Final answer:
To rename a file 'new' to file 'old' in the command line, use the 'mv' command.
Step-by-step explanation:
To rename file 'new' to file 'old' in the command line, you can use the 'mv' command. The correct command would be mv new old.
This command moves or renames a file by changing its name from 'new' to 'old'. The 'mv' command is a common command in Unix-like operating systems and is used to manipulate files and directories.
It's important to note that if a file named 'old' already exists, the 'mv' command will overwrite it with the contents of the file 'new'. Make sure to use caution when using this command to avoid unintended consequences.