shell 時間循環

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$cat tt.sh 
#!/bin/bash

start=`date +%s -d "2017-02-27 00:00:00"`
end=`date +%s -d "2017-02-28 00:00:00"`

while [ "$start" -le "$end" ]
    do
        day=`date -d @$start "+%Y%m%d"`
        echo $day
        start=$((start+86400))
    done