1UNEXPAND(1P) POSIX Programmer's Manual UNEXPAND(1P)
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6 This manual page is part of the POSIX Programmer's Manual. The Linux
7 implementation of this interface may differ (consult the corresponding
8 Linux manual page for details of Linux behavior), or the interface may
9 not be implemented on Linux.
10
12 unexpand — convert spaces to tabs
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15 unexpand [-a|-t tablist] [file...]
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18 The unexpand utility shall copy files or standard input to standard
19 output, converting <blank> characters at the beginning of each line
20 into the maximum number of <tab> characters followed by the minimum
21 number of <space> characters needed to fill the same column positions
22 originally filled by the translated <blank> characters. By default,
23 tabstops shall be set at every eighth column position. Each <backspace>
24 shall be copied to the output, and shall cause the column position
25 count for tab calculations to be decremented; the count shall never be
26 decremented to a value less than one.
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29 The unexpand utility shall conform to the Base Definitions volume of
30 POSIX.1‐2017, Section 12.2, Utility Syntax Guidelines.
31 The following options shall be supported:
33 -a In addition to translating <blank> characters at the begin‐
35 ning of each line, translate all sequences of two or more
36 <blank> characters immediately preceding a tab stop to the
37 maximum number of <tab> characters followed by the minimum
38 number of <space> characters needed to fill the same column
39 positions originally filled by the translated <blank> charac‐
40 ters.
41 -t tablist
43 Specify the tab stops. The application shall ensure that the
44 tablist option-argument is a single argument consisting of a
45 single positive decimal integer or multiple positive decimal
46 integers, separated by <blank> or <comma> characters, in
47 ascending order. If a single number is given, tabs shall be
48 set tablist column positions apart instead of the default 8.
49 If multiple numbers are given, the tabs shall be set at those
50 specific column positions.
51 The application shall ensure that each tab-stop position N is
53 an integer value greater than zero, and the list shall be in
54 strictly ascending order. This is taken to mean that, from
55 the start of a line of output, tabbing to position N shall
56 cause the next character output to be in the (N+1)th column
57 position on that line. When the -t option is not specified,
58 the default shall be the equivalent of specifying -t 8
59 (except for the interaction with -a, described below).
60 No <space>-to-<tab> conversions shall occur for characters at
62 positions beyond the last of those specified in a multiple
63 tab-stop list.
64 When -t is specified, the presence or absence of the -a
66 option shall be ignored; conversion shall not be limited to
67 the processing of leading <blank> characters.
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70 The following operand shall be supported:
71 file A pathname of a text file to be used as input.
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75 See the INPUT FILES section.
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78 The input files shall be text files.
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81 The following environment variables shall affect the execution of unex‐
82 pand:
83 LANG Provide a default value for the internationalization vari‐
85 ables that are unset or null. (See the Base Definitions vol‐
86 ume of POSIX.1‐2017, Section 8.2, Internationalization Vari‐
87 ables for the precedence of internationalization variables
88 used to determine the values of locale categories.)
89 LC_ALL If set to a non-empty string value, override the values of
91 all the other internationalization variables.
92 LC_CTYPE Determine the locale for the interpretation of sequences of
94 bytes of text data as characters (for example, single-byte as
95 opposed to multi-byte characters in arguments and input
96 files), the processing of <tab> and <space> characters, and
97 for the determination of the width in column positions each
98 character would occupy on an output device.
99 LC_MESSAGES
101 Determine the locale that should be used to affect the format
102 and contents of diagnostic messages written to standard
103 error.
104 NLSPATH Determine the location of message catalogs for the processing
106 of LC_MESSAGES.
107
109 Default.
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112 The standard output shall be equivalent to the input files with the
113 specified <space>-to-<tab> conversions.
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116 The standard error shall be used only for diagnostic messages.
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119 None.
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122 None.
123
125 The following exit values shall be returned:
126 0 Successful completion.
128 >0 An error occurred.
130
132 Default.
133 The following sections are informative.
135
137 One non-intuitive aspect of unexpand is its restriction to leading
138 <space> characters when neither -a nor -t is specified. Users who
139 always want to convert all <space> characters in a file can easily
140 alias unexpand to use the -a or -t 8 option.
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143 None.
144
146 On several occasions, consideration was given to adding a -t option to
147 the unexpand utility to complement the -t in expand (see expand). The
148 historical intent of unexpand was to translate multiple <blank> charac‐
149 ters into tab stops, where tab stops were a multiple of eight column
150 positions on most UNIX systems. An early proposal omitted -t because it
151 seemed outside the scope of the User Portability Utilities option; it
152 was not described in any of the base documents for IEEE Std
153 1003.2‐1992. However, hard-coding tab stops every eight columns was
154 not suitable for the international community and broke historical
155 precedents for some vendors in the FORTRAN community, so -t was
156 restored in conjunction with the list of valid extension categories
157 considered by the standard developers. Thus, unexpand is now the logi‐
158 cal converse of expand.
159
161 None.
162
164 expand, tabs
165 The Base Definitions volume of POSIX.1‐2017, Chapter 8, Environment
167 Variables, Section 12.2, Utility Syntax Guidelines
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170 Portions of this text are reprinted and reproduced in electronic form
171 from IEEE Std 1003.1-2017, Standard for Information Technology -- Por‐
172 table Operating System Interface (POSIX), The Open Group Base Specifi‐
173 cations Issue 7, 2018 Edition, Copyright (C) 2018 by the Institute of
174 Electrical and Electronics Engineers, Inc and The Open Group. In the
175 event of any discrepancy between this version and the original IEEE and
176 The Open Group Standard, the original IEEE and The Open Group Standard
177 is the referee document. The original Standard can be obtained online
178 at http://www.opengroup.org/unix/online.html .
179 Any typographical or formatting errors that appear in this page are
181 most likely to have been introduced during the conversion of the source
182 files to man page format. To report such errors, see https://www.ker‐
183 nel.org/doc/man-pages/reporting_bugs.html .
184IEEE/The Open Group 2017 UNEXPAND(1P)