articles/ed.md: basic ed tutorial

articles/ed.md

@@ -8,4 +8,76 @@ machine was through a teletype. Video terminals were a luxury in that time.
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 ## Tutorial
+Executing ed:
+```sh
+$ ed
+$ # Or specifying a file to open:
+$ ed file.txt
+```
+If you pass a file to ed and if it exists, it will print its size in bytes, and if the file does not
+exist ed may complain about it (at least on [GNU](gnu.md) ed).
+Unless you specify a prompt with the `-p` flag, you will only get an empty line. Here, ed is waiting
+for a command. An example basic session is shown below:
+
+```
+a
+Hello from the standard text EDitor!
+.
+w file.txt
+37
+q
+```
+First we enter into file **a**ppending mode, in which ed will begin accepting input
+for writing into the file. To tell ed that we finished typing text, we write a single `.`
+on its own line; this returns ed into command mode, then with the `w` command we save the
+text to the file `file.txt` and finally we **q**uit ed by using the `q` command.
+
+To select a specific line, we simply type its number; ed will print the line and select it
+for operations such as substitution. For example, here is how we would use the `s` command:
+```
+37
+1
+Hello from the standard text EDitor!
+s/Hello/Hi/
+1
+Hi from the standard text EDitor!
+wq
+34
+```
+
+### Command summary
+- `a`: append a line, after the current line
+- `i`: insert a line, before the current line
+- `d`: delete a line
+- `p`: prints the content of the whole buffer.
+- `s`: **s**ubstitute text in the current selected line.
+- `w`: write buffer to the file, optionally accepts a filename if it wasn't specified when launching ed.
+- `q`: quits ed
+- `wq`: write and quit
+- `!`: execute a shell command
+- `r !`: appends the output of a shell command into the buffer (the space between `r` and `!` is relevant)
+- ...
+
+Commands like `a`, `i`, `d`, `p`, `s` and others can be preceded by a line number or range (in the form `x,y`),
+with the character `,` being equivalent to the current line.
+For example, here's how we can delete multiple lines:
+```
+a
+extra line
+.
+a
+another extra line
+.
+,p
+Hi from the standard text EDitor!
+extra line
+another extra line
+2,3d
+,p
+Hi from the standard text EDitor!
+```
+
+If you ever used a [vi](vi.md) editor, ed commands should be quite familiar. After all, vi is a visual
+form of the `ex` editor (an extension to ed by Berkley).
+
 TODO