how would you copy a file?

[Skaperen]

suppose your project is to create a script to copy a list of files from A to B only if the file does not already exist at B. you would iterate over the list, and test if it exists at B. if it does not exist at B then you will copy the file. would you write code to open the source and destination files and read/write all the contents, or would you invoke the local file copy command to do it?