The --after-date=date (--newer=date, -N date) option causes tar to only work on files
whose modification or inode-changed times are newer than the date
given. If you use this option when creating or appending to an archive,
the archive will only include new files. If you use `--after-date'
when extracting an archive, tar will only extract files newer
than the date you specify.
If you only want tar to make the date comparison based on
modification of the actual contents of the file (rather than inode
changes), then use the --newer-mtime=date option.
You may use these options with any operation. Note that these options
differ from the --update (-u) operation in that they allow you to
specify a particular date against which tar can compare when
deciding whether or not to archive the files.
These options limit tar to only operating on files which have
been modified after the date specified. A file is considered to have
changed if the contents have been modified, or if the owner,
permissions, and so forth, have been changed. (For more information on
how to specify a date, see section Date input formats; remember that the
entire date argument must be quoted if it contains any spaces.)
Gurus would say that --after-date=date (--newer=date, -N date) tests both the mtime
(time the contents of the file were last modified) and ctime
(time the file's status was last changed: owner, permissions, etc)
fields, while --newer-mtime=date tests only mtime field.
To be precise, --after-date=date (--newer=date, -N date) checks both mtime and
ctime and processes the file if either one is more recent than
date, while --newer-mtime=date only checks mtime and
disregards ctime. Neither uses atime (the last time the
contents of the file were looked at).
Date specifiers can have embedded spaces. Because of this, you may need to quote date arguments to keep the shell from parsing them as separate arguments.
@FIXME{Need example of --newer-mtime with quoted argument.}
Please Note: --after-date=date (--newer=date, -N date) and --newer-mtime=date should not be used for incremental backups. Some files (such as those in renamed directories) are not selected properly by these options. See section The Incremental Options.
To select files newer than the modification time of a file that already
exists, you can use the `--reference' (`-r') option of GNU
date, available in GNU shell utilities 1.13 or later. It returns
the timestamp of that already existing file; this timestamp expands to
become the referent date which `--newer' uses to determine which
files to archive. For example, you could say,
$ tar -cf archive.tar --newer="`date -r file`" /home
which tells @FIXME{need to fill this in!}.
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