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The --after-date=date (--newer=date, -N date) option causes tar to only work on files whose data modification or status change times are newer than the date given. If date starts with ‘/’ or ‘.’, it is taken to be a file name; the data modification time of that file is used as the date. 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 file's data (rather than status 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.
Acts on files only if their data modification or status change times are later than date. Use in conjunction with any operation.
If date starts with ‘/’ or ‘.’, it is taken to be a file name; the data modification time of that file is used as the date.
These options limit tar to operate only on files which have been modified after the date specified. A file's status is considered to have changed if its contents have been modified, or if its owner, permissions, and so forth, have been changed. (For more information on how to specify a date, see Date input formats; remember that the entire date argument must be quoted if it contains any spaces.)
Gurus would say that --after-date tests both the data
modification time (mtime, the time the contents of the file
were last modified) and the status change time (ctime, the time
the file's status was last changed: owner, permissions, etc.)
fields, while --newer-mtime tests only the mtime
field.
To be precise, --after-date checks both mtime and
ctime and processes the file if either one is more recent than
date, while --newer-mtime only checks mtime and
disregards ctime. Neither does it use 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. For example, the following command will add to the archive all the files modified less than two days ago:
$ tar -cf foo.tar --newer-mtime '2 days ago'
When any of these options is used with the option --verbose (see verbose tutorial) GNU tar will try to convert the specified date back to its textual representation and compare that with the one given with the option. If the two dates differ, tar will print a warning saying what date it will use. This is to help user ensure he is using the right date. For example:
$ tar -c -f archive.tar --after-date='10 days ago' .
tar: Option --after-date: Treating date `10 days ago' as 2006-06-11
13:19:37.232434
Please Note: --after-date and --newer-mtime should not be used for incremental backups. See Incremental Dumps, for proper way of creating incremental backups.