如何使用 linux date 命令解析 ISO8601 日期

Question

I'm trying to use the date command to generate a file timestamp that the date command itself can interpret. However, the date command does not seem to like its own output, and I am not sure how to work around this. Case in point:

sh-4.2$ date
Fri Jan  3 14:22:19 PST 2014
sh-4.2$ date +%Y%m%dT%H%M
20140103T1422
sh-4.2$ date -d "20140103T1422"
Thu Jan  2 23:22:00 PST 2014

date appears to be interpreting the string with an offset of 15 hours. Are there any known workarounds for this?

Edit: this is not an issue of display:

sh-4.2$ date +%s
1388791096
sh-4.2$ date +%Y%m%dT%H%M
20140103T1518
sh-4.2$ date -d 20140103T1518 +%s
1388737080
sh-4.2$ python
Python 3.3.3 (default, Nov 26 2013, 13:33:18) 
[GCC 4.8.2] on linux
Type "help", "copyright", "credits" or "license" for more information.
>>> 1388737080 - 1388791096
-54016
>>> 54016/3600
15.004444444444445
>>> 

It's still off by 15 hours when displayed as a unix timestamp.

EDIT #1

Maybe I should pose this question a little differently. Say I have a list of ISO8601 basic timestamps of the form:

• YYYYMMDDThhmm
• YYYYMMDDThhmmss

What is the simplest way to convert them to the corresponding Unix timestamps?

For example:

- 20140103T1422   = 1388787720
- 20140103T142233 = 1388787753

Answer 1

The coreutils info docs says that ISO 8601 "extended format" is supported.

You'll need to add hyphens, colons, and a +%z to make it work.

$ date +"%Y-%m-%dT%H:%M:%S%z"
2014-01-03T16:08:23-0800
$ date -d 2014-01-03T16:08:23-0800
Fri Jan  3 16:08:23 PST 2014

To answer your second part of the question...

Since the date format only contains numbers and symbols, you could replace each symbol with a unique letter, e.g. using tr

$ ts="$(date +"%Y-%m-%dT%H:%M:%S%z" | tr -- '-:+' 'hcp')"; echo "$ts"
2014h01h03T16c18c04h0800
$ date -d "$(echo "$ts" | tr -- 'hcp' '-:+')"
Fri Jan  3 16:18:04 PST 2014

Or you could parse it using the T and the - or + as separators, e.g. using shell ${var%word} and ${var#word} expansion

$ ts="$(date +"%Y%m%dT%H%M%S%z")"; echo "$ts"
20140103T162228-0800
$ date=${ts%T*}; time=${ts#*T}
etc.    

or using bash regular expression matching

$ ts="$(date +"%Y%m%dT%H%M%S%z")"; echo "$ts"
20140103T165611-0800
$ [[ "$ts" =~ (.*)(..)(..)T(..)(..)(..)(.....) ]]
$ match=("${BASH_REMATCH[@]}")
$ Y=${match[1]}; m=${match[2]}; d=${match[3]}; H=${match[4]}; M=${match[5]}; S=${match[6]}; z=${match[7]}
$ date -d "$Y-$m-$d"T"$H:$M:$S$z"
Fri Jan  3 16:56:11 PST 2014

or Perl, Python, etc. etc.

Answer 2

You ask for "known workarounds." Here is a simple one:

$ date -d "$(echo 20140103T1422 | sed 's/T/ /')"
Fri Jan  3 14:22:00 PST 2014

This uses sed to replace "T" with a space. The result is a format that date understands.

If we add seconds onto the ISO8601 date, then date requires more changes:

$ date -d "$(echo 20140103T142211 | sed -r 's/(.*)T(..)(..)(..)/\1 \2:\3:\4/')"
Fri Jan  3 14:22:11 PST 2014

In the above, sed replaces the "T" with a space and also separates HHMMSS into HH:MM:SS.

Answer 3

GNU coreutils have only supported ISO 8601 dates as input since version 8.13 (released on 2011-09-08). You must be using an older version.

Under older versions, you need to replace the T by a space. Otherwise it is interpreted as a US military time zone.

Even under recent versions, only the fully punctuated form is recognized, not the basic format with only digits and a T in the middle.

# Given a possibly abbreviated ISO date $iso_date...
date_part=${iso_date%%T*}
if [ "$date_part" != "$iso_date" ]; then
  time_part=${abbreviated_iso_date#*T}
  case ${iso_date#*T} in
    [!0-9]*) :;;
    [0-9]|[0-9][0-9]) time_part=${time_part}:00;;
    *)
      hour=${time_part%${time_part#??}}
      minute=${time_part%${time_part#????}}; minute=${minute#??}
      time_part=${hour}:${minute}:${time_part#????};;
  esac
else
  time_part=
fi
date -d "$date_part $time_part"