What command would you use to copy a file?

The command used to copy a file in a Linux environment is 'cp'. This command stands for 'copy' and allows users to create a duplicate of a specified file or directory. When using 'cp', you can copy files by specifying the source file and the destination where you want the copy to be placed.

For example, the command cp source.txt destination.txt would create a copy of 'source.txt' named 'destination.txt'. This command can also work with directories when used with the '-r' option, allowing for recursive copying.

While other options may serve different purposes—'mv' is used for moving or renaming files, 'rsync' is typically employed for synchronizing files and directories between different locations, and 'diff' is utilized to compare files and show the differences—'cp' is specifically designed for copying files, making it the correct choice for the question.