ESXi ash/dash/busybox shell getting current timestamp in UTC ISO8601 format without colons or dashes
Posted by jpluimers on 2022/01/17
On VMware ESXi, with the Busybox ash/dash shell, I wanted to get the current UTC timestamp in ISO 8601 format without dashes (-) or especially colons (:) and plus-signs (+) you have to back-slash escape colons or double quote parameters, which is often can be a pain).
- [Wayback] How to Manipulate Filenames Having Spaces and Special Characters in Linux describes the pain handling special characters:
In this article, we will see how to create, copy, move and delete filenames that starts with spaces and special characters (say #, *, &, =, etc.) in Linux.
- [Wayback] filenames – What characters are safe in cross-platform file names for Linux, Windows and OS-X – Super User
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[]()^ #%&!@:+={}'~and [`] all have special meanings in many shells, and are annoying to work around, and so should be avoided. They also tend to look horrible in URLs.
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This is why we can’t have good things: Getting the UTC 8610 timestamp was far less easy than I hoped for.
First of all, Busybox only allows for a precision of seconds, not milliseconds, and the specification format needs better documentation as per [Wayback] embedded linux – How to get ISO8601 seconds format from “date” in busybox? – Stack Overflow:
The main and very subtle difference in one of my tries that I happened to miss:
# date -I 'seconds' date: invalid date 'seconds'Was off by a hair. It needed to remove the space:
# date -I'seconds' 2017-07-09T17:29:54-0400Now busybox date is happy.
This gets you an ISO 8601 timestamp that is in the local time zone (in this case UTC-4 hours used in parts of the Americas and the Caribbean), which ahead of UTC will introduce a plus sign (+) that I don’t want.
I wanted the ISO 8601 UTC time zone designation, which is Z (and in some RFCs +00:00, +0000, -00:00 or -0000).
The Busybox date command allows to specify an -u or --utc option to make a timestamp UTC as per help:
# date --help BusyBox v1.29.3 (2019-05-21 15:22:06 PDT) multi-call binary. Usage: date [OPTIONS] [+FMT] [TIME] Display time (using +FMT), or set time [-s,--set] TIME Set time to TIME -u,--utc Work in UTC (don't convert to local time) -R,--rfc-2822 Output RFC-2822 compliant date string -I[SPEC] Output ISO-8601 compliant date string SPEC='date' (default) for date only, 'hours', 'minutes', or 'seconds' for date and time to the indicated precision -r,--reference FILE Display last modification time of FILE -d,--date TIME Display TIME, not 'now' -D FMT Use FMT for -d TIME conversion Recognized TIME formats: hh:mm[:ss] [YYYY.]MM.DD-hh:mm[:ss] YYYY-MM-DD hh:mm[:ss] [[[[[YY]YY]MM]DD]hh]mm[.ss] 'date TIME' form accepts MMDDhhmm[[YY]YY][.ss] instead
Well, this is in for a surprise, as instead of Z, (or even the time zones +00:00, +0000, -00:00 or -0000), the UTC time zone designator is used: clearly not ISO 8601 compliant.
# date -I'seconds' 2021-05-09T14:23:38+0000 # date --utc -I'seconds' 2021-05-09T14:23:38UTC
Like VMware ESXi console: viewing all VMs, suspending and waking them up: part 1, sed and regular expressions come to the recue again after a try at regex101.com/r/lzeXIP
# date --utc -I'seconds' 2021-05-09T15:45:04UTC # date --utc -I'seconds' | sed -n -E -e "s/^([[:digit:]]{4})\-([[:digit:]]{2})\-([[:digit:]]{2}T[[:digit:]]{2})\:([[:digit:]]{2})\:([[:digit:]]{2})UTC$/\1\2\3\4\5Z/p" 20210509T154504Z
It relies heavily on grouping, but works pretty nicely.
–jeroen
The Wiert Corner - irregular stream of stuff 
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