \fB@TABS@\fP from actually changing the tabstops),
68 and later \fBcat\fP the file to the screen, setting tabstops at that point.
70 These are hardware tabs, which cannot be queried rapidly by applications
71 running in the terminal, if at all.
72 Curses and other full-screen applications may use hardware tabs
73 in optimizing their output to the terminal.
74 If the hardware tabstops differ from the information in the terminal
75 database, the result is unpredictable.
76 Before running curses programs,
77 you should either reset tab-stops to the standard interval
85 or use the \fB@RESET@\fP program,
86 since the normal initialization sequences do not ensure that tab-stops
92 Tell \fB@TABS@\fP which terminal type to use.
93 If this option is not given, \fB@TABS@\fP will use the \fB$TERM\fP
95 If that is not set, it will use the \fIansi+tabs\fP entry.
98 The debugging option shows a ruler line, followed by two data lines.
99 The first data line shows the expected tab-stops marked with asterisks.
100 The second data line shows the actual tab-stops, marked with asterisks.
103 This option tells \fB@TABS@\fP to check the options and run any debugging
104 option, but not to modify the terminal settings.
107 reports the version of \fI\%ncurses\fP which was used in this program,
110 The \fB@TABS@\fP program processes a single list of tab stops.
111 The last option to be processed which defines a list is the one that
112 determines the list to be processed.
114 Use a single number as an option,
115 e.g., \*(``\fB\-5\fP\*('' to set tabs at the given
116 interval (in this case 1, 6, 11, 16, 21, etc.).
117 Tabs are repeated up to the right margin of the screen.
119 Use \*(``\fB\-0\fP\*('' to clear all tabs.
121 Use \*(``\fB\-8\fP\*('' to set tabs to the standard interval.
123 An explicit list can be defined after the options
124 (this does not use a \*(``\-\*('').
125 The values in the list must be in increasing numeric order,
126 and greater than zero.
127 They are separated by a comma or a blank, for example,
136 Use a \*(``+\*('' to treat a number
137 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 expose a means of changing their left and right margins.
196 \fB@TABS@\fP supports this feature with an option.
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 \fB@TABS@\fP uses this,
204 and adjusts the available tab stop widths.
206 If the terminal does not provide the margin capabilities,
207 \fB@TABS@\fP imitates their effect,
208 putting tab stops at appropriate places on each line.
209 The terminal's left margin is not modified.
214 parameter is omitted,
218 to reset the left margin,
220 to make it the left edge of the terminal's display.
221 Before setting a left margin,
222 \fB@TABS@\fP resets the margin to reduce problems that might arise
223 from moving the cursor to the left of the current left margin.
225 When setting or resetting the left margin,
226 \fB@TABS@\fP may also reset the right margin.
230 tab stop initialization database
232 IEEE Std 1003.1/The Open Group Base Specifications Issue 7
239 this standard describes a
241 option to set a terminal's left margin.
242 Very few of the entries in the terminal database provide the
246 .B \%set_left_margin_parm
248 capabilities needed to support the feature.
250 There is no counterpart in X/Open Curses Issue 7 for this utility,
251 unlike \fB@TPUT@\fP(1).
259 extensions not provided by other implementations.
263 utility appeared in PWB/Unix 1.0 (1977).
264 .\" https://minnie.tuhs.org/cgi-bin/utree.pl?file=PWB1/sys/source/s2/\
266 A reduced version shipped in Seventh Edition Unix
268 .\" https://minnie.tuhs.org/cgi-bin/utree.pl?file=V7/usr/src/cmd/tabs.c
270 .\" https://minnie.tuhs.org/cgi-bin/utree.pl?file=3BSD/usr/src/cmd/\
272 (later the same year);
273 it supported a \*(``\-n\*('' option to set the first tab stop at the
275 That option is not specified by POSIX.
279 utility returned in System III (1980),
280 and used built-in tables
281 to support a half-dozen hardcopy terminal (printer) types.
282 It also had logic to support setting the left margin,
283 as well as a feature for copying the tab settings from a file.
285 Versions of the program in later releases of AT&T Unix,
287 .\" https://minnie.tuhs.org/cgi-bin/utree.pl?file=SysVR4/cmd/tabs/tabs.c
288 added support for the terminal database,
289 but retained the tables to support the printers.
293 had incorporated the tab stop initialization feature of BSD's
302 option was documented in the POSIX Base Specifications Issue 5
304 then omitted in Issue 6
306 without express motivation,
307 though an introductory comment
308 \*(``and optionally adjusts the margin\*('' remains,
309 overlooked in the removal.
312 utility documented in Issues 6 and later has no mechanism for setting
318 \fB\%@TABS@\fP differs from the SVr4 feature by using terminal
319 capabilities rather than built-in tables.
321 POSIX documents no limit on the number of tab stops.
322 Other implementations impose one;
323 the limit is 20 in PWB/Unix's
326 While some terminals may not accept an arbitrary number of tab stops,
328 \fB\%@TABS@\fP attempts to set tab stops up to the right margin if the
329 list thereof is sufficiently long.
331 The \*(``Rationale\*('' section of the Issue 6
334 .\" https://pubs.opengroup.org/onlinepubs/009604499/utilities/tabs.html
335 details how the committee considered redesigning the
340 without settling on an improved solution.
344 \*(``no known historical version of
346 supports the capability of setting arbitrary tab stops.\*(''
349 The feature described in subsection \*(``Explicit Lists\*('' above was
350 implemented in PWB/Unix,
352 and permitted the setting of abitrary tab stops nevertheless.
354 \fB\%@INFOCMP@\fP(1M),