Formato de fechas

        Format/result                   |       Command              
        --------------------------------+----------------------------
        YYYY-MM-DD_hh:mm:ss             | date +%F_%T                
        YYYYMMDD_hhmmss                 | date +%Y%m%d_%H%M%S        
        YYYYMMDD_hhmmss (UTC version)   | date --utc +%Y%m%d_%H%M%SZ 
        YYYYMMDD_hhmmss (with local TZ) | date +%Y%m%d_%H%M%S%Z      
        YYYYMMSShhmmss                  | date +%Y%m%d%H%M%S         
        YYYYMMSShhmmssnnnnnnnnn         | date +%Y%m%d%H%M%S%N       
        YYMMDD_hhmmss                   | date +%y%m%d_%H%M%S        
        Seconds since UNIX epoch:       | date +%s                   
        Nanoseconds only:               | date +%N                   
        Nanoseconds since UNIX epoch:   | date +%s%N                 
        ISO8601 UTC timestamp           | date --utc +%FT%TZ         
        ISO8601 UTC timestamp + ms      | date --utc +%FT%T.%3NZ     
        ISO8601 Local TZ timestamp      | date +%FT%T%Z              
        ISO8601 Para MongoDB            | date +"%Y-%m-%dT%H:%M:%S%z"

Ver una fecha que viene en formato raro
date -d 2017-11-06T08:50:40-0300

Convertir fecha a formato raro
date -d "2017-11-21 12:00:00" +"%Y-%m-%dT%H:%M:%S%z"