2.  File manipulation

2.1.  Current file

      Ex is normally editing the contents of a single file, whose name is recorded in the current file name. Ex performs all editing actions in a buffer (actually a temporary file) into which the text of the file is initially read. Changes made to the buffer have no effect on the file being edited unless and until the buffer contents are written out to the file with a write command. After the buffer contents are written, the previous contents of the written file are no longer accessible. When a file is edited, its name becomes the current file name, and its contents are read into the buffer.

      The current file is almost always considered to be edited. This means that the contents of the buffer are logically connected with the current file name, so that writing the current buffer contents onto that file, even if it exists, is a reasonable action. If the current file is not edited then ex will not normally write on it if it already exists.*

2.2.  Alternate file

      Each time a new value is given to the current file name, the previous current file name is saved as the alternate file name. Similarly if a file is mentioned but does not become the current file, it is saved as the alternate file name.

2.3.  Filename expansion

      Filenames within the editor may be specified using the normal shell expansion conventions. In addition, the character `%' in filenames is replaced by the current file name and the character `#' by the alternate file name.**

2.4.  Multiple files and named buffers

      If more than one file is given on the command line, then the first file is edited as described above. The remaining arguments are placed with the first file in the argument list. The current argument list may be displayed with the args command. The next file in the argument list may be edited with the next command. The argument list may also be respecified by specifying a list of names to the next command. These names are expanded, the resulting list of names becomes the new argument list, and ex edits the first file on the list.

      For saving blocks of text while editing, and especially when editing more than one file, ex has a group of named buffers. These are similar to the normal buffer, except that only a limited number of operations are available on them. The buffers have names a through z.***

2.5.  Read only

      It is possible to use ex in read only mode to look at files that you have no intention of modifying. This mode protects you from accidently overwriting the file. Read only mode is on when the readonly option is set. It can be turned on with the -R command line option, by the view command line invocation, or by setting the readonly option. It can be cleared by setting noreadonly. It is possible to write, even while in read only mode, by indicating that you really know what you are doing. You can write to a different file, or can use the ! form of write, even while in read only mode.