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UNIX v6源代码 这几乎是最经典的unix版本 unix操作系统设计和莱昂氏unix源代码分析都是用的该版

.sp
.SH
III. DOCUMENT PREPARATION
.sp
.PP
.UC UNIX
is extensively used for document preparation.
There are three major 
.ul
formatting
programs,
that is,
programs which produce a text with
justified right margins, automatic page numbering and titling,
automatic hyphenation,
and the like.
The simplest of these formatters is
.C roff ,
which
in fact is simple enough that if you type almost any text
into a file and
``roff'' 
it,
you will get plausibly formatted output.
You can do better with a little knowledge,
but basically it's 
easy to learn and use.
We'll get back to 
.C roff
shortly.
.PP
.C nroff
is similar to
.C roff
but does much less for you automatically.
It will do a great deal more,
once you know how to use it.
.PP
Both
.C roff
and
.C nroff
are designed to produce output on terminals,
line-printers, and the like.
The third formatter,
.C troff
(pronounced ``tee-roff''),
instead drives a Graphic Systems phototypesetter,
which produces very high quality output on photographic paper.
This 
paper
was printed on the phototypesetter by
.C troff .
.if n (Or at least it will be.)
.PP
Because
.C nroff
and
.C troff
are relatively hard to learn to use effectively,
several
``packages'' of canned formatting requests are available
which let you do things
like paragraphs, running titles, multi-column output,
and so on, with little effort.
Regrettably, details vary from system to system.
.SH
ROFF
.PP
The basic idea of
.C roff
(and of
.C nroff
and
.C troff ,
for that matter)
is that the text to be formatted
contains within it ``formatting commands''
that indicate in detail how the formatted text is to look.
For example, there might be commands that specify how long lines are,
whether to use single or double spacing,
and what running titles to use on each page.
In general, you don't have to spell
out all of the possible formatting details.
Most of them have
``default values'',
which you will get if you say nothing at all.
For example,
unless you take special precautions,
you'll get single-spaced output, 65-character lines,
justified right margins, and 58 text lines per page
when you 
.C roff
a file.
This is the reason that
.C roff
is so simple _
most of the decisions have already been made
for you.
.PP
Some things do have to be done, however.
If you want a document
broken into paragraphs, you have to tell
.C roff
where to add the extra blank lines.
This is done with the
``.sp'' command:
.B1
.ne 3
this is the end of one paragraph.
^sp
This begins the next paragraph ...
.B2
In
.C roff
(and in
.C nroff
and
.C troff ),
formatting commands consist of a period followed by two letters,
and they must appear at the beginning of a line, all by themselves.
The ``.sp'' command tells
.C roff
to finish printing any of the previous
line
that might be still unprinted,
then print a blank line before continuing.
You can have more space if you wish;
``.sp 2'' asks for 2 spaces, and so on.
.PP
If you simply want to
ensure that subsequent text appears on a fresh output line,
you can use the command ``.br'' (for ``break'')
instead of ``.sp''.
.PP
Most of the other commonly-used
.C roff
commands are equally simple.
For example you can center one or more lines with the ``.ce'' command.
.B1
.ne 3
^ce
Title of Paper
^sp 2
.B2
causes the title to be centered,
then followed by two blank lines.
As with ``.sp'', ``.ce'' can be followed by a number;
in that case, that many input lines are centered.
.PP
``.ul'' underlines lines, and can also be followed by a number:
.B1
.ne 5
^ce 2
^ul 2
An Earth-shaking Paper
^sp
John Q. Scientist
.B2
will center and underline the two text lines.
Notice that the ``.sp'' between them
is not part of the line count.
.PP
You can get multiple-line spacing instead of the default single-spacing
with the ``.ls'' command:
.B1
^ls 2
.B2
causes double spacing.
.PP
If you're typing things like tables,
you will not want the automatic filling-up and justification
of output lines that is done by default.
You can turn this off with the command
``.nf'' (no-fill),
and then back on again with ``.fi'' (fill).
Thus
.B1
.ne 7
this section is filled by default.
^nf
here lines will appear just
as you typed them _
no extra spaces, no moving of words.
^fi
Now go back to filling up output lines.
.B2
.PP
You can change the line-length with ``.ll'',
and the left margin (the indent) by ``.in''.
These are often used together to make offset blocks of text:
.B1
^ll \-10
^in +10
.fi
.ll -5
this text will be moved 10 spaces to the right
and the lines will also be shortened 10 characters from the right.
The ``+'' and ``\-'' mean to 
.ul
change
the previous value by that much.
Now revert:
.ll +5
.nf
^ll +10
^in \-10
.B2
Notice that ``.ll +10'' adds ten characters to the line length,
while ``.ll 10'' makes the line ten characters
.ul
long.
.PP
The ``.ti'' command
indents (in either direction) just like ``.in'', except for only one line.
Thus to make a new paragraph with a 10-character indent,
you would say
.B1
.ne 3
^sp
^ti +10
New paragraph ...
.B2
.PP
You can put running titles on both top and bottom of each page,
like this:
.B1
.ne 2
^he "left top"center top"right top"
^fo "left bottom"center bottom"right bottom"
.B2
The header or footer is divided into three parts,
which are marked off by any character you like.
(We used a double quote.)
If there's nothing between the markers, that part
of the title will be blank.
If you use a percent sign anywhere in ``.he'' or ``.fo'',
the current page number will be inserted.
So to get centered page numbers with dashes around them,
at the top,
use
.B1
^he ""\- % \-""
.B2
You can skip to the top of a new page at any time
with the ``.bp'' command;
if ``.bp'' is followed by a number,
that will be the new page number.
.PP
The foregoing is probably enough about 
.C roff
for you to go off and format most everyday documents.
Read
.SE roff (I)
for more details.
.SH
Hints for Preparing Documents
.PP
Most documents go through several versions (always more than you expected) before they
are finally finished.
Accordingly, you should do whatever possible to make
the job of changing them easy.
.PP
First, when you do the purely mechanical operations of typing,
type so subsequent editing will be easy.
Start each sentence on a new line.
Make lines short,
and break lines at natural places,
such as after commas and semicolons,
rather than randomly.
Since most people change documents by rewriting phrases
and adding, deleting and rearranging sentences,
these precautions simplify any editing
you have to do later.
.PP
The second aspect of making change easy
is not to commit yourself to formatting details too early.
For example, if you decide that each paragraph is to have
a space and an indent of 10 characters,
you might type, before each,
.B1
.ne 2
^sp
^ti +10
.B2
But what happens when later you decide that it would have
been better to have
no space and an indent of only 5 characters?
It's tedious indeed to go back and patch this up.
.PP
Fortunately, all of the formatters let
you delay decisions until the actual moment of running.
The secret is to define a new operation
(called a
.ul
macro),
for each formatting operation you want to do,
like making a new paragraph.
You can say, in all three formatters,
.B1
.ne 4
^de PP
.ne 2
^sp
^ti +10
^^
.B2
This
.ul
defines
``.PP''
as a new
.C roff
(or
.C nroff 
or
.C troff )
operation,
whose meaning is exactly
.B1
^sp
^ti +10
.B2
(The ``..'' marks the end of the definition.)
Whenever ``.PP'' is encountered in the text,
it is as if you had typed 
the two lines of the definition
in place of it.
.PP
The beauty of this scheme is that now, if you change your mind
about what a paragraph should look like,
you can change the formatted output
merely by changing the definition of
``.PP''
and re-running the formatter.
.PP
As a rule of thumb, for all but the most trivial jobs,
you should type a document in terms of a set of macros
like ``.PP'',
and then define them appropriately.
As long as you have entered the text in some systematic way,
it can always be cleaned up and re-formatted
by a judicious combination of
editing and macro definitions.
The packages of formatting commands
that we mentioned earlier are simply collections
of macros designed for particular formatting tasks.
.PP
One of the main differences between
.C roff
and the other formatters
is that macros in
.C roff
can only be lines of text and formatting commands.
In
.C nroff 
and
.C troff ,
macros may have arguments,
so they can have different effects
depending on how they are called
(in exactly the same way that the ``.sp'' command
has an argument, the number of spaces you want).
.SH
Miscellany
.PP
In addition to the basic formatters,
.UC UNIX
provides
a host of supporting programs.
.C eqn
and
.C neqn
let you integrate mathematics
into the text of a document,
in a language that closely resembles the way
you would speak it aloud.
.C spell
and
.C typo
detect possible spelling mistakes in a document.
.C grep
looks for lines
containing a particular text pattern 
(rather like the editor's context search does,
but on a whole series of files).
For example,
.B1
grep  "ing$"  chap*
.B2
will find all lines ending
in the letters ``ing'' in the series of files ``chap*''.
(It is almost always a good practice to put quotes around
the pattern you're searching for,
in case it contains characters that have a special meaning for the shell.)
.PP
.C wc
counts the words and (optionally) lines in a set of files.
.C tr
translates characters into other characters;
for example it will convert upper to lower case and vice versa.
This translates upper into lower:
.B1
tr  "[A-Z]"  "[a-z]"
.B2
.PP
.C diff
prints a list of the differences between
two files,
so you can compare
two versions of something automatically
(which certainly beats proofreading by hand).
.C sort
sorts files in a variety of ways;
.C cref
makes cross-references;
.C ptx
makes a permuted index
(keyword-in-context listing).
.PP
Most of these programs are either independently documented
(like
.C eqn
and
.C neqn ),
or are sufficiently simple that the description in
the
.ul 2
.UC UNIX
Programmer's Manual
is adequate explanation.