In any sane editor:

Save a file - CRTL-S

In VI:

1. Switch to command mode by pressing the Esc key.

2. Type : (colon). This will open the prompt bar in the bottom left corner of the window.

3. Type w after the colon and hit Enter.

In Emacs:

https://www.gnu.org/software/emacs/manual/html_node/emacs/Save-Commands.html

C-x C-s Save the current buffer to its file (save-buffer).

C-x s Save any or all buffers to their files (save-some-buffers).

M-~ Forget that the current buffer has been changed (not-modified). With prefix argument (C-u), mark the current buffer as changed.

C-x C-w Save the current buffer with a specified file name (write-file).

M-x set-visited-file-name Change the file name under which the current buffer will be saved.

When you wish to save the file and make your changes permanent, type C-x C-s (save-buffer). After saving is finished, C-x C-s displays a message like this:

Wrote /u/rms/gnu/gnu.tasks

If the current buffer is not modified (no changes have been made in it since the buffer was created or last saved), saving is not really done, because it would have no effect. Instead, C-x C-s displays a message like this in the echo area:

(No changes need to be saved) With a prefix argument, C-u C-x C-s, Emacs also marks the buffer to be backed up when the next save is done. See Backup Files.

The command C-x s (save-some-buffers) offers to save any or all modified buffers. It asks you what to do with each buffer. The possible responses are analogous to those of query-replace:

y SPC Save this buffer and ask about the rest of the buffers.

n DEL Don’t save this buffer, but ask about the rest of the buffers.

! Save this buffer and all the rest with no more questions.

q RET Terminate save-some-buffers without any more saving.

. Save this buffer, then exit save-some-buffers without even asking about other buffers.

C-r View the buffer that you are currently being asked about. When you exit View mode, you get back to save-some-buffers, which asks the question again.

C-f Exit save-some-buffers and visit the buffer that you are currently being asked about.

d Diff the buffer against its corresponding file, so you can see what changes you would be saving. This calls the command diff-buffer-with-file (see Comparing Files).

C-h Display a help message about these options.