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Add Free Documentation License. New section

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"Overwrite Old Files", and revamp that section to make it easier to
follow.  "tar" -> "GNU tar" where appropriate.  Migrate getdate
documentation into getdate.texi.  Fix several minor typos.  Describe
TAR_OPTIONS.  Describe incompatibility between incremental backups and
--atime-preserve.  Describe incompatibility between --verify and other
options.  Mention that tar normally removes symbolic links rather than
following them, when extracting a file of the same name.
This commit is contained in:
Paul Eggert
2000-10-24 06:18:37 +00:00
parent e89bcb7fb3
commit ae2b051832
1 changed files with 126 additions and 494 deletions
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@@ -131,7 +131,7 @@
@set xref-blocking-factor @xref{Blocking Factor}
@set pxref-blocking-factor @pxref{Blocking Factor}
@set op-bzip2 @kbd{--bzip2} (@kbd{-I})
@set op-bzip2 @kbd{--bzip2} (@kbd{-j})
@set ref-bzip2 @ref{gzip}
@set xref-bzip2 @xref{gzip}
@set pxref-bzip2 @pxref{gzip}
@@ -196,7 +196,7 @@
@set xref-file @xref{file}
@set pxref-file @pxref{file}
@set op-files-from @kbd{--files-from=@var{file-of-names}} (@kbd{-T @var{file-of-names}})
@set op-files-from @kbd{--files-from=@var{file-of-names}} (@kbd{-I @var{file-of-names}}, @kbd{-T @var{file-of-names}})
@set ref-files-from @ref{files}
@set xref-files-from @xref{files}
@set pxref-files-from @pxref{files}
@@ -317,9 +317,9 @@
@set pxref-one-file-system @pxref{one}
@set op-overwrite @kbd{--overwrite}
@set ref-overwrite @ref{Writing}
@set xref-overwrite @xref{Writing}
@set pxref-overwrite @pxref{Writing}
@set ref-overwrite @ref{Overwrite Old Files}
@set xref-overwrite @xref{Overwrite Old Files}
@set pxref-overwrite @pxref{Overwrite Old Files}
@set op-owner @kbd{--owner=@var{user}}
@set ref-owner @ref{Option Summary}
@@ -474,28 +474,17 @@ Published by the Free Software Foundation,
59 Temple Place - Suite 330,
Boston, MA 02111-1307, USA
Copyright 1992, 1994, 1995, 1996, 1997, 1999 Free Software Foundation, Inc.
Copyright 1992, 1994, 1995, 1996, 1997, 1999, 2000 Free Software
Foundation, Inc.
Permission is granted to make and distribute verbatim copies of
this manual provided the copyright notice and this permission notice
are preserved on all copies.
Permission is granted to copy, distribute and/or modify this document
under the terms of the GNU Free Documentation License, Version 1.1
or any later version published by the Free Software Foundation;
with no Invariant Sections, with no
Front-Cover Texts, and with no Back-Cover Texts.
A copy of the license is included in the section entitled ``GNU
Free Documentation License''.
@ignore
Permission is granted to process this file through TeX and print the
results, provided the printed document carries copying permission
notice identical to this one except for the removal of this paragraph
(this paragraph not being relevant to the printed manual).
@end ignore
Permission is granted to copy and distribute modified versions of this
manual under the conditions for verbatim copying, provided that the entire
resulting derived work is distributed under the terms of a permission
notice identical to this one.
Permission is granted to copy and distribute translations of this manual
into another language, under the above conditions for modified versions,
except that this permission notice may be stated in a translation approved
by the Foundation.
@end ifinfo
@setchapternewpage odd
@@ -512,27 +501,21 @@ by the Foundation.
@page
@vskip 0pt plus 1filll
Copyright @copyright{} 1992, 1994, 1995, 1996, 1997, 1999 Free Software
Copyright @copyright{} 1992, 1994, 1995, 1996, 1997, 1999, 2000 Free Software
Foundation, Inc.
Permission is granted to make and distribute verbatim copies of
this manual provided the copyright notice and this permission notice
are preserved on all copies.
Permission is granted to copy and distribute modified versions of this
manual under the conditions for verbatim copying, provided that the entire
resulting derived work is distributed under the terms of a permission
notice identical to this one.
Permission is granted to copy and distribute translations of this manual
into another language, under the above conditions for modified versions,
except that this permission notice may be stated in a translation approved
by the Foundation.
Permission is granted to copy, distribute and/or modify this document
under the terms of the GNU Free Documentation License, Version 1.1
or any later version published by the Free Software Foundation;
with no Invariant Sections, with no
Front-Cover Texts, and with no Back-Cover Texts.
A copy of the license is included in the section entitled ``GNU
Free Documentation License''.
@end titlepage
@ifnottex
@node Top
@top Tar
@top @sc{gnu} tar: an archiver tool
@cindex file archival
@cindex archiving files
@@ -555,6 +538,7 @@ document. The rest of the menu lists all the lower level nodes.
* Date input formats::
* Formats::
* Media::
* GNU Free Documentation License::
* Index::
@detailmenu
@@ -736,14 +720,14 @@ Crossing Filesystem Boundaries
Date input formats
* General date syntax:: Common rules.
* Calendar date item:: 19 Dec 1994.
* Time of day item:: 9:20pm.
* Time zone item:: @sc{est}, @sc{gmt}, @sc{utc}, ...
* Day of week item:: Monday and others.
* Relative item in date strings:: next tuesday, 2 years ago.
* Pure numbers in date strings:: 19931219, 1440.
* Authors of getdate:: Bellovin, Berets, Eggert, Salz, et al.
* General date syntax:: Common rules.
* Calendar date items:: 19 Dec 1994.
* Time of day items:: 9:20pm.
* Time zone items:: @sc{est}, @sc{pdt}, @sc{gmt}, ...
* Day of week items:: Monday and others.
* Relative items in date strings:: next tuesday, 2 years ago.
* Pure numbers in date strings:: 19931219, 1440.
* Authors of getdate:: Bellovin, Eggert, Berets, Salz, et al.
Controlling the Archive Format
@@ -1436,7 +1420,7 @@ easiest to understand (and we encourage you to do the same when you use
Note that the part of the command which says,
@w{@kbd{--file=collection.tar}} is considered to be @emph{one} argument.
If you substituted any other string of characters for
@kbd{`collection.tar'}, then that string would become the name of the
@kbd{collection.tar}, then that string would become the name of the
archive file you create.
The order of the options becomes more important when you begin to use
@@ -2131,6 +2115,14 @@ You will likely use some options frequently, while you will only use
others infrequently, or not at all. (A full list of options is
available in @pxref{All Options}.)
The @env{TAR_OPTIONS} environment variable specifies default options to
be placed in front of any explicit options. For example, if
@code{TAR_OPTIONS} is @samp{-v --unlink-first}, @command{tar} behaves as
if the two options @option{-v} and @option{--unlink-first} had been
specified before any explicit options. Option specifications are
separated by whitespace. A backslash escapes the next character, so it
can be used to specify an option containing whitespace or a backslash.
Note that @command{tar} options are case sensitive. For example, the
options @samp{-T} and @samp{-t} are different; the first requires an
argument for stating the name of a file providing a list of @var{name}s,
@@ -2511,9 +2503,14 @@ member names. This option disables that behavior. @FIXME-xref{}
@item --atime-preserve
Tells @command{tar} to preserve the access time field in a file's inode when
dumping it. Due to limitations in the @code{utimes} system call, the
reading it. Due to limitations in the @code{utimes} system call, the
modification time field is also preserved, which may cause problems if
the file is simultaneously being modified by another program. @FIXME-xref{}
the file is simultaneously being modified by another program.
This option is incompatible with incremental backups, because
preserving the access time involves updating the last-changed time.
Also, this option does not work on files that you do not own,
unless you're root.
@FIXME-xref{}
@item --backup=@var{backup-type}
@@ -2534,7 +2531,7 @@ Sets the blocking factor @command{tar} uses to @var{blocking} x 512 bytes per
record. @FIXME-xref{}
@item --bzip2
@itemx -I
@itemx -j
This option tells @command{tar} to read or write archives through @code{bzip2}.
@FIXME-xref{}
@@ -2590,6 +2587,7 @@ performs operations on, rather than @command{tar}'s compilation dependent
default. @FIXME-xref{}
@item --files-from=@var{file}
@itemx -I @var{file}
@itemx -T @var{file}
@command{tar} will use the contents of @var{file} as a list of archive members
@@ -2766,7 +2764,7 @@ directory. @FIXME-xref{}
@item --overwrite
Overwrite existing files and directory metadata when extracting files
from an archive. @xref{Writing}.
from an archive. @xref{Overwrite Old Files}.
@item --owner=@var{user}
@@ -2981,7 +2979,7 @@ them with the equivalent long option.
@item -I
@samp{--bzip2}
@samp{--files-from}
@item -K
@@ -3405,8 +3403,8 @@ A socket is stored, within a @sc{gnu} @command{tar} archive, as a pipe.
@item @value{op-list}
@sc{gnu} @command{tar} now shows dates as @samp{1996-11-09}, while it used to
show them as @samp{Nov 11 1996}. (One can revert to the old behavior by
@sc{gnu} @command{tar} now shows dates as @samp{1996-08-30}, while it used to
show them as @samp{Aug 30 1996}. (One can revert to the old behavior by
defining @code{USE_OLD_CTIME} in @file{src/list.c} before reinstalling.)
But preferably, people should get used to ISO 8601 dates. Local
American dates should be made available again with full date localization
@@ -4117,7 +4115,8 @@ encountered while reading an archive. Use in conjunction with
When extracting files, if @command{tar} discovers that the extracted
file already exists, it normally replaces the file by removing it before
extracting it, to prevent confusion in the presence of hard or symbolic
links. However, if a directory cannot be removed because it is
links. (If the existing file is a symbolic link, it is removed, not
followed.) However, if a directory cannot be removed because it is
nonempty, @command{tar} neither removes it nor modifies its ownership,
permissions, or time stamps.
@@ -4127,7 +4126,39 @@ to replace or update a file that already exists, i.e., a file with the
same name as an archive member prevents extraction of that archive
member.
To overwrite existing files, use the @value{op-overwrite} option. This
To be more aggressive about altering existing files, use the
@value{op-overwrite} option. It causes @command{tar} to overwrite
existing files and to follow existing symbolic links when extracting.
Some people argue that @sc{gnu} @command{tar} should not hesitate to overwrite
files with other files when extracting. When extracting a @command{tar}
archive, they expect to see a faithful copy of the state of the filesystem
when the archive was created. It is debatable that this would always
be a proper behavior. For example, suppose one has an archive in
which @file{usr/local} is a link to @file{usr/local2}. Since then,
maybe the site removed the link and renamed the whole hierarchy from
@file{/usr/local2} to @file{/usr/local}. Such things happen all the time.
I guess it would not be welcome at all that @sc{gnu} @command{tar} removes the
whole hierarchy just to make room for the link to be reinstated (unless it
@emph{also} simultaneously restores the full @file{/usr/local2}, of course!
@sc{gnu} @command{tar} is indeed able to remove a whole hierarchy to reestablish a
symbolic link, for example, but @emph{only if} @value{op-recursive-unlink}
is specified to allow this behavior. In any case, single files are
silently removed.
Finally, the @value{op-unlink-first} option can improve performance in
some cases by causing @command{tar} to remove files unconditionally
before extracting them.
@node Overwrite Old Files
@unnumberedsubsubsec Overwrite Old Files
@table @kbd
@item --overwrite
Overwrite existing files and directory metadata when extracting files
from an archive.
This
causes @command{tar} to write extracted files into the file system without
regard to the files already on the system; i.e., files with the same
names as archive members are overwritten when the archive is extracted.
@@ -4144,32 +4175,6 @@ combined with the @value{op-absolute-names} option, as this combination
can change the contents, ownership or permissions of any file on your
system. Also, many systems do not take kindly to overwriting files that
are currently being executed.
@FIXME{these two P's have problems. i don't understand what they're
trying to talk about well enough to fix them; i may have just made them
worse (in particular the first of the two). waiting to talk with hag.}
The @value{op-unlink-first} option causes @command{tar} to always
attempt to remove a file unconditionally before attempting to extract
it. This can make @command{tar} run a bit faster if you know in advance
that the extracted files all need to be removed. Normally this option
slows @command{tar} tar down slightly, so it is disabled by default.
@FIXME{huh?} If you specify the @value{op-recursive-unlink} option,
@command{tar} removes @emph{anything} that keeps you from extracting a file
as far as current permissions will allow it. This could include removal
of the contents of a full directory hierarchy. For example, someone
using this feature may be very surprised at the results when extracting
a directory entry from the archive. This option can be dangerous; be
very aware of what you are doing if you choose to use it.
@node Overwrite Old Files
@unnumberedsubsubsec Overwrite Old Files
@table @kbd
@item --overwrite
Overwrite existing files and directory metadata when extracting files
from an archive.
@end table
@node Keep Old Files
@@ -4193,6 +4198,9 @@ extraction.
@item --unlink-first
@itemx -U
Remove files before extracting over them.
This can make @command{tar} run a bit faster if you know in advance
that the extracted files all need to be removed. Normally this option
slows @command{tar} down slightly, so it is disabled by default.
@end table
@node Recursive Unlink
@@ -4204,21 +4212,10 @@ When this option is specified, try removing files and directory hierarchies
before extracting over them. @emph{This is a dangerous option!}
@end table
Some people argue that @sc{gnu} @command{tar} should not hesitate to overwrite
files with other files when extracting. When extracting a @command{tar}
archive, they expect to see a faithful copy of the state of the filesystem
when the archive was created. It is debatable that this would always
be a proper behavior. For example, suppose one has an archive in
which @file{usr/local} is a link to @file{usr/local2}. Since then,
maybe the site removed the link and renamed the whole hierarchy from
@file{/usr/local2} to @file{/usr/local}. Such things happen all the time.
I guess it would not be welcome at all that @sc{gnu} @command{tar} removes the
whole hierarchy just to make room for the link to be reinstated (unless it
@emph{also} simultaneously restores the full @file{/usr/local2}, of course!
@sc{gnu} @command{tar} is indeed able to remove a whole hierarchy to reestablish a
symbolic link, for example, but @emph{only if} @value{op-recursive-unlink}
is specified to allow this behavior. In any case, single files are
silently removed.
If you specify the @value{op-recursive-unlink} option,
@command{tar} removes @emph{anything} that keeps you from extracting a file
as far as current permissions will allow it. This could include removal
of the contents of a full directory hierarchy.
@node Modification Times
@unnumberedsubsubsec Setting Modification Times
@@ -4449,7 +4446,7 @@ set, the default is @samp{~}, just as in Emacs.
@end table
Some people express the desire to @emph{always} use the @var{op-backup}
Some people express the desire to @emph{always} use the @value{op-backup}
option, by defining some kind of alias or script. This is not as easy
as one may think, due to the fact that old style options should appear first
and consume arguments a bit unpredictably for an alias or script. But,
@@ -4815,6 +4812,11 @@ and device but a changed directory name. The file is updated after
the files to be archived are determined, but before the new archive is
actually created.
Incremental dumps depend crucially on time stamps, so the results are
unreliable if you modify a file's time stamps during dumping (e.g.@:
with the @samp{--atime-preserve} option), or if you set the clock
backwards.
Despite it should be obvious that a device has a non-volatile value, NFS
devices have non-dependable values when an automounter gets in the picture.
This led to a great deal of spurious redumping in incremental dumps,
@@ -4916,7 +4918,7 @@ attached to the host on which the dump scripts are run.
@item TAPE_STATUS
The command to use to obtain the status of the archive device,
including error count. On some tape drives there may not be such a
command; in that case, simply use `TAPE_STATUS=false'.
command; in that case, simply use @samp{TAPE_STATUS=false}.
@item BLOCKING
The blocking factor @command{tar} will use when writing the dump archive.
@@ -5279,13 +5281,14 @@ the list of files to archive with the @command{find} utility.
@table @kbd
@item --files-from=@var{file name}
@itemx -I @var{file name}
@itemx -T @var{file name}
Get names to extract or create from file @var{file name}.
@end table
If you give a single dash as a file name for @samp{--files-from}, (i.e.,
you specify either @samp{--files-from=-} or @samp{-T -}), then the file
names are read from standard input.
you specify either @samp{--files-from=-} or @samp{-I -}) or @samp{-T
-}), then the file names are read from standard input.
Unless you are running @command{tar} with @samp{--create}, you can not use
both @samp{--files-from=-} and @samp{--file=-} (@samp{-f -}) in the same
@@ -5878,382 +5881,7 @@ $ @kbd{(cd / && tar -c -f archive.tar home)}
$ @kbd{tar -c -f archive.tar -C / home}
@end example
@node Date input formats
@chapter Date input formats
@cindex date input formats
@findex getdate
@quotation
Our units of temporal measurement, from seconds on up to months, are so
complicated, asymmetrical and disjunctive so as to make coherent mental
reckoning in time all but impossible. Indeed, had some tyrannical god
contrived to enslave our minds to time, to make it all but impossible
for us to escape subjection to sodden routines and unpleasant surprises,
he could hardly have done better than handing down our present system.
It is like a set of trapezoidal building blocks, with no vertical or
horizontal surfaces, like a language in which the simplest thought
demands ornate constructions, useless particles and lengthy
circumlocutions. Unlike the more successful patterns of language and
science, which enable us to face experience boldly or at least
level-headedly, our system of temporal calculation silently and
persistently encourages our terror of time.
@dots{} It is as though architects had to measure length in feet, width
in meters and height in ells; as though basic instruction manuals
demanded a knowledge of five different languages. It is no wonder then
that we often look into our own immediate past or future, last Tuesday
or a week from Sunday, with feelings of helpless confusion. @dots{}
--- Robert Grudin, @cite{Time and the Art of Living}.
@end quotation
This section describes the textual date representations that @sc{gnu}
programs accept. These are the strings you, as a user, can supply as
arguments to the various programs. The C interface (via the
@code{getdate} function) is not described here.
@cindex beginning of time, for Unix
@cindex epoch, for Unix
Although the date syntax here can represent any possible time since zero
A.D., computer integers are not big enough for such a (comparatively)
long time. The earliest date semantically allowed on Unix systems is
midnight, 1 January 1970 UCT.
@menu
* General date syntax:: Common rules.
* Calendar date item:: 19 Dec 1994.
* Time of day item:: 9:20pm.
* Time zone item:: @sc{est}, @sc{gmt}, @sc{utc}, ...
* Day of week item:: Monday and others.
* Relative item in date strings:: next tuesday, 2 years ago.
* Pure numbers in date strings:: 19931219, 1440.
* Authors of getdate:: Bellovin, Berets, Eggert, Salz, et al.
@end menu
@node General date syntax
@section General date syntax
@cindex general date syntax
@cindex items in date strings
A @dfn{date} is a string, possibly empty, containing many items
separated by white space. The white space may be omitted when no
ambiguity arises. The empty string means the beginning of today (i.e.,
midnight). Order of the items is immaterial. A date string may contain
many flavors of items:
@itemize @bullet
@item calendar date items
@item time of the day items
@item time zone items
@item day of the week items
@item relative items
@item pure numbers.
@end itemize
@noindent We describe each of these item types in turn, below.
@cindex numbers, written-out
@cindex ordinal numbers
@findex first @r{in date strings}
@findex next @r{in date strings}
@findex last @r{in date strings}
A few numbers may be written out in words in most contexts. This is
most useful for specifying day of the week items or relative items (see
below). Here is the list: @samp{first} for 1, @samp{next} for 2,
@samp{third} for 3, @samp{fourth} for 4, @samp{fifth} for 5,
@samp{sixth} for 6, @samp{seventh} for 7, @samp{eighth} for 8,
@samp{ninth} for 9, @samp{tenth} for 10, @samp{eleventh} for 11 and
@samp{twelfth} for 12. Also, @samp{last} means exactly @math{-1}.
@cindex months, written-out
When a month is written this way, it is still considered to be written
numerically, instead of being ``spelled in full''; this changes the
allowed strings.
@cindex case, ignored in dates
@cindex comments, in dates
Alphabetic case is completely ignored in dates. Comments may be introduced
between round parentheses, as long as included parentheses are properly
nested. Hyphens not followed by a digit are currently ignored. Leading
zeros on numbers are ignored.
@node Calendar date item
@section Calendar date item
@cindex calendar date item
A @dfn{calendar date item} specifies a day of the year. It is
specified differently, depending on whether the month is specified
numerically or literally. All these strings specify the same calendar date:
@example
1970-09-17 # ISO 8601.
70-9-17 # This century assumed by default.
70-09-17 # Leading zeros are ignored.
9/17/72 # Common U.S. writing.
24 September 1972
24 Sept 72 # September has a special abbreviation.
24 Sep 72 # Three-letter abbreviations always allowed.
Sep 24, 1972
24-sep-72
24sep72
@end example
The year can also be omitted. In this case, the last specified year is
used, or the current year if none. For example:
@example
9/17
sep 17
@end example
Here are the rules.
@cindex ISO 8601 date format
@cindex date format, ISO 8601
For numeric months, the ISO 8601 format
@samp{@var{year}-@var{month}-@var{day}} is allowed, where @var{year} is
any positive number, @var{month} is a number between 01 and 12, and
@var{day} is a number between 01 and 31. A leading zero must be present
if a number is less than ten. If @var{year} is less than 100, then 1900
is added to it to force a date in this century. The construct
@samp{@var{month}/@var{day}/@var{year}}, popular in the United States,
is accepted. Also @samp{@var{month}/@var{day}}, omitting the year.
@cindex month names in date strings
@cindex abbreviations for months
Literal months may be spelled out in full: @samp{January},
@samp{February}, @samp{March}, @samp{April}, @samp{May}, @samp{June},
@samp{July}, @samp{August}, @samp{September}, @samp{October},
@samp{November} or @samp{December}. Literal months may be abbreviated
to their first three letters, possibly followed by an abbreviating dot.
It is also permitted to write @samp{Sept} instead of @samp{September}.
When months are written literally, the calendar date may be given as any
of the following:
@example
@var{day} @var{month} @var{year}
@var{day} @var{month}
@var{month} @var{day} @var{year}
@var{day}-@var{month}-@var{year}
@end example
Or, omitting the year:
@example
@var{month} @var{day}
@end example
@node Time of day item
@section Time of day item
@cindex time of day item
A @dfn{time of day item} in date strings specifies the time on a given
day. Here are some examples, all of which represent the same time:
@example
20:02:0
20:02
8:02pm
20:02-0500 # In @sc{est} (U.S. Eastern Standard Time).
@end example
More generally, the time of the day may be given as
@samp{@var{hour}:@var{minute}:@var{second}}, where @var{hour} is
a number between 0 and 23, @var{minute} is a number between 0 and
59, and @var{second} is a number between 0 and 59. Alternatively,
@samp{:@var{second}} can be omitted, in which case it is taken to
be zero.
@findex am @r{in date strings}
@findex pm @r{in date strings}
@findex midnight @r{in date strings}
@findex noon @r{in date strings}
If the time is followed by @samp{am} or @samp{pm} (or @samp{a.m.}
or @samp{p.m.}), @var{hour} is restricted to run from 1 to 12, and
@samp{:@var{minute}} may be omitted (taken to be zero). @samp{am}
indicates the first half of the day, @samp{pm} indicates the second
half of the day. In this notation, 12 is the predecessor of 1:
midnight is @samp{12am} while noon is @samp{12pm}.
(This is the zero-oriented interpretation of @samp{12am} and @samp{12pm},
as opposed to the old tradition derived from Latin
which uses @samp{12m} for noon and @samp{12pm} for midnight.)
@cindex time zone correction
@cindex minutes, time zone correction by
The time may be followed by a time zone correction,
expressed as @samp{@var{s}@var{hh}@var{mm}}, where @var{s} is @samp{+}
or @samp{-}, @var{hh} is a number of zone hours and @var{mm} is a number
of zone minutes. When a time zone correction is given this way, it
forces interpretation of the time in @sc{utc}, overriding any previous
specification for the time zone or the local time zone. The @var{minute}
part of the time of the day may not be elided when a time zone correction
is used.
Either @samp{am}/@samp{pm} or a time zone correction may be specified,
but not both.
@node Time zone item
@section Time zone item
@cindex time zone item
A @dfn{time zone item} specifies an international time zone, indicated
by a small set of letters, e.g.@: @samp{UTC} for Coordinated Universal
Time. Any included period is ignored. By following a
non-daylight-saving time zone by the string @samp{DST} in a separate
word (that is, separated by some white space), the corresponding
daylight saving time zone may be specified.
Time zone items are obsolescent and are not recommended, because they
are ambiguous; for example, @samp{EST} has a different meaning in
Australia than in the United States. Instead, it's better to use
unambiguous numeric time zone corrections like @samp{-0500}, as
described in the previous section.
@node Day of week item
@section Day of week item
@cindex day of week item
The explicit mention of a day of the week will forward the date
(only if necessary) to reach that day of the week in the future.
Days of the week may be spelled out in full: @samp{Sunday},
@samp{Monday}, @samp{Tuesday}, @samp{Wednesday}, @samp{Thursday},
@samp{Friday} or @samp{Saturday}. Days may be abbreviated to their
first three letters, optionally followed by a period. The special
abbreviations @samp{Tues} for @samp{Tuesday}, @samp{Wednes} for
@samp{Wednesday} and @samp{Thur} or @samp{Thurs} for @samp{Thursday} are
also allowed.
@findex next @var{day}
@findex last @var{day}
A number may precede a day of the week item to move forward
supplementary weeks. It is best used in expression like @samp{third
monday}. In this context, @samp{last @var{day}} or @samp{next
@var{day}} is also acceptable; they move one week before or after
the day that @var{day} by itself would represent.
A comma following a day of the week item is ignored.
@node Relative item in date strings
@section Relative item in date strings
@cindex relative items in date strings
@cindex displacement of dates
@dfn{Relative items} adjust a date (or the current date if none) forward
or backward. The effects of relative items accumulate. Here are some
examples:
@example
1 year
1 year ago
3 years
2 days
@end example
@findex year @r{in date strings}
@findex month @r{in date strings}
@findex fortnight @r{in date strings}
@findex week @r{in date strings}
@findex day @r{in date strings}
@findex hour @r{in date strings}
@findex minute @r{in date strings}
The unit of time displacement may be selected by the string @samp{year}
or @samp{month} for moving by whole years or months. These are fuzzy
units, as years and months are not all of equal duration. More precise
units are @samp{fortnight} which is worth 14 days, @samp{week} worth 7
days, @samp{day} worth 24 hours, @samp{hour} worth 60 minutes,
@samp{minute} or @samp{min} worth 60 seconds, and @samp{second} or
@samp{sec} worth one second. An @samp{s} suffix on these units is
accepted and ignored.
@findex ago @r{in date strings}
The unit of time may be preceded by a multiplier, given as an optionally
signed number. Unsigned numbers are taken as positively signed. No
number at all implies 1 for a multiplier. Following a relative item by
the string @samp{ago} is equivalent to preceding the unit by a
multiplier with value @math{-1}.
@findex day @r{in date strings}
@findex tomorrow @r{in date strings}
@findex yesterday @r{in date strings}
The string @samp{tomorrow} is worth one day in the future (equivalent
to @samp{day}), the string @samp{yesterday} is worth
one day in the past (equivalent to @samp{day ago}).
@findex now @r{in date strings}
@findex today @r{in date strings}
@findex this @r{in date strings}
The strings @samp{now} or @samp{today} are relative items corresponding
to zero-valued time displacement, these strings come from the fact
a zero-valued time displacement represents the current time when not
otherwise change by previous items. They may be used to stress other
items, like in @samp{12:00 today}. The string @samp{this} also has
the meaning of a zero-valued time displacement, but is preferred in
date strings like @samp{this thursday}.
@node Pure numbers in date strings
@section Pure numbers in date strings
@cindex pure numbers in date strings
The precise interpretation of a pure decimal number depends on
the context in the date string.
If the decimal number is of the form @var{yyyy}@var{mm}@var{dd} and no
other calendar date item (@pxref{Calendar date item}) appears before it
in the date string, then @var{yyyy} is read as the year, @var{mm} as the
month number and @var{dd} as the day of the month, for the specified
calendar date.
If the decimal number is of the form @var{hh}@var{mm} and no other time
of day item appears before it in the date string, then @var{hh} is read
as the hour of the day and @var{mm} as the minute of the hour, for the
specified time of the day. @var{mm} can also be omitted.
If both a calendar date and a time of day appear to the left of a number
in the date string, but no relative item, then the number overrides the
year.
@node Authors of getdate
@section Authors of @code{getdate}
@cindex authors of @code{getdate}
@cindex Bellovin, Steven M.
@cindex Berets, Jim
@cindex Eggert, Paul
@cindex MacKenzie, David
@cindex Meyering, Jim
@cindex Salz, Rich
@code{getdate} was originally implemented by Steven M. Bellovin
(@samp{smb@@research.att.com}) while at the University of North Carolina
at Chapel Hill. The code was later tweaked by a couple of people on
Usenet, then completely overhauled by Rich $alz (@samp{rsalz@@bbn.com})
and Jim Berets (@samp{jberets@@bbn.com}) in August, 1990. Various
revisions for the @sc{gnu} system were made by David MacKenzie, Jim Meyering,
and others. The code was rewritten again in August, 1999 by Paul Eggert,
to improve its support for daylight saving time.
@cindex Pinard, F.
@cindex Berry, K.
This chapter was originally produced by Fran@,{c}ois Pinard
(@samp{pinard@@iro.umontreal.ca}) from the @file{getdate.y} source code,
and then edited by K.@: Berry (@samp{kb@@cs.umb.edu}).
@include getdate.texi
@node Formats
@chapter Controlling the Archive Format
@@ -6438,7 +6066,7 @@ the @sc{posix} format that we still cannot support. This simple question
has a complex answer. Maybe that, on intimate look, some strong
limitations will pop up, but until now, nothing sounds too difficult
(but see below). I only have these few pages of @sc{posix} telling about
`Extended tar Format' (P1003.1-1990 -- section 10.1.1), and there are
``Extended tar Format'' (P1003.1-1990 -- section 10.1.1), and there are
references to other parts of the standard I do not have, which should
normally enforce limitations on stored file names (I suspect things
like fixing what @kbd{/} and @kbd{@key{NUL}} means). There are also
@@ -6707,7 +6335,7 @@ lose some compressibility. But this would have make recovering easier.
So, there are pros and cons. We'll see!
@table @kbd
@item -I
@item -j
@itemx --bzip2
Filter the archive through @code{bzip2}. Otherwise like @value{op-gzip}.
@@ -6735,8 +6363,8 @@ utility from within @command{tar} because the @command{compress} utility by
itself cannot access remote tape drives.
The @value{op-compress} option will not work in conjunction with the
@value{op-multi-volume} option or the @value{op-append}, @value{op-update},
@value{op-append} and @value{op-delete} operations. @xref{Operations}, for
@value{op-multi-volume} option or the @value{op-append}, @value{op-update}
and @value{op-delete} operations. @xref{Operations}, for
more information on these operations.
If there is no compress utility available, @command{tar} will report an error.
@@ -6921,19 +6549,18 @@ get it right.
When @command{tar} reads files, this causes them to have the access
times updated. To have @command{tar} attempt to set the access times
back to what they were before they were read, use the
@value{op-atime-preserve} option. This doesn't work for files that you
don't own, unless you're root, and it doesn't interact with incremental
dumps nicely (@pxref{Backups}), and it can set access or modification
times incorrectly if other programs access the file while @command{tar}
is running; but it is good enough for some purposes.
@value{op-atime-preserve} option.
Handling of file attributes
@table @kbd
@item --atime-preserve
Preserve access times on dumped files. This also preserves modification
times, which can be unfortunate if other programs are simultaneously
modifying the dumped files.
Preserve access times on files that are read.
This doesn't work for files that
you don't own, unless you're root, and it doesn't interact with
incremental dumps nicely (@pxref{Backups}), and it can set access or
modification times incorrectly if other programs access the file while
@command{tar} is running; but it is good enough for some purposes.
@item -m
@itemx --touch
@@ -8651,9 +8278,7 @@ To check for discrepancies in an archive immediately after it is
written, use the @value{op-verify} option in conjunction with
the @value{op-create} operation. When this option is
specified, @command{tar} checks archive members against their counterparts
in the file system, and reports discrepancies on the standard error. In
multi-volume archives, each volume is verified after it is written,
before the next volume is written.
in the file system, and reports discrepancies on the standard error.
To verify an archive, you must be able to read it from before the end
of the last written entry. This option is useful for detecting data
@@ -8683,6 +8308,11 @@ magnetic heads, some able to read after the writes occurred. One would
not say that drivers unable to detect all cases are necessarily flawed,
as long as programming is concerned.
The @value{op-verify} option will not work in conjunction with the
@value{op-multi-volume} option or the @value{op-append},
@value{op-update} and @value{op-delete} operations. @xref{Operations},
for more information on these operations.
@node Write Protection
@section Write Protection
@@ -8699,6 +8329,8 @@ disabled) switch, a notch which can be popped out or covered, a ring
which can be removed from the center of a tape reel, or some other
changeable feature.
@include fdl.texi
@node Index
@unnumbered Index