Using ed: The Standard Editor
Before you start using ed
Read this before you read the rest of the qref. You will probably never need to use ed. You should avoid using ed at all costs. You should use vim or emacs instead of ed because it is VERY user-UNfriendly. Consider yourself warned.
Intro
Commands to ed are entered by pressing a single letter, followed
by the <enter> key. Most of those commands can (optionally) be
preceded by an address or address range (as explained in the "Viewing
the file" section). A few commands may be followed by arguments, as
explained within each command's documentation.
Starting ed
Starting ed is simple:
% ed filename
- If the file does exist, ed will read the file, and
print the number of characters in it.
- If file does not exist, ed will complain, by saying
"?filename". This is not a problem; when you tell
ed to save the file (using w with no arguments), it will
save it to the filename given (unless you tell it otherwise;
see the "Saving Files" section for details).
- If you start ed without a filename, you will
need to give the save (w) command a file to write to.
Moving around in ed
Instead of showing you an entire screen of text, ed only
keeps track of a line at a time. At any time, you are on a specific
line, designated by "." (period). The last line of the
file is indicated by the "$" (dollar-sign). To see the
current line number, enter the command n. This will output
the line number, followed by a tab, followed by the contents of the
line.
When you start ed, you begin at the last line. To move to
a different line, simply type the line number (to move to the top of
the file, for example, type 1). When you move to a line,
ed echoes the contents of the line.
You can also enter relative line numbers. For example, -2
will go back two lines, and +5 will go forward five. This
also works with the "." and "$" special lines; for example,
$-1 will give you the second-to-last line, and
.+3 will jump forward three lines (which is the same as the
+3 command).
Pressing <Enter> makes ed go to the next line and
print it. If there is no next line (i.e., you're at the end of the
file), ed gives you its error message, "?".
"Viewing the File" gives you more ways to look at the file.
Viewing the File
To print the current line, use the command p.
To print several lines, prefix p with the start and end
line numbers separated by a , (comma). For example, to
list lines 10 to 20 of a file, use the command 10,20p . In
addition to displaying lines 10 through 20 (inclusive), this sets the
current line number to the last line displayed (20, in this case).
The special characters (. and $) also work with p (and any
other command). In addition, there are two other special characters
that should be introduced: , (comma) and ;
(semicolon). The comma is equivalent to the address pair
"1,$" (i.e., the entire file), and the semicolon is
equivalent to ".,$" (i.e., from the current line to the end
of the file). For example, ",p" prints the entire file,
while ";p" prints the contents of the file from the current
line to the end.
To view whitespace characters, use l (L, not 1). Note that
the end-of-line will be denoted by a "$" symbol, and
various characters (most notably the backslash (\) and the tab, but
there are others; consult the man page for details) will be printed as
their escaped forms (\\ and \t, respectively).
Editing
Note: many of the commands accept an arbitrary number of lines of
text. After entering such a command, you may type in as many lines of
text as you want. Note that there will be no prompt. To signify that
you are done entering text, you must input a line that has only a
single . (period) or a single <Ctrl>-d.
- a
Appends text after the current line (by default). To specify the
place to append text, specify a line number (i.e., 2a will
append text between the 2nd and 3rd lines of the file; $a
will append text to the end of the file). Zero is an allowed address
for this command (unlike most other commands), it indicates that the
text will be placed at the beginning of the file. End with "." or
<Ctrl>-d.
- c
Changes line(s) of text in place. This command requires the
address(es) of the line(s) to be replaced. Note that the lines
specified will be deleted, and the new text inserted where they used
to be. End with "." or <Ctrl>-d.
- d
Deletes line(s) of text. This command requires the address(es) of the
line(s) to be deleted.
- e filename
Deletes the buffer, and replaces it with the file given. The current
line is set to the last line of the buffer. The number of bytes read
is printed.
Note: if the buffer has not been saved, this command will output the
error message. The E command, or the e command
again, will force the loading of the given file, killing any unsaved
changes.
- i
Inserts text before the current line, by default. Like append, except
it inserts before the given line, not after. End with "." or
<Ctrl>-d.
- s/old/new
Substitutes old with new. As given, ed
replaces the first occurrence of old on the current line
with new. The string old can contain regular
expressions, using the same syntax as grep
Putting a trailing g at the end of the substitution (i.e.
s/old/new/g) will change every
occurrence of the pattern on the line.
The s// command can be prefixed with a range. For example,
2,5s/old/new will perform
s/old/new on lines 2 through 5 -- note that
it still only changes the first occurrence on each line.
Putting it all together, we see that the command
,s/old/new/g will replace all
occurrences of old with new in the entire file (the
"," preceding the s// indicates that is should look at all
lines; the /g means that all occurrences on all lines looked
at).
Caution: Using the s// to match or insert a &,
%, \, or \digit (i.e., \0 -
\9), is more involved. Consult the ed man page
for details as to which characters should be escaped and how.
- u
"undo": cancels the effect of the previous command. Note that the
undo command only undoes things that actually changed the buffer, not
commands that only looked at it (i.e., ",l" will be ignored
by the u command, as will any command that does not alter
the contents of the buffer).
Saving
To save, use the w command. If you haven't already
specified a filename (either on the command line or from a previous
save), ed will print its error message (?),
and do nothing. In this case (or if you want to save the file under a
different name), specify the name of the file to save using the
command w filename
After saving, the number of bytes in the file is printed.
Quitting
- Use q to quit only if the file has saved.
- Use Q to quit, whether the file is saved or not.
Note: the q command twice in a row will quit whether or not
the file has been saved.
Helpful (?) Hints
ed is very user-unfriendly. However, these tips may help
you in your editing:
-
ed's only error message is "?". If you give it
a command with an argument that it doesn't recognize, it will give you
the error message "? argument".
-
Needless to say, ed's error messages are not very helpful. The
command h will tell you the reason for ed's most recent
"?" output.
-
The H command makes ed toggle the "Help Mode".
By default, it is off. When turned on, it explains the reason behind
each ?.
-
From the man page:
Some size limitations are in effect: 512 characters in a line, 256
characters in a global command list, and 255 characters in the path
name of a file (counting slashes). The limit on the number of lines
depends on the amount of user memory; each line takes 1 word.
-
ed has even more commands than those listed here. Most of
them are fairly esoteric; frankly, if you need to use them, you should
probably be using a different editor (vi or emacs). However,
ed's man page has reasonably good documentation if you
insist on using it for more complicated tasks; consult it for details.
Ed, the greatest
WYGIWYG editor of all.
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