We all know that this is not a satisfactory documentation for
ed, but it is better than nothing.`
Use the additional help from within ed available at the commands 'h' 
and 'h<command_you_are_interested_in>'.

When in 'ed', the prompt is ':'.

Ed has two modes, command mode and insert mode. The insert mode has
no prompt. You exit the insert mode by typing a single '.' on a line.

All commands have the following syntax:

  X,Ycmd

or

  Xcmd

For example:

  1,10p
    Will print line 1 to 10.
  1,5d
    Will delete line 1 to 5.
  8p
    Will print line 8.

A '.' is the "current line". The current line is the last line
referenced. If you want to print last line + 10 more:
.,.+10p


Ed knows the following commands:

	/	search forward for pattern
	?	search backward for a pattern
	=	show current line number
	a	append text starting after this line
	A	like 'a' but with inverse autoindent mode
	c	change current line, query for replacement text
	d	delete line(s)
	e	replace this file with another file
	E	same as 'e' but works if file has been modified
	f	show/change current file name
	g	Search and execute command on any matching line.
	h	help file (display this list)
	i	insert text starting before this line
	I	indent the entire file (from DGD ed v0.1)
	j	join lines together
	k	mark this line with a character - later referenced as 'a
	l	line line(s) with control characters displayed
	m	move line(s) to specified line
	n	toggle line numbering
	p	print line(s) in range
	q	quit editor
	Q	quit editor even if file modified and not saved
	r	read file into editor at end of file or behind the given line
	s	search and replace
	set	query, change or save option settings
	t	move copy of line(s) to specified line
	v	Search and execute command on any non-matching line.
	x	save file and quit
	w	write to current file (or specified file)
	W	like the 'w' command but appends instead
	z	display 20 lines, possible args are . + -
	Z	display 40 lines, possible args are . + -

As line numbers '.' is current line, and '$' is last line of file.
Thus '1,$p' will always print all of the file.

Searching is done with /text/:

  /hello/
    Finds first line after current line holding 'hello' in it.

Just // will repeat the search.

Substitutions are very advanced.

First a simple example:

  s/apa/bepa/
    This will substitue the 'apa' in current line to 'bepa'.
    If an 'p' is appended, you will also immediately see the result.

  1,$s/apa/bepa/
    Same, but all lines in file. Only first occurence on every line.

  Any character can used instead of '/':
    s!apa!bepa!g
  The 'g' specifies that all occurences of apa on this line are
  changed to bepa. 

The pattern that are supposed to be replaced, can be a regular
expression. Regular expressions assign certain matching function to
some special letters:

        . Match any character.
        ^ Match begin of line.
        $ Match end of line.
        \< Match begin of word.
        \> Match end of word.
        x|y Match regexp x or regexp y.
        () Match enclosed regexp like a 'simple' one.
        x* Match any number (0 or more) of regexp x.
        [..] Match one of the characters enclosed.
        [^ ..] Match none of the characters enclosed. 
           The .. are to replaced by single characters or character ranges:
           [abc] matches a, b or c.
           [ab0-9] matches a, b or any digit.
           [^a-z] does not match any lowercase character.
        
        \c match character c even if it's one of the special characters.

Example:

  s/ab.d/ABCD/
    Substitute any string 'abXd' against 'ABCD' where X can be any character.