u2

unix v7是最后一个广泛发布的研究型UNIX版本

.SH
II.  DAY-TO-DAY USE
.SH
Creating Files \(em The Editor
.PP
If you have to type a paper or a letter or a program,
how do you get the information stored in the machine?
Most of these tasks are done with
the
.UC UNIX
``text editor''
.UL ed .
Since
.UL ed
is thoroughly documented in 
.UL ed (1) 
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 
called
.UL junk
with some text in it, do the following:
.P1
.ta .65i
ed junk	\fR(invokes the text editor)\f3
a	\fR(command to ``ed'', to add text)\f3
.ft I
now type in
whatever text you want ...
.ft 3
\&.	\fR(signals the end of adding text)\f3
.P2
The ``\f3.\fR'' that signals the end of adding text must be
at the beginning of a line by itself.
Don't forget it,
for until it is typed,
no other
.UL ed
commands will be recognized \(em
everything you type will be treated as text to be added.
.PP
At this point you can do various editing operations
on the text you typed in, such as correcting spelling mistakes,
rearranging paragraphs and the like.
Finally, you must write the information you have typed
into a file with the editor command
.UL w :
.P1
w
.P2
.UL ed
will respond with the number of characters it wrote
into the file 
.UL junk .
.PP
Until the
.UL w
command,
nothing is stored permanently,
so if you hang up and go home
the information is lost.\(dg
.FS
\(dg This is not strictly true \(em
if you hang up while editing, the data you were
working on is saved in a file called
.UL ed.hup ,
which you can continue with at your next session.
.FE
But after
.UL w
the information is there permanently;
you can re-access it any time by typing
.P1
ed junk
.P2
Type a
.UL q
command
to quit the editor.
(If you try to quit without writing,
.UL ed
will print a
.UL ?
to remind you.
A second
.UL q
gets you out regardless.)
.PP
Now create a second file called 
.UL temp
in the same manner.
You should now have two files,
.UL junk
and
.UL temp .
.SH
What files are out there?
.PP
The
.UL ls
(for ``list'') command lists the names
(not contents)
of any of the files that
.UC UNIX
knows about.
If you type
.P1
ls
.P2
the response will be
.P1
junk
temp
.P2
which are indeed the two files just created.
The names are sorted into alphabetical order automatically,
but other variations are possible.
For example,
the command
.P1
ls -t
.P2
causes the files to be listed in the order in which they were last changed,
most recent first.
The
.UL \-l
option gives a ``long'' listing:
.P1
ls -l
.P2
will produce something like
.P1
-rw-rw-rw-  1 bwk   41 Jul 22 2:56 junk
-rw-rw-rw-  1 bwk   78 Jul 22 2:57 temp
.P2
The date and time are of the last change to the file.
The 41 and 78 are the number of characters
(which should agree with the numbers you got from
.UL ed ).
.UL bwk
is the owner of the file, that is, the person
who created it.
The
.UL \-rw\-rw\-rw\- 
tells who has permission to read and write the file,
in this case everyone.
.PP
Options can be combined:
.UL ls\ \-lt
gives the same thing as
.UL ls\ \-l ,
but sorted into time order.
You can also name the files you're interested in,
and 
.UL ls
will list the information about them only.
More details can be found in 
.UL ls (1).
.PP
The use of optional arguments that begin with a minus sign,
like
.UL \-t
and
.UL \-lt ,
is a common convention for
.UC UNIX
programs.
In general, if a program accepts such optional arguments,
they precede any filename arguments.
It is also vital that you separate the various arguments with spaces:
.UL ls\-l
is not the same as
.UL ls\ \ \-l .
.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
.P1
ed junk
1,$p
.P2
.UL ed
will reply with the count of the characters in 
.UL 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
.UL ed
can handle
(several thousand 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
.UL cat ,
the simplest of all the printing programs.
.UL cat
simply prints on the terminal the contents of all the files
named in a list.
Thus
.P1
cat junk
.P2
prints one file, and
.P1
cat junk temp
.P2
prints two.
The files are simply concatenated (hence the name
.UL cat '') ``
onto the terminal.
.PP
.UL pr
produces formatted printouts of files.
As with 
.UL cat ,
.UL pr
prints all the files named 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,
.P1
pr junk temp
.P2
will print
.UL junk
neatly,
then skip to the top of a new page and print
.UL temp
neatly.
.PP
.UL pr
can also produce multi-column output:
.P1
pr -3 junk 
.P2
prints
.UL junk
in 3-column format.
You can use any reasonable number in place of ``3''
and 
.UL pr
will do its best.
.UL pr
has other capabilities as well;
see
.UL pr (1).
.PP
It should be noted that
.UL pr
is
.ul
not
a formatting program in the sense of shuffling lines around
and justifying margins.
The true formatters are
.UL nroff
and
.UL 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
.UL opr
and
.UL lpr .
Which to use depends on
what equipment is attached to 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 it a new name),
like this:
.P1
mv junk precious
.P2
This means that what used to be ``junk'' is now ``precious''.
If you do an
.UL ls
command now,
you will get
.P1
precious
temp
.P2
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 
.UL cp
command:
.P1
cp precious temp1
.P2
makes a duplicate copy of 
.UL precious
in
.UL temp1 .
.PP
Finally, when you get tired of creating and moving
files,
there is a command to remove files from the file system,
called
.UL rm .
.P1
rm temp temp1
.P2
will remove both of the files named.
.PP
You will get a warning message if one of the named files wasn't there,
but otherwise
.UL rm ,
like most
.UC UNIX
commands,
does its work silently.
There is no prompting or chatter,
and error messages are occasionally curt.
This terseness is sometimes disconcerting
to new\%comers,
but experienced users find it desirable.
.SH
What's in a Filename
.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 have already seen, for example,
that in the
.UL ls
command,
.UL ls\ \-t
means to list in time order.
So if you had a file whose name
was
.UL \-t ,
you would have a tough time listing it by name.
Besides the minus sign, there are other characters which
have special meaning.
To avoid pitfalls,
you would do well to 
use only letters, numbers and the period
until you're familiar with the situation.
.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 
.UL ed
will not handle really big files.
Thus you should type the document as a number of files.
You might have a separate file for each chapter,
called
.P1
chap1
chap2
.ft R
etc...
.P2
Or, if each chapter were broken into several files, you might have
.P1
chap1.1
chap1.2
chap1.3
\&...
chap2.1
chap2.2
\&...
.P2
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
.P1
pr chap1.1 chap1.2 chap1.3 ......
.P2
but you would get tired pretty fast, and would probably even make mistakes.
Fortunately, there is a shortcut.
You can say
.P1
pr chap*
.P2
The
.UL *
means ``anything at all,''
so this translates into ``print all files
whose names begin with 
.UL chap '',
listed in alphabetical order.
.PP
This shorthand notation
is not a property of the
.UL pr
command, by the way.
It is system-wide, a service of the program
that interprets commands
(the ``shell,''
.UL sh (1)).
Using that fact, you can see how to list the names of the files in the book:
.P1
ls chap*
.P2
produces
.P1
chap1.1
chap1.2
chap1.3
\&...
.P2
The
.UL *
is not limited to the last position in a filename \(em
it can be anywhere
and can occur several times.
Thus
.P1
rm *junk* *temp*
.P2
removes all files that contain
.UL junk
or
.UL temp
as any part of their name.
As a special case,
.UL *
by itself matches every filename,
so
.P1
pr *
.P2
prints all your files
(alphabetical order),
and
.P1
rm *
.P2
removes
.ul
all files.
(You had better be
.IT  very 
sure that's what you wanted to say!)
.PP
The
.UL *
is not 
the only pattern-matching feature available.
Suppose you want to print only chapters 1 through 4 and 9.
Then you can say
.P1
pr chap[12349]*
.P2
The
.UL [...]
means to match any of the characters inside the brackets.
A range of consecutive letters or digits can be abbreviated,
so you can also do this 
with
.P1
pr chap[1-49]*
.P2
Letters can also be used within brackets:
.UL [a\-z]
matches any character in the range
.UL a
through
.UL z .
.PP
The
.UL ?
pattern matches any single character,
so
.P1
ls ?
.P2
lists all files which have single-character names,
and
.P1
ls -l chap?.1
.P2
lists information about the first file of each chapter
.UL chap1.1 \&, (
.UL chap2.1 ,
etc.).
.PP
Of these niceties,
.UL *
is certainly 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
.UL * ,
.UL ? ,
etc.,
enclose the entire argument in single quotes,
as in
.P1
ls \(fm?\(fm
.P2
We'll see some more examples of this shortly.
.SH
What's in a Filename, Continued
.PP
When you first made that file called
.UL junk ,
how did 
the system
know that there wasn't another
.UL junk
somewhere else,
especially since the person in the next office is also
reading this tutorial?
The answer is that generally each user 
has a private
.IT directory ,
which contains only the files that belong to him.
When you log in, you are ``in'' your directory.
Unless you take special action,
when you create a new file,
it is made in the directory that you are currently in;
this is most often your own directory,
and thus the file is unrelated to any other file of the same name
that might exist in someone else's directory.
.PP
The set of all files
is organized into a (usually big) tree,
with your files located several branches into the tree.
It is possible for you to ``walk'' around this tree,
and to find any file in the system, by starting at the root
of the tree and walking along the proper set of branches.
Conversely, you can start where you are and walk toward the root.
.PP
Let's try the latter first.
The basic tools is the command
.UL pwd
(``print working directory''),
which prints the name of the directory you are currently in.
.PP
Although the details will vary according to the system you are on,