10.1.6 Formatting file timestamps

By default, file timestamps are listed in abbreviated form. Most locales use a timestamp like `2002-03-30 23:45'. However, the default POSIX locale uses a date like `Mar 30  2002' for non-recent timestamps, and a date-without-year and time like `Mar 30 23:45' for recent timestamps.

A timestamp is considered to be recent if it is less than six months old, and is not dated in the future. If a timestamp dated today is not listed in recent form, the timestamp is in the future, which means you probably have clock skew problems which may break programs like make that rely on file timestamps.

The following option changes how file timestamps are printed.

`--time-style=style'

List timestamps in style style. The style should be one of the following:

`+format'

List timestamps using format, where format is interpreted like the format argument of date (see section 21.1 date: Print or set system date and time). For example, `--time-style="+%Y-%m-%d %H:%M:S"' causes ls to list timestamps like `2002-03-30 23:45:56'. As with date, format's interpretation is affected by the LC_TIME locale category.

If format contains two format strings separated by a newline, the former is used for non-recent files and the latter for recent files; if you want output columns to line up, you may need to insert spaces in one of the two formats.

`full-iso'

List timestamps in full using ISO 8601 date, time, and time zone format with nanosecond precision, e.g., `2002-03-30 23:45:56.477817180 -0700'. This style is equivalent to `+%Y-%m-%d %H:%M:%S.%N %z'.

This is useful because the time output includes all the information that is available from the operating system. For example, this can help explain make's behavior, since GNU make uses the full timestamp to determine whether a file is out of date.

`long-iso'

List ISO 8601 date and time in minutes, e.g., `2002-03-30 23:45'. These timestamps are shorter than `full-iso' timestamps, and are usually good enough for everyday work. This style is equivalent to `%Y-%m-%d %H:%M'.

`iso'

List ISO 8601 dates for non-recent timestamps (e.g., `2002-03-30 '), and ISO 8601 month, day, hour, and minute for recent timestamps (e.g., `03-30 23:45'). These timestamps are uglier than `long-iso' timestamps, but they carry nearly the same information in a smaller space and their brevity helps ls output fit within traditional 80-column output lines. The following two ls invocations are equivalent:

newline=' ' ls -l --time-style="+%Y-%m-%d $newline%m-%d %H:%M" ls -l --time-style="iso"

`locale'

List timestamps in a locale-dependent form. For example, a Finnish locale might list non-recent timestamps like `maalis 30  2002' and recent timestamps like `maalis 30 23:45'. Locale-dependent timestamps typically consume more space than `iso' timestamps and are harder for programs to parse because locale conventions vary so widely, but they are easier for many people to read.

The LC_TIME locale category specifies the timestamp format. The default POSIX locale uses timestamps like `Mar 30  2002' and `Mar 30 23:45'; in this locale, the following two ls invocations are equivalent:

newline=' ' ls -l --time-style="+%b %e %Y$newline%b %e %H:%M" ls -l --time-style="locale"

Other locales behave differently. For example, in a German locale, `--time-style="locale"' might be equivalent to `--time-style="+%e. %b %Y $newline%e. %b %H:%M"' and might generate timestamps like `30. Mär 2002 ' and `30. Mär 23:45'.

`posix-style'

List POSIX-locale timestamps if the LC_TIME locale category is POSIX, style timestamps otherwise. For example, the default style, which is `posix-long-iso', lists timestamps like `Mar 30  2002' and `Mar 30 23:45' when in the POSIX locale, and like `2002-03-30 23:45' otherwise.

You can specify the default value of the `--time-style' option with the environment variable TIME_STYLE; if TIME_STYLE is not set the default style is `posix-long-iso'. GNU Emacs 21 and later can parse ISO dates, but older Emacs versions do not, so if you are using an older version of Emacs and specify a non-POSIX locale, you may need to set `TIME_STYLE="locale"'.