Generate a date+hour sequence with a given date - bash

Question

Given a date in format 20130522, I need to generate a sequence of date+hour as below:
2013052112,2013052113,2013052114,...,2013052122,2013052123,
2013052200,2013052201,2013052202,...,2013052222,2013052223,
2013052300
in which the first date+hour is 12 hours before the given date and the last date+hour is the midnight in the next day of the given date.
I tried several ways but none of them is ideal. How to generate such a sequence in a clean way using shell script? Thanks!
--Edit--
Per your request, this is what I have so far:
day=20130522
begin=`date --date "$day -12 hours"`
begin=`date -d "${begin:0:8} ${begin:8:2}" +%s`
end=`date --date "$day +1 day"`
end=`date -d "${end:0:8} ${end:8:2}" +%s`
datestr=`date -d #${begin} +%Y%m%d%H`
let begin=$begin+3600
while [ $begin -le $end ]
do
hr=`date -d #${begin} +%Y%m%d%H`
datestr="$datestr,$hr"
let begin=$begin+3600
done
and this is what I got from above:
2013052100,2013052101,2013052102,...,2013052123,
2013052200,2013052201,2013052202,...,2013052223,
2013052300

Answer 1

You can use date and brace expansion:
date=20130522
echo $(date -d "-1 day $date" +%Y%m%d){12..23} \
"$date"{00..23} \
$(date -d "+1 day $date" +%Y%m%d)00
Output (wrapped):
2013052112 2013052113 2013052114 2013052115 2013052116 2013052117 2013052118 2013052119 2013052120
2013052121 2013052122 2013052123 2013052200 2013052201 2013052202 2013052203 2013052204 2013052205
2013052206 2013052207 2013052208 2013052209 2013052210 2013052211 2013052212 2013052213 2013052214
2013052215 2013052216 2013052217 2013052218 2013052219 2013052220 2013052221 2013052222 2013052223
2013052300

Answer 2

Your code was quite well. What I think is that you used so much bash conversion, while date is very powerful and handles in an easier way.
I rewrited something and now I get this:
day=20130522
begin=$(date --date "$day -12 hours" "+%s")
end=$(date --date "$day +1 day" "+%s")
hr=$(date --date "#$begin" "+%s")
while [[ $hr -lt $end ]]
do
hr=$(($hr + 3600))
echo $(date -d "#$hr" "+%Y%m%d %H")
done
$ ./script
20130521 13
20130521 14
.../...
20130522 22
20130522 23
20130523 00