1MORE(1P) POSIX Programmer's Manual MORE(1P)
2
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 more - display files on a page-by-page basis
13
15 more [-ceisu][-n number][-p command][-t tagstring][file ...]
16
18 The more utility shall read files and either write them to the terminal
19 on a page-by-page basis or filter them to standard output. If standard
20 output is not a terminal device, all input files shall be copied to
21 standard output in their entirety, without modification, except as
22 specified for the -s option. If standard output is a terminal device,
23 the files shall be written a number of lines (one screenful) at a time
24 under the control of user commands. See the EXTENDED DESCRIPTION sec‐
25 tion.
26 Certain block-mode terminals do not have all the capabilities necessary
28 to support the complete more definition; they are incapable of accept‐
29 ing commands that are not terminated with a <newline>. Implementations
30 that support such terminals shall provide an operating mode to more in
31 which all commands can be terminated with a <newline> on those termi‐
32 nals. This mode:
33 * Shall be documented in the system documentation
35 * Shall, at invocation, inform the user of the terminal deficiency
37 that requires the <newline> usage and provide instructions on how
38 this warning can be suppressed in future invocations
39 * Shall not be required for implementations supporting only fully
41 capable terminals
42 * Shall not affect commands already requiring <newline>s
44 * Shall not affect users on the capable terminals from using more as
46 described in this volume of IEEE Std 1003.1-2001
47
49 The more utility shall conform to the Base Definitions volume of
50 IEEE Std 1003.1-2001, Section 12.2, Utility Syntax Guidelines.
51 The following options shall be supported:
53 -c If a screen is to be written that has no lines in common with
55 the current screen, or more is writing its first screen, more
56 shall not scroll the screen, but instead shall redraw each line
57 of the screen in turn, from the top of the screen to the bottom.
58 In addition, if more is writing its first screen, the screen
59 shall be cleared. This option may be silently ignored on devices
60 with insufficient terminal capabilities.
61 -e By default, more shall exit immediately after writing the last
63 line of the last file in the argument list. If the -e option is
64 specified:
65 1. If there is only a single file in the argument list and that
67 file was completely displayed on a single screen, more shall
68 exit immediately after writing the last line of that file.
69 2. Otherwise, more shall exit only after reaching end-of-file
71 on the last file in the argument list twice without an
72 intervening operation. See the EXTENDED DESCRIPTION section.
73 -i Perform pattern matching in searches without regard to case; see
75 the Base Definitions volume of IEEE Std 1003.1-2001, Section
76 9.2, Regular Expression General Requirements.
77 -n number
79 Specify the number of lines per screenful. The number argument
80 is a positive decimal integer. The -n option shall override any
81 values obtained from any other source.
82 -p command
84 Each time a screen from a new file is displayed or redisplayed
85 (including as a result of more commands; for example, :p), exe‐
86 cute the more command(s) in the command arguments in the order
87 specified, as if entered by the user after the first screen has
88 been displayed. No intermediate results shall be displayed (that
89 is, if the command is a movement to a screen different from the
90 normal first screen, only the screen resulting from the command
91 shall be displayed.) If any of the commands fail for any reason,
92 an informational message to this effect shall be written, and no
93 further commands specified using the -p option shall be executed
94 for this file.
95 -s Behave as if consecutive empty lines were a single empty line.
97 -t tagstring
99 Write the screenful of the file containing the tag named by the
100 tagstring argument. See the ctags utility. The tags feature rep‐
101 resented by -t tagstring and the :t command is optional. It
102 shall be provided on any system that also provides a conforming
103 implementation of ctags; otherwise, the use of -t produces unde‐
104 fined results.
105 The filename resulting from the -t option shall be logically added as a
107 prefix to the list of command line files, as if specified by the user.
108 If the tag named by the tagstring argument is not found, it shall be an
109 error, and more shall take no further action.
110 If the tag specifies a line number, the first line of the display shall
112 contain the beginning of that line. If the tag specifies a pattern, the
113 first line of the display shall contain the beginning of the matching
114 text from the first line of the file that contains that pattern. If the
115 line does not exist in the file or matching text is not found, an
116 informational message to this effect shall be displayed, and more shall
117 display the default screen as if -t had not been specified.
118 If both the -t tagstring and -p command options are given, the -t
120 tagstring shall be processed first; that is, the file and starting line
121 for the display shall be as specified by -t, and then the -p more com‐
122 mand shall be executed. If the line (matching text) specified by the -t
123 command does not exist (is not found), no -p more command shall be exe‐
124 cuted for this file at any time.
125 -u Treat a <backspace> as a printable control character, displayed
127 as an implementation-defined character sequence (see the
128 EXTENDED DESCRIPTION section), suppressing backspacing and the
129 special handling that produces underlined or standout mode text
130 on some terminal types. Also, do not ignore a <carriage-return>
131 at the end of a line.
132
135 The following operand shall be supported:
136 file A pathname of an input file. If no file operands are specified,
138 the standard input shall be used. If a file is '-', the standard
139 input shall be read at that point in the sequence.
140
143 The standard input shall be used only if no file operands are speci‐
144 fied, or if a file operand is '-' .
145
147 The input files being examined shall be text files. If standard output
148 is a terminal, standard error shall be used to read commands from the
149 user. If standard output is a terminal, standard error is not readable,
150 and command input is needed, more may attempt to obtain user commands
151 from the controlling terminal (for example, /dev/tty); otherwise, more
152 shall terminate with an error indicating that it was unable to read
153 user commands. If standard output is not a terminal, no error shall
154 result if standard error cannot be opened for reading.
155
157 The following environment variables shall affect the execution of more:
158 COLUMNS
160 Override the system-selected horizontal display line size. See
161 the Base Definitions volume of IEEE Std 1003.1-2001, Chapter 8,
162 Environment Variables for valid values and results when it is
163 unset or null.
164 EDITOR Used by the v command to select an editor. See the EXTENDED
166 DESCRIPTION section.
167 LANG Provide a default value for the internationalization variables
169 that are unset or null. (See the Base Definitions volume of
170 IEEE Std 1003.1-2001, Section 8.2, Internationalization Vari‐
171 ables for the precedence of internationalization variables used
172 to determine the values of locale categories.)
173 LC_ALL If set to a non-empty string value, override the values of all
175 the other internationalization variables.
176 LC_COLLATE
178 Determine the locale for the behavior of ranges, equivalence
180 classes, and multi-character collating elements within regular
181 expressions.
182 LC_CTYPE
184 Determine the locale for the interpretation of sequences of
185 bytes of text data as characters (for example, single-byte as
186 opposed to multi-byte characters in arguments and input files)
187 and the behavior of character classes within regular expres‐
188 sions.
189 LC_MESSAGES
191 Determine the locale that should be used to affect the format
192 and contents of diagnostic messages written to standard error
193 and informative messages written to standard output.
194 NLSPATH
196 Determine the location of message catalogs for the processing of
197 LC_MESSAGES .
198 LINES Override the system-selected vertical screen size, used as the
200 number of lines in a screenful. See the Base Definitions volume
201 of IEEE Std 1003.1-2001, Chapter 8, Environment Variables for
202 valid values and results when it is unset or null. The -n option
203 shall take precedence over the LINES variable for determining
204 the number of lines in a screenful.
205 MORE Determine a string containing options described in the OPTIONS
207 section preceded with hyphens and <blank>-separated as on the
208 command line. Any command line options shall be processed after
209 those in the MORE variable, as if the command line were:
210 more $MORE options operands
213 The MORE variable shall take precedence over the TERM and LINES vari‐
215 ables for determining the number of lines in a screenful.
216 TERM Determine the name of the terminal type. If this variable is
218 unset or null, an unspecified default terminal type is used.
219
222 Default.
223
225 The standard output shall be used to write the contents of the input
226 files.
227
229 The standard error shall be used for diagnostic messages and user com‐
230 mands (see the INPUT FILES section), and, if standard output is a ter‐
231 minal device, to write a prompting string. The prompting string shall
232 appear on the screen line below the last line of the file displayed in
233 the current screenful. The prompt shall contain the name of the file
234 currently being examined and shall contain an end-of-file indication
235 and the name of the next file, if any, when prompting at the end-of-
236 file. If an error or informational message is displayed, it is unspeci‐
237 fied whether it is contained in the prompt. If it is not contained in
238 the prompt, it shall be displayed and then the user shall be prompted
239 for a continuation character, at which point another message or the
240 user prompt may be displayed. The prompt is otherwise unspecified. It
241 is unspecified whether informational messages are written for other
242 user commands.
243
245 None.
246
248 The following section describes the behavior of more when the standard
249 output is a terminal device. If the standard output is not a terminal
250 device, no options other than -s shall have any effect, and all input
251 files shall be copied to standard output otherwise unmodified, at which
252 time more shall exit without further action.
253 The number of lines available per screen shall be determined by the -n
255 option, if present, or by examining values in the environment (see the
256 ENVIRONMENT VARIABLES section). If neither method yields a number, an
257 unspecified number of lines shall be used.
258 The maximum number of lines written shall be one less than this number,
260 because the screen line after the last line written shall be used to
261 write a user prompt and user input. If the number of lines in the
262 screen is less than two, the results are undefined. It is unspecified
263 whether user input is permitted to be longer than the remainder of the
264 single line where the prompt has been written.
265 The number of columns available per line shall be determined by examin‐
267 ing values in the environment (see the ENVIRONMENT VARIABLES section),
268 with a default value as described in the Base Definitions volume of
269 IEEE Std 1003.1-2001, Chapter 8, Environment Variables.
270 Lines that are longer than the display shall be folded; the length at
272 which folding occurs is unspecified, but should be appropriate for the
273 output device. Folding may occur between glyphs of single characters
274 that take up multiple display columns.
275 When standard output is a terminal and -u is not specified, more shall
277 treat <backspace>s and <carriage-return>s specially:
278 * A character, followed first by a sequence of n <backspace>s (where n
280 is the same as the number of column positions that the character
281 occupies), then by n underscore characters ( '_' ), shall cause that
282 character to be written as underlined text, if the terminal type
283 supports that. The n underscore characters, followed first by n
284 <backspace>s, then any character with n column positions, shall also
285 cause that character to be written as underlined text, if the termi‐
286 nal type supports that.
287 * A sequence of n <backspace>s (where n is the same as the number of
289 column positions that the previous character occupies) that appears
290 between two identical printable characters shall cause the first of
291 those two characters to be written as emboldened text (that is, vis‐
292 ually brighter, standout mode, or inverse-video mode), if the termi‐
293 nal type supports that, and the second to be discarded. Immediately
294 subsequent occurrences of <backspace>/ character pairs for that same
295 character shall also be discarded. (For example, the sequence
296 "a\ba\ba\ba" is interpreted as a single emboldened 'a' .)
297 * The more utility shall logically discard all other <backspace>s from
299 the line as well as the character which precedes them, if any.
300 * A <carriage-return> at the end of a line shall be ignored, rather
302 than being written as a non-printable character, as described in the
303 next paragraph.
304 It is implementation-defined how other non-printable characters are
306 written. Implementations should use the same format that they use for
307 the ex print command; see the OPTIONS section within the ed utility. It
308 is unspecified whether a multi-column character shall be separated if
309 it crosses a display line boundary; it shall not be discarded. The
310 behavior is unspecified if the number of columns on the display is less
311 than the number of columns any single character in the line being dis‐
312 played would occupy.
313 When each new file is displayed (or redisplayed), more shall write the
315 first screen of the file. Once the initial screen has been written,
316 more shall prompt for a user command. If the execution of the user com‐
317 mand results in a screen that has lines in common with the current
318 screen, and the device has sufficient terminal capabilities, more shall
319 scroll the screen; otherwise, it is unspecified whether the screen is
320 scrolled or redrawn.
321 For all files but the last (including standard input if no file was
323 specified, and for the last file as well, if the -e option was not
324 specified), when more has written the last line in the file, more shall
325 prompt for a user command. This prompt shall contain the name of the
326 next file as well as an indication that more has reached end-of-file.
327 If the user command is f, <control>-F, <space>, j, <newline>, d, <con‐
328 trol>-D, or s, more shall display the next file. Otherwise, if display‐
329 ing the last file, more shall exit. Otherwise, more shall execute the
330 user command specified.
331 Several of the commands described in this section display a previous
333 screen from the input stream. In the case that text is being taken from
334 a non-rewindable stream, such as a pipe, it is implementation-defined
335 how much backwards motion is supported. If a command cannot be executed
336 because of a limitation on backwards motion, an error message to this
337 effect shall be displayed, the current screen shall not change, and the
338 user shall be prompted for another command.
339 If a command cannot be performed because there are insufficient lines
341 to display, more shall alert the terminal. If a command cannot be per‐
342 formed because there are insufficient lines to display or a / command
343 fails: if the input is the standard input, the last screen in the file
344 may be displayed; otherwise, the current file and screen shall not
345 change, and the user shall be prompted for another command.
346 The interactive commands in the following sections shall be supported.
348 Some commands can be preceded by a decimal integer, called count in the
349 following descriptions. If not specified with the command, count shall
350 default to 1. In the following descriptions, pattern is a basic regular
351 expression, as described in the Base Definitions volume of
352 IEEE Std 1003.1-2001, Section 9.3, Basic Regular Expressions. The term
353 "examine" is historical usage meaning "open the file for viewing''; for
354 example, more foo would be expressed as examining file foo.
355 In the following descriptions, unless otherwise specified, line is a
357 line in the more display, not a line from the file being examined.
358 In the following descriptions, the current position refers to two
360 things:
361 1. The position of the current line on the screen
363 2. The line number (in the file) of the current line on the screen
365 Usually, the line on the screen corresponding to the current position
367 is the third line on the screen. If this is not possible (there are
368 fewer than three lines to display or this is the first page of the
369 file, or it is the last page of the file), then the current position is
370 either the first or last line on the screen as described later.
371 Help
373 Synopsis:
374 h
377 Write a summary of these commands and other implementation-defined com‐
380 mands. The behavior shall be as if the more utility were executed with
381 the -e option on a file that contained the summary information. The
382 user shall be prompted as described earlier in this section when end-
383 of-file is reached. If the user command is one of those specified to
384 continue to the next file, more shall return to the file and screen
385 state from which the h command was executed.
386 Scroll Forward One Screenful
388 Synopsis:
389 [count]f
392 [count]<control>-F
393 Scroll forward count lines, with a default of one screenful. If count
396 is more than the screen size, only the final screenful shall be writ‐
397 ten.
398 Scroll Backward One Screenful
400 Synopsis:
401 [count]b
404 [count]<control>-B
405 Scroll backward count lines, with a default of one screenful (see the
408 -n option). If count is more than the screen size, only the final
409 screenful shall be written.
410 Scroll Forward One Line
412 Synopsis:
413 [count]<space>
416 [count]j
417 [count]<newline>
418 Scroll forward count lines. The default count for the <space> shall be
421 one screenful; for j and <newline>, one line. The entire count lines
422 shall be written, even if count is more than the screen size.
423 Scroll Backward One Line
425 Synopsis:
426 [count]k
429 Scroll backward count lines. The entire count lines shall be written,
432 even if count is more than the screen size.
433 Scroll Forward One Half Screenful
435 Synopsis:
436 [count]d
439 [count]<control>-D
440 Scroll forward count lines, with a default of one half of the screen
443 size. If count is specified, it shall become the new default for subse‐
444 quent d, <control>-D, and u commands.
445 Skip Forward One Line
447 Synopsis:
448 [count]s
451 Display the screenful beginning with the line count lines after the
454 last line on the current screen. If count would cause the current posi‐
455 tion to be such that less than one screenful would be written, the last
456 screenful in the file shall be written.
457 Scroll Backward One Half Screenful
459 Synopsis:
460 [count]u
463 [count]<control>-U
464 Scroll backward count lines, with a default of one half of the screen
467 size. If count is specified, it shall become the new default for subse‐
468 quent d, <control>-D, u, and <control>-U commands. The entire count
469 lines shall be written, even if count is more than the screen size.
470 Go to Beginning of File
472 Synopsis:
473 [count]g
476 Display the screenful beginning with line count.
479 Go to End-of-File
481 Synopsis:
482 [count]G
485 If count is specified, display the screenful beginning with the line
488 count. Otherwise, display the last screenful of the file.
489 Refresh the Screen
491 Synopsis:
492 r
495 <control>-L
496 Refresh the screen.
499 Discard and Refresh
501 Synopsis:
502 R
505 Refresh the screen, discarding any buffered input. If the current file
508 is non-seekable, buffered input shall not be discarded and the R com‐
509 mand shall be equivalent to the r command.
510 Mark Position
512 Synopsis:
513 mletter
516 Mark the current position with the letter named by letter, where letter
519 represents the name of one of the lowercase letters of the portable
520 character set. When a new file is examined, all marks may be lost.
521 Return to Mark
523 Synopsis:
524 'letter
527 Return to the position that was previously marked with the letter named
530 by letter, making that line the current position.
531 Return to Previous Position
533 Synopsis:
534 ''
537 Return to the position from which the last large movement command was
540 executed (where a "large movement" is defined as any movement of more
541 than a screenful of lines). If no such movements have been made, return
542 to the beginning of the file.
543 Search Forward for Pattern
545 Synopsis:
546 [count]/[!]pattern<newline>
549 Display the screenful beginning with the countth line containing the
552 pattern. The search shall start after the first line currently dis‐
553 played. The null regular expression ( '/' followed by a <newline>)
554 shall repeat the search using the previous regular expression, with a
555 default count. If the character '!' is included, the matching lines
556 shall be those that do not contain the pattern. If no match is found
557 for the pattern, a message to that effect shall be displayed.
558 Search Backward for Pattern
560 Synopsis:
561 [count]?[!]pattern<newline>
564 Display the screenful beginning with the countth previous line contain‐
567 ing the pattern. The search shall start on the last line before the
568 first line currently displayed. The null regular expression ( '?' fol‐
569 lowed by a <newline>) shall repeat the search using the previous regu‐
570 lar expression, with a default count. If the character '!' is included,
571 matching lines shall be those that do not contain the pattern. If no
572 match is found for the pattern, a message to that effect shall be dis‐
573 played.
574 Repeat Search
576 Synopsis:
577 [count]n
580 Repeat the previous search for countth line containing the last pattern
583 (or not containing the last pattern, if the previous search was "/!" or
584 "?!" ).
585 Repeat Search in Reverse
587 Synopsis:
588 [count]N
591 Repeat the search in the opposite direction of the previous search for
594 the countth line containing the last pattern (or not containing the
595 last pattern, if the previous search was "/!" or "?!" ).
596 Examine New File
598 Synopsis:
599 :e [filename]<newline>
602 Examine a new file. If the filename argument is not specified, the cur‐
605 rent file (see the :n and :p commands below) shall be re-examined. The
606 filename shall be subjected to the process of shell word expansions
607 (see Word Expansions ); if more than a single pathname results, the
608 effects are unspecified. If filename is a number sign ( '#' ), the
609 previously examined file shall be re-examined. If filename is not
610 accessible for any reason (including that it is a non-seekable file),
611 an error message to this effect shall be displayed and the current file
612 and screen shall not change.
613 Examine Next File
615 Synopsis:
616 [count]:n
619 Examine the next file. If a number count is specified, the countth next
622 file shall be examined. If filename refers to a non-seekable file, the
623 results are unspecified.
624 Examine Previous File
626 Synopsis:
627 [count]:p
630 Examine the previous file. If a number count is specified, the countth
633 previous file shall be examined. If filename refers to a non-seekable
634 file, the results are unspecified.
635 Go to Tag
637 Synopsis:
638 :t tagstring<newline>
641 If the file containing the tag named by the tagstring argument is not
644 the current file, examine the file, as if the :e command was executed
645 with that file as the argument. Otherwise, or in addition, display the
646 screenful beginning with the tag, as described for the -t option (see
647 the OPTIONS section). If the ctags utility is not supported by the
648 system, the use of :t produces undefined results.
649 Invoke Editor
651 Synopsis:
652 v
655 Invoke an editor to edit the current file being examined. If standard
658 input is being examined, the results are unspecified. The name of the
659 editor shall be taken from the environment variable EDITOR , or shall
660 default to vi. If the last pathname component in EDITOR is either vi or
661 ex, the editor shall be invoked with a -c linenumber command line argu‐
662 ment, where linenumber is the line number of the file line containing
663 the display line currently displayed as the first line of the screen.
664 It is implementation-defined whether line-setting options are passed to
665 editors other than vi and ex.
666 When the editor exits, more shall resume with the same file and screen
668 as when the editor was invoked.
669 Display Position
671 Synopsis:
672 =
675 <control>-G
676 Write a message for which the information references the first byte of
679 the line after the last line of the file on the screen. This message
680 shall include the name of the file currently being examined, its number
681 relative to the total number of files there are to examine, the line
682 number in the file, the byte number and the total bytes in the file,
683 and what percentage of the file precedes the current position. If more
684 is reading from standard input, or the file is shorter than a single
685 screen, the line number, the byte number, the total bytes, and the per‐
686 centage need not be written.
687 Quit
689 Synopsis:
690 q
693 :q
694 ZZ
695 Exit more.
698
700 The following exit values shall be returned:
701 0 Successful completion.
703 >0 An error occurred.
705
708 If an error is encountered accessing a file when using the :n command,
709 more shall attempt to examine the next file in the argument list, but
710 the final exit status shall be affected. If an error is encountered
711 accessing a file via the :p command, more shall attempt to examine the
712 previous file in the argument list, but the final exit status shall be
713 affected. If an error is encountered accessing a file via the :e com‐
714 mand, more shall remain in the current file and the final exit status
715 shall not be affected.
716 The following sections are informative.
718
720 When the standard output is not a terminal, only the -s filter-modifi‐
721 cation option is effective. This is based on historical practice. For
722 example, a typical implementation of man pipes its output through more
723 -s to squeeze excess white space for terminal users. When man is piped
724 to lp, however, it is undesirable for this squeezing to happen.
725
727 The -p allows arbitrary commands to be executed at the start of each
728 file. Examples are:
729 more -p G file1 file2
731 Examine each file starting with its last screenful.
733 more -p 100 file1 file2
735 Examine each file starting with line 100 in the current position
737 (usually the third line, so line 98 would be the first line
738 written).
739 more -p /100 file1 file2
741 Examine each file starting with the first line containing the
743 string "100" in the current position
744
747 The more utility, available in BSD and BSD-derived systems, was chosen
748 as the prototype for the POSIX file display program since it is more
749 widely available than either the public-domain program less or than pg,
750 a pager provided in System V. The 4.4 BSD more is the model for the
751 features selected; it is almost fully upwards-compatible from the 4.3
752 BSD version in wide use and has become more amenable for vi users.
753 Several features originally derived from various file editors, found in
754 both less and pg, have been added to this volume of
755 IEEE Std 1003.1-2001 as they have proved extremely popular with users.
756 There are inconsistencies between more and vi that result from histori‐
758 cal practice. For example, the single-character commands h, f, b, and
759 <space> are screen movers in more, but cursor movers in vi. These
760 inconsistencies were maintained because the cursor movements are not
761 applicable to more and the powerful functionality achieved without the
762 use of the control key justifies the differences.
763 The tags interface has been included in a program that is not a text
765 editor because it promotes another degree of consistent operation with
766 vi. It is conceivable that the paging environment of more would be
767 superior for browsing source code files in some circumstances.
768 The operating mode referred to for block-mode terminals effectively
770 adds a <newline> to each Synopsis line that currently has none. So, for
771 example, d <newline> would page one screenful. The mode could be trig‐
772 gered by a command line option, environment variable, or some other
773 method. The details are not imposed by this volume of
774 IEEE Std 1003.1-2001 because there are so few systems known to support
775 such terminals. Nevertheless, it was considered that all systems should
776 be able to support more given the exception cited for this small commu‐
777 nity of terminals because, in comparison to vi, the cursor movements
778 are few and the command set relatively amenable to the optional <new‐
779 line>s.
780 Some versions of more provide a shell escaping mechanism similar to the
782 ex ! command. The standard developers did not consider that this was
783 necessary in a paginator, particularly given the wide acceptance of
784 multiple window terminals and job control features. (They chose to
785 retain such features in the editors and mailx because the shell inter‐
786 action also gives an opportunity to modify the editing buffer, which is
787 not applicable to more.)
788 The -p (position) option replaces the + command because of the Utility
790 Syntax Guidelines. In early proposals, it took a pattern argument, but
791 historical less provided the more general facility of a command. It
792 would have been desirable to use the same -c as ex and vi, but the let‐
793 ter was already in use.
794 The text stating "from a non-rewindable stream ... implementations may
796 limit the amount of backwards motion supported" would allow an imple‐
797 mentation that permitted no backwards motion beyond text already on the
798 screen. It was not possible to require a minimum amount of backwards
799 motion that would be effective for all conceivable device types. The
800 implementation should allow the user to back up as far as possible,
801 within device and reasonable memory allocation constraints.
802 Historically, non-printable characters were displayed using the ARPA
804 standard mappings, which are as follows:
805 1. Printable characters are left alone.
807 2. Control characters less than \177 are represented as followed by
809 the character offset from the '@' character in the ASCII map; for
810 example, \007 is represented as 'G' .
811 3. \177 is represented as followed by '?' .
813 The display of characters having their eighth bit set was less stan‐
815 dard. Existing implementations use hex (0x00), octal (\000), and a
816 meta-bit display. (The latter displayed characters with their eighth
817 bit set as the two characters "M-", followed by the seven-bit display
818 as described previously.) The latter probably has the best claim to
819 historical practice because it was used with the -v option of 4 BSD and
820 4 BSD-derived versions of the cat utility since 1980.
821 No specific display format is required by IEEE Std 1003.1-2001. Imple‐
823 mentations are encouraged to conform to historic practice in the
824 absence of any strong reason to diverge.
825
827 None.
828
830 Shell Command Language, ctags, ed, ex, vi
831
833 Portions of this text are reprinted and reproduced in electronic form
834 from IEEE Std 1003.1, 2003 Edition, Standard for Information Technology
835 -- Portable Operating System Interface (POSIX), The Open Group Base
836 Specifications Issue 6, Copyright (C) 2001-2003 by the Institute of
837 Electrical and Electronics Engineers, Inc and The Open Group. In the
838 event of any discrepancy between this version and the original IEEE and
839 The Open Group Standard, the original IEEE and The Open Group Standard
840 is the referee document. The original Standard can be obtained online
841 at http://www.opengroup.org/unix/online.html .
842IEEE/The Open Group 2003 MORE(1P)