Copy and append data from .dat file

[Makada]

Hi,

Ill try to explain what i want to do

I have a datalogger which output a .dat file which has a maximum of 19 days worth of data.
When new data is written to the .dat file (and it has already 19 days worth of data) the first dataline (at the beginning of the .dat file) is removed to make place for the new dataline (on the end/bottom of the .dat file).

What i want is another .dat file with unlimited days of data.
So the new .dat file has to store and append all data from the source .dat file without removing the oldest data like in the source .dat file.
And it has to watch for/write missing data when the python script with the above function hasnt been running for some time, so it will look for missing data in the source .dat file and write that data in the new .dat file, appended.
The source file is updating every minute.
Maybe an example of python script code can be shown?

The source is : "C:\\Campbellsci\\Loggernet\\CR1000_Table1.dat"
The destination is :"C\\Users\\Mark\\Desktop\\CR1000_Table1.dat"

Im using Windows 10 python 3.8


Thanks.