Getting The Canonical Time Zone Name in Shell Script

Getting the Canonical Time Zone name in shell script

This is more complicated than it sounds. Most linux distributions do it differently so there is no 100% reliable way to get the Olson TZ name.

Below is the heuristic that I have used in the past:

1. First check /etc/timezone, if it exists use it.
2. Next check if /etc/localtime is a symlink to the timezone database
3. Otherwise find a file in /usr/share/zoneinfo with the same content
   as the file /etc/localtime

Untested example code:

if [ -f /etc/timezone ]; then
  OLSONTZ=`cat /etc/timezone`
elif [ -h /etc/localtime ]; then
  OLSONTZ=`readlink /etc/localtime | sed "s/\/usr\/share\/zoneinfo\///"`
else
  checksum=`md5sum /etc/localtime | cut -d' ' -f1`
  OLSONTZ=`find /usr/share/zoneinfo/ -type f -exec md5sum {} \; | grep "^$checksum" | sed "s/.*\/usr\/share\/zoneinfo\///" | head -n 1`
fi

echo $OLSONTZ

Note that this quick example does not handle the case where multiple TZ names match the given file (when looking in /usr/share/zoneinfo). Disambiguating the appropriate TZ name will depend on your application.

-nick

how to get local date/time in linux terminal while server configured in UTC/different timezone?

Use the TZ environment variable to pass the desired timezone to date:

TZ=<timezone> date

You can find the available timezones in the /usr/share/zoneinfo/ directory and subdirectories. For example, /usr/share/zoneinfo/America/New_York defines TZ=America/New_York.

Example:

$ date                         
Fri Jul 29 06:31:53 BDT 2016

$ TZ='America/New_York' date   
Thu Jul 28 20:31:58 EDT 2016

$ TZ='America/Los_Angeles' date
Thu Jul 28 17:31:54 PDT 2016

How to obtain the absolute path of a file via Shell (BASH/ZSH/SH)?

Use realpath

$ realpath example.txt
/home/username/example.txt

Reliable way for a Bash script to get the full path to itself

Here's what I've come up with (edit: plus some tweaks provided by sfstewman, levigroker, Kyle Strand, and Rob Kennedy), that seems to mostly fit my "better" criteria:

SCRIPTPATH="$( cd -- "$(dirname "$0")" >/dev/null 2>&1 ; pwd -P )"

That SCRIPTPATH line seems particularly roundabout, but we need it rather than SCRIPTPATH=`pwd` in order to properly handle spaces and symlinks.

The inclusion of output redirection (>/dev/null 2>&1) handles the rare(?) case where cd might produce output that would interfere with the surrounding $( ... ) capture. (Such as cd being overridden to also ls a directory after switching to it.)

Note also that esoteric situations, such as executing a script that isn't coming from a file in an accessible file system at all (which is perfectly possible), is not catered to there (or in any of the other answers I've seen).

The -- after cd and before "$0" are in case the directory starts with a -.

How do I know the script file name in a Bash script?

me=`basename "$0"`

For reading through a symlink¹, which is usually not what you want (you usually don't want to confuse the user this way), try:

me="$(basename "$(test -L "$0" && readlink "$0" || echo "$0")")"

IMO, that'll produce confusing output. "I ran foo.sh, but it's saying I'm running bar.sh!? Must be a bug!" Besides, one of the purposes of having differently-named symlinks is to provide different functionality based on the name it's called as (think gzip and gunzip on some platforms).

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¹ That is, to resolve symlinks such that when the user executes foo.sh which is actually a symlink to bar.sh, you wish to use the resolved name bar.sh rather than foo.sh.

How can I get a human-readable timezone name in Python?

This may not have been around when this question was originally written, but here is a snippet to get the time zone official designation:

>>> eastern = timezone('US/Eastern')
>>> eastern.zone
'US/Eastern'

Further, this can be used with a non-naive datetime object (aka a datetime where the actual timezone has been set using pytz.<timezone>.localize(<datetime_object>) or datetime_object.astimezone(pytz.<timezone>) as follows:

>>> import datetime, pytz
>>> todaynow = datetime.datetime.now(tz=pytz.timezone('US/Hawaii'))
>>> todaynow.tzinfo # turned into a string, it can be split/parsed
<DstTzInfo 'US/Hawaii' HST-1 day, 14:00:00 STD>
>>> todaynow.strftime("%Z")
'HST'
>>> todaynow.tzinfo.zone
'US/Hawaii'

This is, of course, for the edification of those search engine users who landed here. ... See more at the pytz module site.

Get a list of valid time zones in Go

To get a list of time zones, you can use something like:

package main

import (
    "fmt"
    "io/ioutil"
    "strings"
)

var zoneDirs = []string{
    // Update path according to your OS
    "/usr/share/zoneinfo/",
    "/usr/share/lib/zoneinfo/",
    "/usr/lib/locale/TZ/",
}

var zoneDir string

func main() {
    for _, zoneDir = range zoneDirs {
        ReadFile("")
    }
}

func ReadFile(path string) {
    files, _ := ioutil.ReadDir(zoneDir + path)
    for _, f := range files {
        if f.Name() != strings.ToUpper(f.Name()[:1]) + f.Name()[1:] {
            continue
        }
        if f.IsDir() {
            ReadFile(path + "/" + f.Name())
        } else {
            fmt.Println((path + "/" + f.Name())[1:])
        }
    }
}

output:

Africa/Abidjan
Africa/Accra
Africa/Addis_Ababa
Africa/Algiers
Africa/Asmara
Africa/Asmera
Africa/Bamako
Africa/Bangui
...

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