1tabs(1) General Commands Manual tabs(1)
2
6 tabs - set tabs on a terminal
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9 tabs [options]] [tabstop-list]
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12 The tabs program clears and sets tab-stops on the terminal. This uses
13 the terminfo clear_all_tabs and set_tab capabilities. If either is ab‐
14 sent, tabs is unable to clear/set tab-stops. The terminal should be
15 configured to use hard tabs, e.g.,
16 stty tab0
18 Like clear(1), tabs writes to the standard output. You can redirect
20 the standard output to a file (which prevents tabs from actually chang‐
21 ing the tabstops), and later cat the file to the screen, setting tab‐
22 stops at that point.
23 These are hardware tabs, which cannot be queried rapidly by applica‐
25 tions running in the terminal, if at all. Curses and other full-screen
26 applications may use hardware tabs in optimizing their output to the
27 terminal. If the hardware tabstops differ from the information in the
28 terminal database, the result is unpredictable. Before running curses
29 programs, you should either reset tab-stops to the standard interval
30 tabs -8
32 or use the reset program, since the normal initialization sequences do
34 not ensure that tab-stops are reset.
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37 General Options
38 -Tname
39 Tell tabs which terminal type to use. If this option is not
40 given, tabs will use the $TERM environment variable. If that is
41 not set, it will use the ansi+tabs entry.
42 -d The debugging option shows a ruler line, followed by two data
44 lines. The first data line shows the expected tab-stops marked
45 with asterisks. The second data line shows the actual tab-stops,
46 marked with asterisks.
47 -n This option tells tabs to check the options and run any debugging
49 option, but not to modify the terminal settings.
50 -V reports the version of ncurses which was used in this program, and
52 exits.
53 The tabs program processes a single list of tab stops. The last option
55 to be processed which defines a list is the one that determines the
56 list to be processed.
57 Implicit Lists
59 Use a single number as an option, e.g., “-5” to set tabs at the given
60 interval (in this case 1, 6, 11, 16, 21, etc.). Tabs are repeated up
61 to the right margin of the screen.
62 Use “-0” to clear all tabs.
64 Use “-8” to set tabs to the standard interval.
66 Explicit Lists
68 An explicit list can be defined after the options (this does not use a
69 “-”). The values in the list must be in increasing numeric order, and
70 greater than zero. They are separated by a comma or a blank, for exam‐
71 ple,
72 tabs 1,6,11,16,21
74 tabs 1 6 11 16 21
75 Use a “+” to treat a number as an increment relative to the previous
77 value, e.g.,
78 tabs 1,+5,+5,+5,+5
80 which is equivalent to the 1,6,11,16,21 example.
82 Predefined Tab-Stops
84 POSIX defines several predefined lists of tab stops.
85 -a Assembler, IBM S/370, first format
87 1,10,16,36,72
88 -a2 Assembler, IBM S/370, second format
90 1,10,16,40,72
91 -c COBOL, normal format
93 1,8,12,16,20,55
94 -c2 COBOL compact format
96 1,6,10,14,49
97 -c3 COBOL compact format extended
99 1,6,10,14,18,22,26,30,34,38,42,46,50,54,58,62,67
100 -f FORTRAN
102 1,7,11,15,19,23
103 -p PL/I
105 1,5,9,13,17,21,25,29,33,37,41,45,49,53,57,61
106 -s SNOBOL
108 1,10,55
109 -u UNIVAC 1100 Assembler
111 1,12,20,44
112 Margins
114 A few terminals provide the capability for changing their left/right
115 margins. The tabs program has an option to use this feature:
116 +m margin
118 The effect depends on whether the terminal has the margin capabil‐
119 ities:
120 • If the terminal provides the capability for setting the left
122 margin, tabs uses this, and adjusts the available width for
123 tab-stops.
124 • If the terminal does not provide the margin capabilities, tabs
126 imitates the effect, putting the tab stops at the appropriate
127 place on each line. The terminal's left-margin is not modi‐
128 fied.
129 If the margin parameter is omitted, the default is 10. Use +m0 to
131 reset the left margin, i.e., to the left edge of the terminal's
132 display. Before setting a left-margin, tabs resets the margin to
133 reduce problems which might arise on moving the cursor before the
134 current left-margin.
135 When setting or resetting the left-margin, tabs may reset the right-
137 margin.
138
140 IEEE Std 1003.1/The Open Group Base Specifications Issue 7
141 (POSIX.1-2008) describes a tabs utility. However
142 • This standard describes a +m option, to set a terminal's left-mar‐
144 gin. Very few of the entries in the terminal database provide the
145 smgl (set_left_margin) or smglp (set_left_margin_parm) capability
146 needed to support the feature.
147 • There is no counterpart in X/Open Curses Issue 7 for this utility,
149 unlike tput(1).
150 The -d (debug) and -n (no-op) options are extensions not provided by
152 other implementations.
153 A tabs utility appeared in PWB/Unix 1.0 (1977). There was a reduced
155 version of the tabs utility in Unix 7th edition and in 3BSD (1979).
156 The latter supported a single “-n” option (to cause the first tab stop
157 to be set on the left margin). That option is not documented by POSIX.
158 The PWB/Unix tabs utility, which was included in System III (1980),
160 used built-in tables rather than the terminal database, to support a
161 half-dozen hardcopy terminal (printer) types. It also had built-in
162 logic to support the left-margin, as well as a feature for copying the
163 tab settings from a file.
164 Later versions of Unix, e.g., SVr4, added support for the terminal
166 database, but kept the tables to support the printers. In an earlier
167 development effort, the tab-stop initialization provided by tset (1982)
168 and incorporated into tput uses the terminal database,
169 The +m option was documented in the Base Specifications Issue 5
171 (Unix98, 1997), and omitted in Issue 6 (Unix03, 2004) without document‐
172 ing the rationale, though an introductory comment “and optionally ad‐
173 justs the margin” remains, overlooked in the removal. The documented
174 tabs utility in Issues 6 and later has no mechanism for setting mar‐
175 gins. The +m option in this implementation differs from the feature in
176 SVr4 by using terminal capabilities rather than built-in tables.
177 POSIX documents no limits on the number of tab stops. Documentation
179 for other implementations states that there is a limit on the number of
180 tab stops (e.g., 20 in PWB/Unix's tabs utility). While some terminals
181 may not accept an arbitrary number of tab stops, this implementation
182 will attempt to set tab stops up to the right margin of the screen, if
183 the given list happens to be that long.
184 The Rationale section of the POSIX documentation goes into some detail
186 about the ways the committee considered redesigning the tabs and tput
187 utilities, without proposing an improved solution. It comments that
188 no known historical version of tabs supports the capability of
190 setting arbitrary tab stops.
191 However, the Explicit Lists described in this manual page were imple‐
193 mented in PWB/Unix. Those provide the capability of setting abitrary
194 tab stops.
195
197 infocmp(1M), tset(1), curses(3X), terminfo(5).
198 This describes ncurses version 6.4 (patch 20230520).
200 tabs(1)