1.  Starting ex

      Each instance of the editor has a set of options, which can be set to tailor it to your liking. The command edit invokes a version of ex designed for more casual or beginning users by changing the default settings of some of these options. To simplify the description which follows we assume the default settings of the options.

      When invoked, ex determines the terminal type from the TERM variable in the environment. It there is a TERMCAP variable in the environment, and the type of the terminal described there matches the TERM variable, then that description is used. Also if the TERMCAP variable contains a pathname (beginning with a /) then the editor will seek the description of the terminal in that file (rather than the default /etc/termcap). If there is a variable EXINIT in the environment, then the editor will execute the commands in that variable, otherwise if there is a file .exrc in your HOME directory ex reads commands from that file, simulating a source command. Option setting commands placed in EXINIT or .exrc will be executed before each editor session.

      A command to enter ex has the following prototype:**

ex [ - ] [ -v ] [ -t tag ] [ -r ] [ -l ] [ -wn ] [ -x ] [ -R ] [ +command ] name ...
The most common case edits a single file with no options, i.e.:
ex name
The - command line option option suppresses all interactive-user feedback and is useful in processing editor scripts in command files. The -v option is equivalent to using vi rather than ex. The -t option is equivalent to an initial tag command, editing the file containing the tag and positioning the editor at its definition. The -r option is used in recovering after an editor or system crash, retrieving the last saved version of the named file or, if no file is specified, typing a list of saved files. The -l option sets up for editing LISP, setting the showmatch and lisp options. The -w option sets the default window size to n, and is useful on dialups to start in small windows. The -x option causes ex to prompt for a key, which is used to encrypt and decrypt the contents of the file, which should already be encrypted using the same key, see crypt(1). The -R option sets the readonly option at the start. Name arguments indicate files to be edited. An argument of the form +command indicates that the editor should begin by executing the specified command. If command is omitted, then it defaults to ``$'', positioning the editor at the last line of the first file initially. Other useful commands here are scanning patterns of the form ``/pat'' or line numbers, e.g. ``+100'' starting at line 100.