The vi/ex Editor, Part 1: Vi Editor Fundamentals
Why Vi?
A Heartwarming Edit
The Plan Of This Ongoing Tutorial
The Editor's Basic Concepts
Search Patterns
Searching From Where You Are Now
The Find-Them-All Search
Simple Search Patterns
Metacharacters
Table Of Search Pattern Metacharacters
Character Classes.
What's Coming For The Next Installment.
Why Vi?
A HEARTWARMING EDIT. Pity poor Hal, a corporate maintenance
programmer. A large module of badly-broken, poorly-patched legacy
code -- the spaghetti variety -- finally broke down completely
yesterday, leaving one corporate division running at half speed.
By dint of some inspired fixes during an all-nighter, Hal has the
module up and running again this morning... but just as he's ready
to go out for food that isn't from a vending machine, in walks the
corporation's VP of IS, with a big surprise.
"Nice work on that crash fix, Hal; but right now I need some
formatted technical data about it, in a hurry. The Board of
Directors' Information Systems Committee has called a rush
meeting this morning to convince themselves they're on top of
the problem. I'll be in the hotseat, and I need technical data
I can put up on the video projector to keep them occupied.
"They'll want me to discuss the logfile of errors that led up to
the crash . . . yes, I know that's in /oltp/err/m7, but
appending puts the latest report lines at the bottom of the
file. Those suits aren't interested in what they think is
ancient history, and they wouldn't be caught reading anything
but a commuter train timetable from the bottom up, so you'll
have to make a copy with the order of the lines reversed: what
was the last line becomes the first line, what was the second to
the last line is now line number two, and so on.
"And let's take a look at that logfile.
374a12 44872 130295/074457 nonabort
5982d34 971 130295/221938 nonabort
853f7 2184 140295/102309 abort
...
Hmmm. Explaining the second column to them would be advertising
the fact that we knew this failure was just waiting for a chance
to happen. So while you're at it, go through and erase all but
the first and last digits of each number in column two.
"Oh, and when they get tired of that they'll want to scrutinize
the Lint report. Last month I told them that our Lint
substitute was the greatest thing since Marilyn Monroe, so now
they'll want me to tell them why the messages it still generates
on this module aren't real hazards. Just run Lint over the
revamped module; then combine the Lint output with a copy of the
source file by taking each message line like:
Line 257: obsolete operator +=
and putting the significant part at the end of the source line
it refers to. And put a separator, like XXX, between the source
line and the message so I can page through quickly. Nothing like
a hefty dose of source code they can't begin to fathom to make
the meeting break up early.
"And get right on this. The meeting starts in 35 minutes."
Our VP walks away inwardly smiling, thinking he's getting out of
detailed explanations and putting all the blame on an underling,
just by demanding more editing than anyone could do in the time
available. "I'll tell the Information Systems Committee that I
made it perfectly clear to the programmer that we needed this at
9:30, but when I asked him for it a minute ago he said it wasn't
finished and he wasn't sure when it would be. Then I'll remark
that those programmers just can't understand that keeping
management informed is every bit as important as writing code!"
But Hal has a secret weapon against this squeeze play: an expert
knowledge of the Vi editor.
Reversing the order of the lines in a file is a piece of cake with
this editor. The eight keystrokes in:
:g/^/m0(ret)
will do it. Taking the digits out of the middle of the second
column throughout the file also requires just one command line:
:%s/^\([^ ]* [0-9]\)[0-9]*\([0-9] \)/\1\2(ret)
And integrating the Lint messages into a copy of the source code?
Even that can be automated with the Vi editor. The editor
command:
:%s/Line \([0-9][0-9]*\): \(.*\)/\1s;$; XXX \2(ret)
will turn that file of Lint messages into an editor script, and
running that script on a copy of the source file will mark it up
as requested.
Rather than being portrayed as a bungler, Hal can have it all
ready in a couple of minutes, just by typing a few lines. He'll
even have time to guard against vice-presidential prevarication,
by disappearing into the coffee shop across the street and
reappearing just as the meeting is getting started, to tell the VP
(and everyone else in earshot), "Those files you wanted are in
slash-temp-slash-hal".
THE PLAN OF THIS ONGOING TUTORIAL. I'm writing here for editor
users who have some fluency in Vi/Ex at the surface level. That
is, you know how to do the ordinary things that are belabored in
all the "Introducing Vi" books on the market, but rarely venture
beyond that level.
This tutorial series will explore a lot of other capabilities that
hardly anyone knows are in Vi/Ex. That includes quite a few
tricks that may be built on editor functions we all use every day,
but which nonetheless are not obvious--for instance, telling the
global command to mark every line it encounters. I'll also be
clarifying the real nature of the many misunderstood aspects of
this editor.
To do all this, I'll be explaining things in more depth than you
might think warranted at first. I'll also throw in examples
wherever they seem helpful. And to save you readers from gross
information overload, I'll write this tutorial in a large number
of fairly small modules, to be put up on our website at a calm,
reasonable pace.
The Editor's Basic Concepts
To get a real grasp on this editor's power, you need to know the
basic ideas embodied in it, and a few fundamental building blocks
that are used throughout its many functions.
One cause of editor misuse is that most users, even experienced
ones, don't really know what the editor is good at and what it's
not capable of. Here's a quick rundown on its capabilities.
First, it's strictly a general-purpose editor. It doesn't format
the text; it doesn't have the handholding of a word processor; it
doesn't have built-in special facilities for editing binaries,
graphics, tables, outlines, or any programming language except
Lisp.
It's two editors in one. Visual mode is a better full-screen
editor than most, and it runs faster than those rivals that have a
larger bag of screen-editing commands. Line editing mode dwarfs
the "global search and replace" facilities found in word
processors and simple screen editors; its only rivals are
non-visual editors like Sed where you must know in advance exactly
what you want to do. But in the Vi/Ex editor, the two sides are
very closely linked, giving the editor a combination punch that no
other editor I've tried can rival.
Finally, this editor is at its best when used by people who have
taken the trouble to learn it thoroughly. It's too capable to be
learned well in an hour or two, and too idiosyncratic to be
mastered in a week, and yet the power really is in it, for the few
who care to delve into it. A large part of that power requires
custom-programming the editor: that's not easy or straightforward,
but what can be done by the skillful user goes beyond the direct
programmability of any editor except (possibly) Emacs.
Search Patterns
In quite a few functions of this editor, you can use
string-pattern searching to say where something is to be done or
how far some effect is to extend. These search patterns are a
good example of an editor function that is very much in the Unix
style, but not exactly the same in detail as search patterns in
any other Unix utility.
Search patterns function in both line editing and visual editing
modes, and the work the same way in both, with just a few
exceptions. But how you tell the editor you're typing in a search
pattern will vary with the circumstances.
SEARCHING FROM WHERE YOU ARE NOW. The more common use for search
patterns is to go to some new place in the file, or make some
editing change that will extend from your present position to the
place the pattern search finds. (In line editing mode it's also
possible to have an action take place from one pattern's location
to where another pattern is found, but both searches still start
from your present location.)
If you want to search forward in the file from your present
location (toward the end of the file), precede the search pattern
with a slash (/) character, and type another to end the pattern.
So if you want to move forward to the next instance of the string
"j++" in your file, typing:
/j++/(ret)
will do it. And so will:
/j++(ret)
When there is nothing between the pattern and the RETURN key, the
RETURN itself will indicate the end of the search pattern, so the
second slash is not necessary. And if you are in visual mode, the
ESCAPE key works as well as RETURN does for ending search input,
so
/j++(esc)
is yet another way to make the same request from visual mode.
To search backward (toward the start of the file), begin and end
with a question mark instead of a slash. The same rules of
abbreviation apply to backward searches, so
?j++?(ret)
?j++(ret)
?j++(esc)
are all ways to head backward in the file to the same pattern.
Either way, you've expressed both your request for a pattern
search and the direction the search is to take in just one
keystroke. But don't assume that if you search backward, any
matching pattern the editor finds will be above your present
position in the file, and vice versa if you search forward. The
editor looks there first, certainly, but if it gets to the top or
bottom line of the file and hasn't found a match yet, it wraps
around to the other end of the file and continues the search in
the same direction. That is, if you used a question mark to order
a backward search and the editor searches all the way through the
top line of the file without finding a match, it will go on to
search the bottom line next, then the second-to-the-bottom line,
and so on until (if necessary) it gets back to the point where the
search started. Or if you were searching forward and the editor
found no match up through the very last line of the file, it would
next search the first line, then the second line, etcetera.
If you don't want searches to go past either end of the file,
you'll need to type in a line mode command:
:set nowrapscan(ret)
This will disable the wraparound searching during the present
session in the editor. If you want to restore the wraparound
searching mechanism before you leave the editor, typing
:set wrapscan(ret)
will do it, and you can turn this on and off as often as you like.
THE FIND-THEM-ALL SEARCH. Up to now, I've been considering
searches that find just one instance of the pattern; the one
closest to your current location in the file, in the direction you
chose for the search. But there is another style of search, used
primarily by certain line editing mode commands, such as global
and substitute. This search finds every line in the file (or in a
selected part of the file) that contains the pattern and operates
on them all.
Don't get confused when using the global and substitute commands.
You'll often use both styles of search pattern in one command
line. But the find-one-instance pattern or patterns will go
before the command name or abbreviation, while the find-them-all
pattern will come just behind it. For example, in the command:
:?Chapter 10?,/The End/substitute/cat/dog/g(ret)
the first two patterns refer to the preceding line closest to the
current line that contains the string "Chapter 10" and the closest
following line containing the string "The End". Note that each
address finds only one line. Combined with the intervening comma,
they indicate that the substitute command is to operate on those
two lines and all the lines in between them. But the patterns
immediately after the substitute command itself tell the command
to find every instance of the string "cat" withing that range of
lines and replace it with the string "dog".
Aside from the difference in meaning, the two styles also have
different standards for the delimiters that mark pattern
beginnings and (sometimes) endings. With a find-them-all pattern,
there's no need to indicate whether to search forward or backward.
Thus, you aren't limited to slash and question mark as your
pattern delimiters. Almost any punctuation mark will do, because
the editor takes note of the first punctuation mark to appear
after the command name, and regards it as the delimiter in that
instance. So
:?Chapter 10?,/The End/substitute;cat;dog;g(ret)
:?Chapter 10?,/The End/substitute+cat+dog+g(ret)
:?Chapter 10?,/The End/substitute{cat{dog{g(ret)
are all equivalent to the substitution command above. (It is a
good idea to avoid using punctuation characters that might have a
meaning in the command, such as an exclamation point, which often
appears as a switch at the end of a command name.)
The benefit of this liberty comes when the slash mark will appear
as itself in the search pattern. For example, suppose our
substitution command above was to find each pair of consecutive
slash marks in the text, and separate them with a hyphen--that is,
change // to /-/. Obviously,
:?Chapter 10?,/The End/substitute/////-//g(ret)
won't work; the command will only regard the first three slashes
as delimiters, and everything after that as extraneous characters
at the end of the command. This can be solved by backslashing:
:?Chapter 10?,/The End/substitute/\/\//\/-\//g(ret)
but this is even harder to type correctly than the first attempt
was. But with another punctuation mark as the separator
:?Chapter 10?,/The End/substitute;//;/-/;g(ret)
the typing is easy and the final command is readable.
SIMPLE SEARCH PATTERNS. The simplest search pattern is just a
string of characters you want the editor to find, exactly as
you've typed them in. For instance: "the cat". But, already there
are several caveats:
1. This search finds a string of characters, which may or may
not be words by themselves. That is, it may find its target in
the middle of the phrase "we fed the cat boiled chicken", or in
the middle of "we sailed a lithe catamaran down the coast". It's
all a matter of which it encounters first.
2. Whether the search calls "The Cat" a match or not depends on how
you've set an editor variable named ignorecase. If you've left
that variable in its default setting, the capitalized version will
not match. If you want a capital letter to match its lower-case
equivalent, and vice versa, type in the line mode command
:set ignorecase(ret)
To resume letting caps match only caps and vice versa, type
:set noignorecase(ret)
3. The search absolutely will not find a match where "the"
occurs at the end of one line and "cat" is at the start of the
next line:
and with Michael's careful help, we prodded the cat back into
its cage. Next afternoon several
It makes no difference whether there is or isn't a space
character between one of the words and the linebreak. Finding a
pattern that may break across a line ending is a practically
impossible task with this line-oriented editor.
4. Where the search starts depends on which editor mode you're
using. A search in visual mode starts with the character next to
the cursor. In line mode, the search starts with the line
adjacent to the current line.
METACHARACTERS. Then there are search metacharacters or "wild
cards": characters that represent something other than themselves
in the search. As an example, the metacharacters . and * in
/Then .ed paid me $50*!/(ret)
could cause the pattern to match any of:
Then Ted paid me $5!
Then Red paid me $5000!
Then Ned paid me $50!
or a myriad of other strings. Metacharacters are what give search
patterns their real power, but they need to be well understood.
To understand these, you must know the varied uses of the
backslash (\) metacharacter in turning the "wild card" value of
metacharacters on and off.
In many cases, the meta value of the metacharacter is on whenever
the character appears in a search pattern unless it is preceded by
a backslash; when the backslash is ahead of it the meta value is
turned off and the character simply represents itself. As an
example, the backslash is a metacharacter by itself, even if it
precedes a character that never has a meta value. The only way to
put an actual backslash in your search pattern is to precede it
with another backslash to remove its meta value. That is, to
search for the pattern "a\b", type
/a\\b/(ret)
as your search pattern. If you type
/a\b/(ret)
the backslash will be interpreted as a metacharacter without any
effect (since the letter b is never a metacharacter) and your
search pattern will find the string "ab".
Less-often-used metacharacters are used in exactly the opposite
way. This sort of character represents only itself when it
appears by itself. You must use a preceding backslash to turn the
meta value on. For example, in
/\<cat/
the left angle bracket (<) is a metacharacter; in
/<cat/
it only represents itself. These special metacharacters are
pointed out in the list below.
Finally there is a third class, the most difficult to keep track
of. Usually these metacharacters have their meta values on in
search patterns, and must be backslashed to make them represent
just themselves: like our first example, the backslash character
itself. But if you've changed the default value of an editor
variable named magic to turn it off, they work oppositely--you
then must backslash them to turn their meta value on: like our
second example, the left angle bracket. (Not that you are are
likely to have any reason to turn magic off.) These oddities are
also noted in the list below.
And don't forget the punctuation character that starts and ends
your search pattern, whether it is slash or question mark or
something else. Whatever it is, if it is also to appear as a
character in the pattern you are searching for, you'll have to
backslash it there to prevent the editor thinking it is the end of
the pattern.
TABLE OF SEARCH PATTERN METACHARACTERS
.
A period in a search pattern matches any single character, whether
a letter of the alphabet (upper or lower case), a digit, a
punctuation mark, in fact, any ASCII character except the newline.
So to find "default value" when it might be spelled
"default-value" or "default/value" or "default_value", etcetera,
use /default.value/ as your search pattern. When the editor
variable magic is turned off, you must backslash the period to
give it its meta value.
*
An asterisk, plus the character that precedes it, match any length
string (even zero length) of the character that precedes the
asterisk. So the search string /ab*c/ would match "ac" or "abc"
or "abbc" or "abbbc", and so on. (To find a string with at least
one "b" in it, use /abb*c/ as your search string.) When the
asterisk follows another metacharacter, the two match any length
string of characters that the metacharacter matches. That means
that /a.*b/ will find "a" followed by "b" with anything (or
nothing) between them. When the editor variable magic is turned
off, you must backslash the asterisk to give it its meta value.
^
A circumflex as the first character in a search pattern means that
a match will be found only if the matching string occurs at the
start of a line of text. It doesn't represent any character at
the start of the line, of course, and a circumflex anywhere in a
search pattern except as the first character will have no meta
value. So /^cat/ will find "cat", but only at the start of a
line, while /cat^/ will find "cat^" anywhere in a line.
$
A dollar sign as the last character in a search pattern means the
match must occur at the end of a line of text. Otherwise it's the
same as circumflex, above.
\<
At the start of a search pattern, a backslashed left angle bracket
means the match can only occur at the start of a simple word; at
any other position in a search pattern it is not a metacharacter.
(In this editor, a "simple" word is either a string of one or more
alphanumeric character(s) or a string of one or more
non-alphanumeric, non-whitespace character(s), so "shouldn't"
contains three simple words.) Thus /\<cat/ will find the last
three characters in "the cat" or in "tom-cat", but not in
"tomcat". To remove the meta value from the left angle bracket,
remove the preceding backslash: /<cat/ will find "<cat" regardless
of what precedes it.
\>
At the end of a search pattern, a backslashed right angle bracket
means the match can occur only at the end of a simple word.
Otherwise the same as the left angle bracket, above.
~
The tilde represents the last string you put into a line by means
of a line mode substitute command, regardless of whether you were
in line mode then or ran it from visual mode by preceding it with
a colon (":"). For instance, if your last line mode substitution
command was s/dog/cat/ then a /the ~/ search pattern will find
"the cat". But the input string of a substitute command can use
metacharacters of its own, and if your last use involved any of
those metacharacters then a tilde in your search pattern will give
you either an error message or a match that is not what you
expected. When the editor variable magic is turned off, you must
backslash the tilde to give it its meta value.
CHARACTER CLASSES. There is one metastring form (a "multicharacter
metacharacter") used in search patterns. When several characters
are enclosed within a set of brackets ([]), the group matches any
one of the characters inside the brackets. That is, /part [123]/
will match "part 1", "part 2" or "part 3", whichever the search
comes to first. One frequent use for this feature is in finding a
string that may or may not be capitalized, when the editor
variable ignorecase is turned off (as it is by default). Typing
/[Cc]at/ will find either "Cat" or "cat", and /[Cc][Aa][Tt]/ will
find those or "CAT". (In case there was a slip of the shift key
when "CAT" was typed in, the last pattern will even find "CaT",
"CAt", etcetera.)
There's more power (and some complication) in another feature of
this metastring: there can be metacharacters inside it. Inside the
brackets, a circumflex as the first character reverses the
meaning. Now the metastring matches any one character that is NOT
within the brackets. A /^[^ ]/ search pattern finds a line that
does not begin with a space character. (You're so right if you
think that the different meta values of the circumflex inside and
outside the character class brackets is not one of the editor's
best points.) A circumflex that is not the first character inside
the brackets represents just an actual circumflex.
A hyphen can be a metacharacter within the brackets, too. When
it's between two characters, and the first of the two other
characters has a lower ASCII value than the second, it's as if
you'd typed in all of the characters in the ASCII collating
sequence from the first to the second one, inclusive. So /[0-9]%/
will find any numeral followed by the percent sign (%), just as
/[0123456789]%/ would. A /[a-z]/ search pattern will match any
lower-case letter, and /[a-zA-Z]/ matches any letter, capital or
lower case. These two internal metacharacters can be combined:
/[^A-Z]/ will find any character except a capital letter. A
hyphen that is either the first or the last character inside the
brackets has no meta value. When a character-hyphen-character
string has a first character with a higher ASCII value than the
last character, the hyphen and the two characters that surround it
are all ignored by the pattern search, so /[ABz-a]/ is the same as
/[AB]/.
Backslashing character classes is complex. Within the brackets
you must backslash a right bracket that's part of the class;
otherwise the editor will mistake it for the bracket that closes
the class. Of course you must backslash a backslash that you want
to be part of the class, and you can backslash a circumflex at the
start or a hyphen between two characters if you want them in the
class literally and don't want to move them elsewhere in the
construct. Elsewhere in a search pattern you will have to
backslash a left bracket that you want to appear as itself, or
else the editor will take it as your attempt to begin a character
class. Finally, if magic is turned off, you'll have to backslash
a left bracket when you do want it to begin a character class.
Coming Up Next
In the second part of this tutorial, I'll be following up on all
this information about search patterns, by showing the right ways
to combine them with other elements to generate command addresses.
As a second part finale, I'll show how to tap the enormous power
of the command that looks like an address: the global command.
(DIR) Part 2: Line-Mode Addresses
(DIR) Back to the index