u2

UNIX版本6的源代码

.SH
II.  DAY-TO-DAY USE
.SH
Creating Files _ The Editor
.PP
If we have to type a paper or a letter or a program,
how do we get the information stored in the machine?
Most of these tasks are done with
the
.UC UNIX
``text editor''
.C ed .
Since
.C ed
is thoroughly documented in 
.SE ed (I) 
and explained in
.ul
A Tutorial Introduction to the UNIX Text Editor,
we won't spend any time here describing how to use it.
All we want it for right now is to make some
.ul
files.
(A file is just a collection of information stored in the machine,
a simplistic but adequate definition.)
.PP
To create a file with some text in it, do the following:
.B1
 ed	(invokes the text editor)
 a	(command to ``ed'', to add text)
.I
 now type in
 whatever text you want ...
.R
 \fB.\fP	(signals the end of adding text)
.B2
At this point we could do various editing operations
on the text we typed in, such as correcting spelling mistakes,
rearranging paragraphs and the like.
Finally, we write the information we have typed
into a file with the editor command ``w'':
.B1
w junk
.B2
.C ed
will respond with the number of characters it wrote
into the file called ``junk''.
.PP
Suppose we now add a few more lines with ``a'',
terminate them with ``.'',
and write the whole thing out as ``temp'', using
.B1
w temp
.B2
We should now have two files, a smaller one called ``junk'' and a bigger one
(bigger by the extra lines) called ``temp''.
Type a ``q'' to quit the editor.
.SH
What files are out there?
.PP
The
.C ls
(for ``list'') command lists the names
(not contents) of any of the files that
.UC UNIX
knows about.
If we type
.B1
ls
.B2
the response will be
.B1
junk
temp
.B2
which are indeed our two files.
They are sorted into alphabetical order automatically,
but other variations are possible.
For example,
if we add the optional argument ``-t'',
.B1
ls -t
.B2
lists them in the order in which they were last changed,
most recent first.
The ``-l'' option gives a ``long'' listing:
.B1
ls -l
.B2
will produce something like
.B1
-rw-rw-rw-  1 bwk   41 Sep 22 12:56 junk
-rw-rw-rw-  1 bwk   78 Sep 22 12:57 temp
.B2
The date and time are of the last change to the file.
The 41 and 78 are the number of characters
(you got the same thing from
.C ed ).
``bwk'' is the owner of the file _ the person
who created it.
The ``-rw-rw-rw-'' tells who has permission to read and write the file,
in this case everyone.
.PP
Options can be combined:
``ls -lt'' would give the same thing,
but sorted into time order.
You can also name the files you're interested in,
and 
.C ls
will list the information about them only.
More details can be found in  
.SE ls (I).
.PP
It is generally true of
.UC UNIX
programs that ``flag'' arguments like ``-t''
precede filename arguments.
.SH
Printing Files
.PP
Now that you've got a file of text,
how do you print it so people can look at it?
There are a host of programs that do that,
probably more than are needed.
.PP
One simple thing is to use the editor,
since printing is often done just before making changes anyway.
You can say
.B1
ed junk
1,$p
.B2
.C ed
will reply with the count of the characters in ``junk''
and then print all the lines in the file.
After you learn how to use the editor,
you can be selective about the parts you print.
.PP
There are times when it's not feasible to use the editor for printing.
For example, there is a limit on how big a file
.C ed
can handle
(about 65,000 characters or 4000 lines).
Secondly, 
it
will only print one file at a time,
and sometimes you want to print several, one after another.
So here are a couple of alternatives.
.PP
First is
.C cat ,
the simplest of all the printing programs.
.C cat
simply copies all the files in a list onto the terminal.
So you can say
.B1
cat junk
.B2
or, to print two files,
.B1
cat junk temp
.B2
The two files are simply concatenated (hence the name ``cat'')
onto the terminal.
.PP
.C pr
produces formatted printouts of files.
As with 
.C cat ,
.C pr
prints all the files in a list.
The difference is that it produces 
headings with date, time, page number and file name
at the top of each page,
and
extra lines to skip over the fold in the paper.
Thus,
.B1
pr junk temp
.B2
will list ``junk'' neatly,
then skip to the top of a new page and list
``temp'' neatly.
.PP
.C pr
will also produce multi-column output:
.B1
pr -3 junk 
.B2
prints ``junk'' in 3-column format.
You can use any reasonable number in place of ``3''
and 
.C pr
will do its best.
.PP
It should be noted that
.C pr
is
.ul
not
a formatting program in the sense of shuffling lines around
and justifying margins.
The true formatters are
.C roff ,
.C nroff ,
and
.C troff ,
which we will get to in the section on document preparation.
.PP
There are also programs that print files
on a high-speed printer.
Look in your manual under
.C opr
and
.C lpr .
Which to use depends on the hardware configuration
of your machine.
.SH
Shuffling Files About
.PP
Now that you have some files in the file system
and some experience in printing them,
you can try bigger things.
For example,
you can move a file from one place to another
(which amounts to giving a file a new name),
like this:
.B1
mv junk precious
.B2
This means that what used to be ``junk'' is now ``precious''.
If you do an
.C ls
command now,
you will get
.B1
precious
temp
.B2
Beware that if you move a file to another one
that already exists,
the already existing contents are lost forever.
.PP
If you want
to make a
.ul
copy
of a file (that is, to have two versions of something),
you can use the 
.C cp
command:
.B1
cp precious temp1
.B2
makes a duplicate copy of 
``precious''
in
``temp1''.
.PP
Finally, when you get tired of creating and moving
files,
there is a command to remove files from the file system,
called
.C rm .
.B1
rm temp temp1
.B2
will remove all of the files named.
You will get a warning message if one of the named files wasn't there.
.SH
Filename, What's in a
.PP
So far we have used filenames without ever saying what's
a legal name,
so it's time for a couple of rules.
First, filenames are limited to 14 characters,
which is enough to be descriptive.
Second, although you can use almost any character
in a filename,
common sense says you should stick to ones that are visible,
and that you should probably avoid characters that might be used
with other meanings.
We already saw, for example,
that in the
.C ls
command,
``ls -t'' meant to list in time order.
So if you had a file whose name
was ``-t'',
you would have a tough time listing it by name.
There are a number of other characters which
have special meaning either to
.UC UNIX
as a whole or to numerous commands.
To avoid pitfalls,
you would probably do well to 
use only letters, numbers and the period.
(Don't use the period as the first character of a filename,
for reasons too complicated to go into.)
.sp
.PP
On to some more positive suggestions.
Suppose you're typing a large document
like a book.
Logically this divides into many small pieces,
like chapters and perhaps sections.
Physically it must be divided too,
for 
.C ed
will not handle big files.
Thus you should type the document as a number of files.
You might have a separate file for each chapter,
called
.B1
.ne 3
chap1
chap2
etc...
.B2
Or, if each chapter were broken into several files, you might have
.B1
.ne 7
chap1.1
chap1.2
chap1.3
 ...
chap2.1
chap2.2
 ...
.B2
You can now tell at a glance where a particular file fits into the whole.
.PP
There are advantages to a systematic naming convention which are not obvious
to the novice
.UC UNIX 
user.
What if you wanted to print the whole book?
You could say
.B1
pr chap1.1 chap1.2 chap1.3 ......
.B2
but you would get tired pretty fast, and would probably even make mistakes.
Fortunately, there is a shortcut.
You can say
.B1
pr chap*
.B2
The ``*'' means ``anything at all'',
so this translates into ``print all files
whose names begin with `chap' '',
listed in alphabetical order.
This shorthand notation
is not a property of the
.C pr
command, by the way.
It is system-wide, a service of the program
that interprets commands
(the ``shell''
.SE sh (I)).
Using that fact, you can see how to list the files of the book:
.B1
ls chap*
.B2
produces
.B1
.ne 4
chap1.1
chap1.2
chap1.3
 ...
.B2
The ``*'' is not limited to the last position in a filename _
it can be anywhere.
Thus
.B1
rm *junk*
.B2
removes all files that contain ``junk''
as any part of their name.
As a special case, ``*'' by itself matches every filename,
so
.B1
pr *
.B2
prints all the files
(alphabetical order),
and
.B1
rm *
.B2
removes
.ul
all files.
(You had better be sure that's what you wanted to say!)
.PP
The ``*'' is not the only pattern-matching feature available.
Suppose you want to print only chapters 1 through 4 and 9 of the
book.
Then you can say
.B1
pr chap[12349]*
.B2
The ``[...]'' 
means to match any of the characters inside the brackets.
You can also do this 
with
.B1
pr chap[1-49]*
.B2
``[a-z]'' matches any character in the range
.ul
a
through
.ul 
z.
There is also a ``?'' character, which matches any single character,
so
.B1
pr ?
.B2
will print all files which have single-character names.
.PP
Of these niceties,
``*'' is probably the most useful,
and you should get used to it.
The others are frills, but worth knowing.
.PP
If you should ever have to turn off the special meaning
of ``*'', ``?'', etc.,
enclose the entire argument in quotes (single or double),
as in
.B1
ls "?"
.B2