yyyymmddHHMMSSな時刻文字列をunixタイムに変換するbashシェルスクリプト

2021 Mar. 11.
2021 Jan. 17.

Datetime='20210117175000'
Year=${Datetime:0:4}
Month=${Datetime:4:2}
Day=${Datetime:6:2}
Hour=${Datetime:8:2}
Minute=${Datetime:10:2}
Second=${Datetime:12:2}
DatetimeFormated="${Year}-${Month}-${Day} ${Hour}:${Minute}:${Second}"
DatetimeUnix=`date -d "${DatetimeFormated}" +%s`