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#!/usr/bin/bash

PKGVERSION="(GNU libc) "
TZVERSION="2.28"
REPORT_BUGS_TO="<http://www.gnu.org/software/libc/bugs.html>"

# Ask the user about the time zone, and output the resulting TZ value to stdout.
# Interact with the user via stderr and stdin.

# Contributed by Paul Eggert.  This file is in the public domain.

# Porting notes:
#
# This script requires a Posix-like shell and prefers the extension of a
# 'select' statement.  The 'select' statement was introduced in the
# Korn shell and is available in Bash and other shell implementations.
# If your host lacks both Bash and the Korn shell, you can get their
# source from one of these locations:
#
#	Bash <http://www.gnu.org/software/bash/bash.html>
#	Korn Shell <http://www.kornshell.com/>
#	Public Domain Korn Shell <http://www.cs.mun.ca/~michael/pdksh/>
#
# For portability to Solaris 9 /bin/sh this script avoids some POSIX
# features and common extensions, such as $(...) (which works sometimes
# but not others), $((...)), and $10.
#
# This script also uses several features of modern awk programs.
# If your host lacks awk, or has an old awk that does not conform to Posix,
# you can use either of the following free programs instead:
#
#	Gawk (GNU awk) <http://www.gnu.org/software/gawk/>
#	mawk <http://invisible-island.net/mawk/>

# Specify default values for environment variables if they are unset.
: ${AWK=awk}
: ${TZDIR=/usr/share/zoneinfo}

# Output one argument as-is to standard output.
# Safer than 'echo', which can mishandle '\' or leading '-'.
say() {
    printf '%s\n' "$1"
}

# Check for awk Posix compliance.
($AWK -v x=y 'BEGIN { exit 123 }') </dev/null >/dev/null 2>&1
[ $? = 123 ] || {
	say >&2 "$0: Sorry, your '$AWK' program is not Posix compatible."
	exit 1
}

coord=
location_limit=10
zonetabtype=zone1970

usage="Usage: tzselect [--version] [--help] [-c COORD] [-n LIMIT]
Select a time zone interactively.

Options:

-c COORD
    Instead of asking for continent and then country and then city,
    ask for selection from time zones whose largest cities
    are closest to the location with geographical coordinates COORD.
    COORD should use ISO 6709 notation, for example, '-c +4852+00220'
    for Paris (in degrees and minutes, North and East), or
    '-c -35-058' for Buenos Aires (in degrees, South and West).

-n LIMIT
    Display at most LIMIT locations when -c is used (default $location_limit).

--version
    Output version information.

--help
    Output this help.

Report bugs to $REPORT_BUGS_TO."

# Ask the user to select from the function's arguments,
# and assign the selected argument to the variable 'select_result'.
# Exit on EOF or I/O error.  Use the shell's 'select' builtin if available,
# falling back on a less-nice but portable substitute otherwise.
if
  case $BASH_VERSION in
  ?*) : ;;
  '')
    # '; exit' should be redundant, but Dash doesn't properly fail without it.
    (eval 'set --; select x; do break; done; exit') </dev/null 2>/dev/null
  esac
then
  # Do this inside 'eval', as otherwise the shell might exit when parsing it
  # even though it is never executed.
  eval '
    doselect() {
      select select_result
      do
	case $select_result in
	"") echo >&2 "Please enter a number in range." ;;
	?*) break
	esac
      done || exit
    }

# Work around a bug in bash 1.14.7 and earlier, where $PS3 is sent to stdout.
    case $BASH_VERSION in
    [01].*)
      case `echo 1 | (select x in x; do break; done) 2>/dev/null` in
      ?*) PS3=
      esac
    esac
  '
else
  doselect() {
    # Field width of the prompt numbers.
    select_width=`expr $# : '.*'`

select_i=

while :
    do
      case $select_i in
      '')
	select_i=0
	for select_word
	do
	  select_i=`expr $select_i + 1`
	  printf >&2 "%${select_width}d) %s\\n" $select_i "$select_word"
	done ;;
      *[!0-9]*)
	echo >&2 'Please enter a number in range.' ;;
      *)
	if test 1 -le $select_i && test $select_i -le $#; then
	  shift `expr $select_i - 1`
	  select_result=$1
	  break
	fi
	echo >&2 'Please enter a number in range.'
      esac

# Prompt and read input.
      printf >&2 %s "${PS3-#? }"
      read select_i || exit
    done
  }
fi

while getopts c:n:t:-: opt
do
    case $opt$OPTARG in
    c*)
	coord=$OPTARG ;;
    n*)
	location_limit=$OPTARG ;;
    t*) # Undocumented option, used for developer testing.
	zonetabtype=$OPTARG ;;
    -help)
	exec echo "$usage" ;;
    -version)
	exec echo "tzselect $PKGVERSION$TZVERSION" ;;
    -*)
	say >&2 "$0: -$opt$OPTARG: unknown option; try '$0 --help'"; exit 1 ;;
    *)
	say >&2 "$0: try '$0 --help'"; exit 1 ;;
    esac
done

shift `expr $OPTIND - 1`
case $# in
0) ;;
*) say >&2 "$0: $1: unknown argument"; exit 1 ;;
esac

# Make sure the tables are readable.
TZ_COUNTRY_TABLE=$TZDIR/iso3166.tab
TZ_ZONE_TABLE=$TZDIR/$zonetabtype.tab
for f in $TZ_COUNTRY_TABLE $TZ_ZONE_TABLE
do
	<"$f" || {
		say >&2 "$0: time zone files are not set up correctly"
		exit 1
	}
done

# If the current locale does not support UTF-8, convert data to current
# locale's format if possible, as the shell aligns columns better that way.
# Check the UTF-8 of U+12345 CUNEIFORM SIGN URU TIMES KI.
! $AWK 'BEGIN { u12345 = "\360\222\215\205"; exit length(u12345) != 1 }' &&
    { tmp=`(mktemp -d) 2>/dev/null` || {
	tmp=${TMPDIR-/tmp}/tzselect.$$ &&
	(umask 77 && mkdir -- "$tmp")
    };} &&
    trap 'status=$?; rm -fr -- "$tmp"; exit $status' 0 HUP INT PIPE TERM &&
    (iconv -f UTF-8 -t //TRANSLIT <"$TZ_COUNTRY_TABLE" >$tmp/iso3166.tab) \
        2>/dev/null &&
    TZ_COUNTRY_TABLE=$tmp/iso3166.tab &&
    iconv -f UTF-8 -t //TRANSLIT <"$TZ_ZONE_TABLE" >$tmp/$zonetabtype.tab &&
    TZ_ZONE_TABLE=$tmp/$zonetabtype.tab

newline='
'
IFS=$newline

# Awk script to read a time zone table and output the same table,
# with each column preceded by its distance from 'here'.
output_distances='
  BEGIN {
    FS = "\t"
    while (getline <TZ_COUNTRY_TABLE)
      if ($0 ~ /^[^#]/)
        country[$1] = $2
    country["US"] = "US" # Otherwise the strings get too long.
  }
  function abs(x) {
    return x < 0 ? -x : x;
  }
  function min(x, y) {
    return x < y ? x : y;
  }
  function convert_coord(coord, deg, minute, ilen, sign, sec) {
    if (coord ~ /^[-+]?[0-9]?[0-9][0-9][0-9][0-9][0-9][0-9]([^0-9]|$)/) {
      degminsec = coord
      intdeg = degminsec < 0 ? -int(-degminsec / 10000) : int(degminsec / 10000)
      minsec = degminsec - intdeg * 10000
      intmin = minsec < 0 ? -int(-minsec / 100) : int(minsec / 100)
      sec = minsec - intmin * 100
      deg = (intdeg * 3600 + intmin * 60 + sec) / 3600
    } else if (coord ~ /^[-+]?[0-9]?[0-9][0-9][0-9][0-9]([^0-9]|$)/) {
      degmin = coord
      intdeg = degmin < 0 ? -int(-degmin / 100) : int(degmin / 100)
      minute = degmin - intdeg * 100
      deg = (intdeg * 60 + minute) / 60
    } else
      deg = coord
    return deg * 0.017453292519943296
  }
  function convert_latitude(coord) {
    match(coord, /..*[-+]/)
    return convert_coord(substr(coord, 1, RLENGTH - 1))
  }
  function convert_longitude(coord) {
    match(coord, /..*[-+]/)
    return convert_coord(substr(coord, RLENGTH))
  }
  # Great-circle distance between points with given latitude and longitude.
  # Inputs and output are in radians.  This uses the great-circle special
  # case of the Vicenty formula for distances on ellipsoids.
  function gcdist(lat1, long1, lat2, long2, dlong, x, y, num, denom) {
    dlong = long2 - long1
    x = cos(lat2) * sin(dlong)
    y = cos(lat1) * sin(lat2) - sin(lat1) * cos(lat2) * cos(dlong)
    num = sqrt(x * x + y * y)
    denom = sin(lat1) * sin(lat2) + cos(lat1) * cos(lat2) * cos(dlong)
    return atan2(num, denom)
  }
  # Parallel distance between points with given latitude and longitude.
  # This is the product of the longitude difference and the cosine
  # of the latitude of the point that is further from the equator.
  # I.e., it considers longitudes to be further apart if they are
  # nearer the equator.
  function pardist(lat1, long1, lat2, long2) {
    return abs(long1 - long2) * min(cos(lat1), cos(lat2))
  }
  # The distance function is the sum of the great-circle distance and
  # the parallel distance.  It could be weighted.
  function dist(lat1, long1, lat2, long2) {
    return gcdist(lat1, long1, lat2, long2) + pardist(lat1, long1, lat2, long2)
  }
  BEGIN {
    coord_lat = convert_latitude(coord)
    coord_long = convert_longitude(coord)
  }
  /^[^#]/ {
    here_lat = convert_latitude($2)
    here_long = convert_longitude($2)
    line = $1 "\t" $2 "\t" $3
    sep = "\t"
    ncc = split($1, cc, /,/)
    for (i = 1; i <= ncc; i++) {
      line = line sep country[cc[i]]
      sep = ", "
    }
    if (NF == 4)
      line = line " - " $4
    printf "%g\t%s\n", dist(coord_lat, coord_long, here_lat, here_long), line
  }
'

# Begin the main loop.  We come back here if the user wants to retry.
while

echo >&2 'Please identify a location' \
		'so that time zone rules can be set correctly.'

continent=
	country=
	region=

case $coord in
	?*)
		continent=coord;;
	'')

# Ask the user for continent or ocean.

echo >&2 'Please select a continent, ocean, "coord", or "TZ".'

quoted_continents=`
	  $AWK '
	    BEGIN { FS = "\t" }
	    /^[^#]/ {
              entry = substr($3, 1, index($3, "/") - 1)
              if (entry == "America")
		entry = entry "s"
              if (entry ~ /^(Arctic|Atlantic|Indian|Pacific)$/)
		entry = entry " Ocean"
              printf "'\''%s'\''\n", entry
            }
          ' <"$TZ_ZONE_TABLE" |
	  sort -u |
	  tr '\n' ' '
	  echo ''
	`

eval '
	    doselect '"$quoted_continents"' \
		"coord - I want to use geographical coordinates." \
		"TZ - I want to specify the time zone using the Posix TZ format."
	    continent=$select_result
	    case $continent in
	    Americas) continent=America;;
	    *" "*) continent=`expr "$continent" : '\''$[^ ]*$'\''`
	    esac
	'
	esac

case $continent in
	TZ)
		# Ask the user for a Posix TZ string.  Check that it conforms.
		while
			echo >&2 'Please enter the desired value' \
				'of the TZ environment variable.'
			echo >&2 'For example, GST-10 is a zone named GST' \
				'that is 10 hours ahead (east) of UTC.'
			read TZ
			$AWK -v TZ="$TZ" 'BEGIN {
				tzname = "(<[[:alnum:]+-]{3,}>|[[:alpha:]]{3,})"
				time = "(2[0-4]|[0-1]?[0-9])" \
				  "(:[0-5][0-9](:[0-5][0-9])?)?"
				offset = "[-+]?" time
				mdate = "M([1-9]|1[0-2])\\.[1-5]\\.[0-6]"
				jdate = "((J[1-9]|[0-9]|J?[1-9][0-9]" \
				  "|J?[1-2][0-9][0-9])|J?3[0-5][0-9]|J?36[0-5])"
				datetime = ",(" mdate "|" jdate ")(/" time ")?"
				tzpattern = "^(:.*|" tzname offset "(" tzname \
				  "(" offset ")?(" datetime datetime ")?)?)$"
				if (TZ ~ tzpattern) exit 1
				exit 0
			}'
		do
		    say >&2 "'$TZ' is not a conforming Posix time zone string."
		done
		TZ_for_date=$TZ;;
	*)
		case $continent in
		coord)
		    case $coord in
		    '')
			echo >&2 'Please enter coordinates' \
				'in ISO 6709 notation.'
			echo >&2 'For example, +4042-07403 stands for'
			echo >&2 '40 degrees 42 minutes north,' \
				'74 degrees 3 minutes west.'
			read coord;;
		    esac
		    distance_table=`$AWK \
			    -v coord="$coord" \
			    -v TZ_COUNTRY_TABLE="$TZ_COUNTRY_TABLE" \
			    "$output_distances" <"$TZ_ZONE_TABLE" |
		      sort -n |
		      sed "${location_limit}q"
		    `
		    regions=`say "$distance_table" | $AWK '
		      BEGIN { FS = "\t" }
		      { print $NF }
		    '`
		    echo >&2 'Please select one of the following' \
			    'time zone regions,'
		    echo >&2 'listed roughly in increasing order' \
			    "of distance from $coord".
		    doselect $regions
		    region=$select_result
		    TZ=`say "$distance_table" | $AWK -v region="$region" '
		      BEGIN { FS="\t" }
		      $NF == region { print $4 }
		    '`
		    ;;
		*)
		# Get list of names of countries in the continent or ocean.
		countries=`$AWK \
			-v continent="$continent" \
			-v TZ_COUNTRY_TABLE="$TZ_COUNTRY_TABLE" \
		'
			BEGIN { FS = "\t" }
			/^#/ { next }
			$3 ~ ("^" continent "/") {
			    ncc = split($1, cc, /,/)
			    for (i = 1; i <= ncc; i++)
				if (!cc_seen[cc[i]]++) cc_list[++ccs] = cc[i]
			}
			END {
				while (getline <TZ_COUNTRY_TABLE) {
					if ($0 !~ /^#/) cc_name[$1] = $2
				}
				for (i = 1; i <= ccs; i++) {
					country = cc_list[i]
					if (cc_name[country]) {
					  country = cc_name[country]
					}
					print country
				}
			}
		' <"$TZ_ZONE_TABLE" | sort -f`

# If there's more than one country, ask the user which one.
		case $countries in
		*"$newline"*)
			echo >&2 'Please select a country' \
				'whose clocks agree with yours.'
			doselect $countries
			country=$select_result;;
		*)
			country=$countries
		esac

# Get list of names of time zone rule regions in the country.
		regions=`$AWK \
			-v country="$country" \
			-v TZ_COUNTRY_TABLE="$TZ_COUNTRY_TABLE" \
		'
			BEGIN {
				FS = "\t"
				cc = country
				while (getline <TZ_COUNTRY_TABLE) {
					if ($0 !~ /^#/  &&  country == $2) {
						cc = $1
						break
					}
				}
			}
			/^#/ { next }
			$1 ~ cc { print $4 }
		' <"$TZ_ZONE_TABLE"`

# If there's more than one region, ask the user which one.
		case $regions in
		*"$newline"*)
			echo >&2 'Please select one of the following' \
				'time zone regions.'
			doselect $regions
			region=$select_result;;
		*)
			region=$regions
		esac

# Determine TZ from country and region.
		TZ=`$AWK \
			-v country="$country" \
			-v region="$region" \
			-v TZ_COUNTRY_TABLE="$TZ_COUNTRY_TABLE" \
		'
			BEGIN {
				FS = "\t"
				cc = country
				while (getline <TZ_COUNTRY_TABLE) {
					if ($0 !~ /^#/  &&  country == $2) {
						cc = $1
						break
					}
				}
			}
			/^#/ { next }
			$1 ~ cc && $4 == region { print $3 }
		' <"$TZ_ZONE_TABLE"`
		esac

# Make sure the corresponding zoneinfo file exists.
		TZ_for_date=$TZDIR/$TZ
		<"$TZ_for_date" || {
			say >&2 "$0: time zone files are not set up correctly"
			exit 1
		}
	esac

# Use the proposed TZ to output the current date relative to UTC.
	# Loop until they agree in seconds.
	# Give up after 8 unsuccessful tries.

extra_info=
	for i in 1 2 3 4 5 6 7 8
	do
		TZdate=`LANG=C TZ="$TZ_for_date" date`
		UTdate=`LANG=C TZ=UTC0 date`
		TZsec=`expr "$TZdate" : '.*:$[0-5][0-9]$'`
		UTsec=`expr "$UTdate" : '.*:$[0-5][0-9]$'`
		case $TZsec in
		$UTsec)
			extra_info="
Selected time is now:	$TZdate.
Universal Time is now:	$UTdate."
			break
		esac
	done

# Output TZ info and ask the user to confirm.

echo >&2 ""
	echo >&2 "The following information has been given:"
	echo >&2 ""
	case $country%$region%$coord in
	?*%?*%)	say >&2 "	$country$newline	$region";;
	?*%%)	say >&2 "	$country";;
	%?*%?*) say >&2 "	coord $coord$newline	$region";;
	%%?*)	say >&2 "	coord $coord";;
	*)	say >&2 "	TZ='$TZ'"
	esac
	say >&2 ""
	say >&2 "Therefore TZ='$TZ' will be used.$extra_info"
	say >&2 "Is the above information OK?"

doselect Yes No
	ok=$select_result
	case $ok in
	Yes) break
	esac
do coord=
done

case $SHELL in
*csh) file=.login line="setenv TZ '$TZ'";;
*) file=.profile line="TZ='$TZ'; export TZ"
esac

test -t 1 && say >&2 "
You can make this change permanent for yourself by appending the line
	$line
to the file '$file' in your home directory; then log out and log in again.

Here is that TZ value again, this time on standard output so that you
can use the $0 command in shell scripts:"

say "$TZ"

Current path /usr/bin

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✏️ tzselect