C-X C-F (set-file-name)

This command prompts in the echo line for a file name, If the file already exists, the command asks the user if this is OK. If the user says yes, the file name entered by the user becomes the new associated file name for the current buffer.

C-X C-R (file-read)

This command prompts in the echo line for a file name, then it deletes all of the text in the current buffer and reads in the file. The associated file name is set to the name of the file just read. The number of lines read is displayed in the echo line.

C-X C-I (file-insert)

This command prompts in the echo line for a file name, then reads in the file, inserting its contents at the dot in the current buffer. The number of lines read is displayed in the echo line. The file name associated with the current buffer is not changed.

C-X C-S, F2 (file-save)

This command writes the contents of the current buffer to its associated file. The "changed" flag for the current buffer is cleared. It is an error to use this command in a buffer which lacks an associated file name. This command is a no-operation if the buffer has not been changed since the last write.

C-X C-V, F3 (file-visit)

This command selects a file for editing. It prompts for a file name in the echo line. It then looks through all of the buffers for a buffer whose associated file name is the same as the file being selected. If a buffer is found, it just switches to that buffer. Otherwise it creates a new buffer, fabricating a name from the last part of the new file name, reads the file into it, and switches to the buffer.

If the desired new buffer name is not unique (perhaps you tried to visit a file in some other directory with the same name as a file already read in) the command will create a buffer with a name formed by adding a ".N" suffix, where N is a number chosen to make a unique name.

If you provide a numeric prefix to this command with Ctrl-U (or just a single Ctrl-U), the command will mark the buffer as read-only. You can toggle the read-only flag with the toggle-readonly command (C-X C-Q).

C-X C-W (file-write)

This command prompts in the echo line for a file name, then it writes the contents of the current buffer to that file. If the file already exists, the command prompts for overwrite confirmation. The "changed" flag for the current buffer is reset, and the supplied file name becomes the associated file name for the current buffer.