ed was created, along with the Unix operating system, by Ken
Thompson and Dennis Ritchie. It is the refinement of its more complex,
programmable predecessor, QED, to which Thompson and Ritchie had
already added pattern matching capabilities (see Regular expressions).
For the purposes of this tutorial, a working knowledge of the Unix shell
sh and the Unix file system is recommended, since ed
is designed to interact closely with them.
(See the
bash manual
for details about bash).
The principal difference between line editors and display editors is
that display editors provide instant feedback to user commands, whereas
line editors require sometimes lengthy input before any effects are
seen. The advantage of instant feedback, of course, is that if a mistake
is made, it can be corrected immediately, before more damage is done.
Editing in ed requires more strategy and forethought; but if
you are up to the task, it can be quite efficient.
Much of the ed command syntax is shared with other Unix utilities.
As with the shell, RETURN (the carriage-return key) enters a line
of input. So when we speak of "entering" a command or some text in
ed, RETURN is implied at the end of each line. Prior to
typing RETURN, corrections to the line may be made by typing
either BACKSPACE to erase characters backwards, or CONTROL-u
(i.e., hold the CONTROL key and type u) to erase the whole line.
When ed first opens, it expects to be told what to do but
doesn’t prompt us like the shell. So let’s begin by telling ed
to do so with the P (prompt) command:
$ ed P *
By default, ed uses asterisk (‘*’) as command prompt to avoid
confusion with the shell command prompt (‘$’).
We can run Unix shell (sh) commands from inside ed by
prefixing them with ! (exclamation mark, aka "bang"). For example:
*!date Mon Jun 26 10:08:41 PDT 2006 ! *!for s in hello world; do echo $s; done hello world ! *
So far, this is no different from running commands in the Unix shell.
But let’s say we want to edit the output of a command, or save it to a
file. First we must capture the command output to a temporary location
called a buffer where ed can access it. This is done
with ed’s r command (mnemonic: read):
*r !cal -m 137 *
Here ed is telling us that it has just read 137 characters
into the editor buffer - i.e., the output of the cal command,
which prints a simple ASCII calendar. To display the buffer contents we
issue the p (print) command (not to be confused with the
prompt command, which is uppercase!). To indicate the range of lines in
the buffer that should be printed, we prefix the command with ,
(comma) which is shorthand for "the whole buffer":
*,p
June 2006
Mo Tu We Th Fr Sa Su
1 2 3 4
5 6 7 8 9 10 11
12 13 14 15 16 17 18
19 20 21 22 23 24 25
26 27 28 29 30
*
Now let’s write the buffer contents to a file named ‘junk’ with the w (write) command:
*w junk 137 *
Need we say? It’s good practice to frequently write the buffer contents,
since unwritten changes to the buffer will be lost when we exit ed.
The sample sessions below illustrate some basic concepts of line editing
with ed. We begin by creating a file, sonnet, with some
help from Shakespeare. As with the shell, all input to ed must
be followed by a newline character. Commands beginning with
‘#’ are taken as comments and ignored. Input mode lines that begin
with ‘#’ are just more input.
$ ed # The 'a' command is for appending text to the editor buffer. a No more be grieved at that which thou hast done. Roses have thorns, and filvers foutians mud. Clouds and eclipses stain both moon and sun, And loathsome canker lives in sweetest bud. . # Entering a single period on a line returnsedto command mode. # Now write the buffer to the file sonnet and quit: w sonnet 183 #edreports the number of characters written. q $ ls -l total 2 -rw-rw-r-- 1 alm 183 Nov 10 01:16 sonnet $
In the next example, some typos are corrected in the file sonnet.
$ ed sonnet 183 # Begin by printing the buffer to the terminal with the ‘p’ command. # The ',' means "all lines". ,p No more be grieved at that which thou hast done. Roses have thorns, and filvers foutians mud. Clouds and eclipses stain both moon and sun, And loathsome canker lives in sweetest bud. # Select line 2 for editing. 2 Roses have thorns, and filvers foutians mud. # Use the substitute command, ‘s’, to replace 'filvers' with 'silver', # and print the result. s/filvers/silver/p Roses have thorns, and silver foutians mud. # And correct the spelling of 'fountains'. s/utia/untai/p Roses have thorns, and silver fountains mud. w sonnet 183 q $
Since ed is line-oriented, we have to tell it which line, or
range of lines we want to edit. In the example above, we do this by
specifying the line’s number, or sequence in the buffer. Alternatively,
we could have specified a unique string in the line, e.g.,
‘/filvers/’, where the ‘/’s delimit the string in question.
Subsequent commands affect only the selected line, a.k.a. the
current line. Portions of that line are then replaced with the
substitute command, whose syntax is ‘s/old/new/’.
Although ed accepts only one command per line, the print command
‘p’ is an exception, and may be appended to the end of most commands.
In the next example, a title is added to our sonnet.
$ ed sonnet 183 a Sonnet #50 . ,p No more be grieved at that which thou hast done. Roses have thorns, and silver fountains mud. Clouds and eclipses stain both moon and sun, And loathsome canker lives in sweetest bud. Sonnet #50 # The title got appended to the end; we should have used '0a' # to append "before the first line". # Move the title to its proper place. 5m0p Sonnet #50 # The title is now the first line, and the current address has been # set to the address of this line as well. ,p Sonnet #50 No more be grieved at that which thou hast done. Roses have thorns, and silver fountains mud. Clouds and eclipses stain both moon and sun, And loathsome canker lives in sweetest bud. wq sonnet 195 $
When ed opens a file, the current address is initially set to
the address of the last line of that file. Similarly, the move command
‘m’ sets the current address to the address of the last line moved.
Related programs or routines are vi(1), sed(1),
regex(3), sh(1). Relevant documents are:
Unix User’s Manual Supplementary Documents: 12 — 13
B. W. Kernighan and P. J. Plauger: "Software Tools in Pascal", Addison-Wesley, 1981.