通常我们要查询本地区当前的日期和时间，可以使用到最基本的date命令。但是如果你要要穿越不同的时区，这时不就遇到麻烦了？或者，更有说服力点，如果你有朋友和同事在不同的国家地区，而且你很在乎时间，比如在卡萨布兰加，梵谛冈市或者悉尼。
现在我们在大多数Unix机可以通过date命令来创建一个时区数据库。它通常位于/usr/share/zoneinfo，该数据库列举了多达250个不同的区域，并且为每个区域确定适当的时区。因为date命令可以TZ选项指定时区，而且适合任何的已知区域，下面举例该功能的应用：
$ TZ="Africa/Casablanca" date
Mon Dec 2 16:31:01 WET 2069
但是我们可以使用一个shell脚本，生成更友好的时区数据库：暂时的环境变量设置可能对大多数系统使用者觉得不大舒服。
脚本源代码
#!/bin/sh
# timein - Shows the current time in the specified time zone or
# geographic zone. Without any argument, shows UTC/GMT. Use
# the word "list" to see a list of known geographic regions.
# Note that it's possible to match zone directories (regions),
# but that only time zone files (cities) are valid specifications.
# Time zone database ref: http://www.twinsun.com/tz/tz-link.htm
zonedir="/usr/share/zoneinfo"
if [ ! -d $zonedir ] ; then
echo "No time zone database at $zonedir." >&2 ; exit 1
fi
if [ -d "$zonedir/posix" ] ; then
zonedir=$zonedir/posix # modern Linux systems
fi
if [ $# -eq 0 ] ; then
timezone="UTC"
mixedzone="UTC"
elif [ "$1" = "list" ] ; then
( echo "All known time zones and regions defined on this system:"
cd $zonedir
find * -type f -print | xargs -n 2 | \
awk '{ printf " %-38s %-38s\n", $1, $2 }'
) | more
exit 0
else
region="$(dirname $1)"
zone="$(basename $1)"
# Is it a direct match? If so, we're good to go. Otherwise we need
# to dig around a bit to find things. Start by just counting matches.
matchcnt="$(find $zonedir -name $zone -type f -print |
wc -l | sed 's/[^[:digit:]]//g')"
if [ "$matchcnt" -gt 0 ] ; then # at least one file matches
if [ $matchcnt -gt 1 ] ; then # more than one file matches
echo "\"$zone\" matches more than one possible time zone record." >&2
echo "Please use 'list' to see all known regions and time zones" >&2
exit 1
fi
match="$(find $zonedir -name $zone -type f -print)"
mixedzone="$zone"
else
# First letter capitalized, rest of word lowercase for region + zone
mixedregion="$(echo ${region%${region#?}} | tr '[[:lower:]]' '[[:upper:]]')\
$(echo ${region#?} | tr '[[:upper:]]' '[[:lower:]]')"
mixedzone="$(echo ${zone%${zone#?}} | tr '[[:lower:]]' '[[:upper:]]')\
$(echo ${zone#?} | tr '[[:upper:]]' '[[:lower:]]')"
if [ "$mixedregion" != "." ] ; then
# Only look for specified zone in specified region
# to let users specify unique matches when there's more than one
# possibility (e.g., "Atlantic")
match="$(find $zonedir/$mixedregion -type f -name $mixedzone -print)"
else
match="$(find $zonedir -name $mixedzone -type f -print)"
fi
if [ -z "$match" ] ; then # no file matches specified pattern
if [ ! -z $(find $zonedir -name $mixedzone -type d -print) ] ; then
echo \
"The region \"$1\" has more than one time zone. Please use 'list'" >&2
else # just not a match at all
echo "Can't find an exact match for \"$1\". Please use 'list'" >&2
fi
echo "to see all known regions and time zones." >&2
exit 1
fi
fi
timezone="$match"
fi
nicetz=$(echo $timezone | sed "s|$zonedir/||g") # pretty up the output
echo It\'s $(TZ=$timezone date '+%A, %B %e, %Y, at %l:%M %p') in $nicetz
exit 0
工作原理
运行脚本
指定某个特定的时区或城市进行查询，在命令返回结果就会显示该时区或城市的时间。只要你对相关的时区或城市有所了解，在该脚本就就能用时区或城市查询，比如用Pacific或Yap。如果没附带任何选项，timein脚本就显示通用时间，即格林威治标准时间(UTC)
结果
$ timein
It's Friday, March 28, 2069, at 2:58 AM in UTC
$ timein London
It's Friday, March 28, 2069, at 2:58 AM in Europe/London
$ timein Brazil
The region "Brazil" has more than one time zone. Please use 'list'
to see all known regions and time zones.
$ timein Pacific/Honolulu
It's Thursday, March 27, 2069, at 4:58 PM in Pacific/Honolulu
$ timein WET
It's Friday, March 28, 2069, at 3:58 AM in WET
$ timein mycloset
Can't find an exact match for "mycloset". Please use 'list'
to see all known regions and time zones.
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