intro

unix v7是最后一个广泛发布的研究型UNIX版本

Also, the command
.IR tabs (1)
will set the tab stops automatically on many terminals.
.LP
.I
How to run a program; the Shell.\ \ 
.R
When you have successfully logged in, a program
called the Shell is listening to your terminal.
The Shell reads typed-in lines, splits them up
into a command name and arguments, and executes the command.
A command is simply an executable program.
The Shell looks first in your current directory
(see below)
for a program with the given name,
and if none is there, then in a system directory.
There is nothing special about system-provided
commands except that they are kept in a directory
where the Shell can find them.
.LP
The command name is always the first word on an input line;
it and its arguments are separated from one another by
spaces.
.LP
When a program terminates, the Shell will ordinarily regain control and type 
a `$' at you to indicate that it is ready for another command.
.LP
The Shell has many other capabilities, which are described in detail in section
.IR sh (1).
.LP
.I
The current directory.\ \ 
.R
.UX
has a file system arranged in a hierarchy of directories.
When the system administrator gave you a user name,
he also created a directory for you (ordinarily
with the same name as your user name).
When you log in, any file
name you type is by default
in this directory.
Since you are the owner of this directory, you have
full permission to read, write, alter, or destroy
its contents.
Permissions to have your will with other directories
and files will have been granted or denied to you
by their owners.
As a matter of observed fact, few
.UX
users
protect their files from destruction,
let alone perusal, by other users.
.LP
To change the
current directory (but not the set of permissions you
were endowed with at login) use
.IR cd (1).
.LP
.I
Path names.\ \ 
.R
To refer to files not in the current directory, you must
use a path name.
Full path names begin with `/', the name of the root directory of the
whole file system.
After the slash comes the name of each directory containing the next
sub-directory (followed by a `/') until finally the
file name is reached.
For example,
.I
/\^usr/\^lem/\^filex
.R
refers to the file
.I
filex
.R
in the directory
.I
lem; lem
.R
is itself a subdirectory of
.I
usr; usr
.R
springs directly from the root directory.
.LP
If your current directory has subdirectories,
the path names of files therein begin with
the name of the subdirectory with no prefixed `/'.
.LP
A path name may be used anywhere a file name is
required.
.LP
Important commands which modify the contents of files
are
.IR cp (1),
.IR mv (1),
and
.IR rm (1),
which respectively copy, move (i.e. rename) and remove files.
To find out the status of files or directories, use 
.IR ls (1).
See
.IR mkdir (1)
for making directories and
.I
rmdir
.R
(in
.IR rm (1))
for destroying them.
.LP
For a fuller discussion of the file system, see
`The
.UX
Time-Sharing System,'
by Ken Thompson and Dennis Ritchie.
It may also be useful to glance through
section 2 of this manual, which discusses
system calls, even if you don't intend
to deal with the system at that level.
.LP
.I
Writing a program.\ \ 
.R
To enter the text of a source program into a
.UX
file, use
the editor
.IR ed (1).
The three principal languages in
.UX
are
provided by the C compiler
.IR cc (1),
the Fortran compiler
.IR f77 (1),
and the assembler
.IR as (1).
After the program text has been entered through 
the editor
and written on a file, you can give the file
to the appropriate language processor as an argument.
The output of the language processor
will be left on a file in the current directory named `a.out'.
(If the output is precious, use
.I mv
to move it to a less
exposed name soon.)\ 
If you wrote in assembly language, you will probably
need to load the program with library subroutines; see
.IR ld (1).
The other two language processors call
the loader automatically.
.LP
When you have finally gone through this entire process
without provoking any diagnostics, the resulting program
can be run by giving its name to the Shell
in response to the `$' prompt.
.LP
Your programs can receive arguments from the command line
just as system programs do,
see
.IR exec (2).
.LP
.I
Text processing.\ \ 
.R
Almost all text is entered through the editor
.IR ed (1).
The commands most often used to write text on a terminal are:
.I
cat, pr, roff
.R
and
.I nroff,
all in section 1.
.LP
The
.I cat
command simply dumps \s8ASCII\s10 text
on the terminal, with no processing at all.
The
.IR pr ""
command paginates the text, supplies headings,
and has a facility for multi-column output.
.I
Nroff
.R
is an elaborate text formatting program.
Used naked, it requires careful forethought, but for
ordinary documents it has been tamed;
see
.IR ms (7).
.I Roff
is a simpler text formatting
program, and requires somewhat less forethought.
.I
.LP
.I Troff
prepares documents for a
Graphics Systems phototypesetter;
it is very similar to 
.I nroff,
and often works from exactly the same
source text.
It was used to produce this manual.
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.I
Status inquiries.\ \ 
.R
Various commands exist to provide you with useful
information.
.IR Who (1)
prints a list of users presently logged in.
.IR Date (1)
prints the current time and date.
.IR Ls (1)
will list the files in your directory or give
summary information about particular files.
.LP
.I
Surprises.\ \ 
.R
Certain commands provide inter-user communication.
Even if you do not plan to use them, it would be
well to learn something about them, because someone else may
aim them at you.
.LP
To communicate with another user currently logged in,
.IR write (1)
is used;
.IR mail (1)
will leave a message whose presence will be announced
to another user when he next logs in.
The write-ups in the manual also suggest how to respond to
the two commands if you are a target.
.LP
When you log in, a message-of-the-day may greet you
before the first `$'.
.SH
CONVERTING FROM THE 6TH EDITION
.LP
There follows a catalogue of significant, mostly incompatible,
changes that will affect old users converting to the 7th edition.
No attempt is made to list all new facilities, or even all
minor, but easily spotted changes,
just the bare essentials without which it will be
almost impossible to do anything.
.LP
.I
Addressing files.\ \ 
.R
Byte addresses in files are now long (32-bit) integers.
Accordingly
.I seek
has been replaced by
.IR lseek (2).
Every program that contains a 
.I seek
must be modified.
.I Stat
and
.IR fstat (2)
have been affected similarly, since file lengths are now
32- rather than 24-bit quantities.
.LP
.I
Assembly language.\ \ 
.R
System entry points are no longer built in symbols.
Their values must be obtained from
.I /usr/include/sys.s,
see
.IR intro (2).
All system calls modify r0.
This means that sequences like
.DS
mov	file,r0
sys	lseek,0,0,2
sys	write,buf,n
.DE
will no longer work.
(In fact, 
.I lseek
now modifies r1 as well, so be doubly cautious.)
.LP
The
.IR sleep (2)
entry point is gone; see the more general facility,
.IR alarm,
plus
.I pause.
.LP
Few library functions have assembly language entry points any more.
You will have to simulate the C calling sequence.
.LP
.I
Stty and gtty.\ \ 
.R
These system calls have been extensively altered,
see
.IR ioctl (2)
and
.IR tty (4).
.LP
.I
Archive files.\ \ 
.R
The format of files produced by
.IR ar (1)
has been altered.
To convert to the new style, use
.IR arcv (1).
.LP
.I 
C language, lint.\ \ 
.R
The official syntax for initialization
requires an equal sign = before an initializer,
and brackets { } around compound initial values;
arrays and structures are now initialized honestly.
Two-address operators, such as =+ and =-, are now written
+= and -= to avoid ambiguities, although the old
style is still accepted.
You will also certainly want to learn about
.DS
long integers
type definitions
casts (for type conversion)
unions (for more honest storage sharing)
#include <filename> (which searches in standard places)
.DE
.LP
The program
.IR lint (1)
checks for obsolete syntax and
does strong type checking of C programs, singly
or in groups that are expected to be loaded together.
It is indispensable for conversion work.
.LP
.I Fortran.\ \ 
The old 
.I fc
is replaced by
.I f77,
a true compiler for Fortran 77,
compatible with C.
There are substantial changes in the language;
see `A Portable Fortran 77 Compiler' in Volume 2.
.LP
.I
Stream editor.\ \ 
.R
The program
.IR sed (1)
is adapted to massive, repetitive
editing jobs of the sort encountered in converting to
the new system.
It is well worth learning.
.LP
.I
Standard I/O.\ \ 
.R
The old 
.I
fopen, getc, putc
.R
complex and the old
.I \-lp
package are both dead,
and even
.I getchar
has changed.
All have been replaced by the clean, highly efficient,
.IR stdio (3)
package.
The first things to know are that
.IR getchar (3)
returns the integer EOF (\-1), which is not a possible byte value,
on end of file, that 518-byte buffers are out, and that there
is a defined FILE data type.
.LP
.I Make.\ \ 
The program
.IR make (1)
handles the recompilation and loading of
software in an orderly way from
a `makefile' recipe given for each piece of software.
It remakes only as much as the modification dates of the input files
show is necessary.
The makefiles will guide you in building your new system.
.LP
.I
Shell, chdir.\ \ 
.R
F. L. Bauer once said Algol 68 is the Everest that
must be climbed by every computer scientist because
it is there.
So it is with the shell for
.UX
users.
Everything beyond simple command invocation from a terminal is
different.
Even
.I chdir
is now spelled
.I cd.
You will want to study
.IR sh (1)
long and hard.
.LP
.I Debugging.\ \ 
.IR Adb (1)
is a far more capable replacement for the debugger
.I db.
The first-time user should be especially careful about
distinguishing / and ? in
.I adb
commands, and watching to make sure that the
.I x
whose value he asked for is the real
.I x,
and not just some absolute location equal to the stack offset
of some automatic
.I x.
You can always use the `true' name,
.I _x,
to pin down a C external variable.
.LP
.I Dsw.
This little-known, but indispensable facility has been
taken over by
.I
rm \-ri.
.LP
.I
Boot procedures.\ \ 
.R
Needless to say, these are all different.
See section 8 of this volume, and
`Setting up \s8UNIX\s10' in Volume 2.