csh.1

早期freebsd实现

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.\"	@(#)csh.1	8.1 (Berkeley) 6/8/93
.\"
.EH 'USD:4-%''An Introduction to the C shell'
.OH 'An Introduction to the C shell''USD:4-%'
.\".RP
.TL
An Introduction to the C shell
.AU
William Joy
(revised for 4.3BSD by Mark Seiden)
.AI
Computer Science Division
.br
Department of Electrical Engineering and Computer Science
.br
University of California, Berkeley
.br
Berkeley, California 94720
.AB
.I Csh
is a new command language interpreter for
.UX
systems.
It incorporates good features of other shells and a
.I history
mechanism similar to the
.I redo
of \s-2INTERLISP\s0.
While incorporating many features of other shells which make
writing shell programs (shell scripts) easier,
most of the features unique to
.I csh
are designed more for the interactive \s-2UNIX\s0 user.
.PP
\s-2UNIX\s0
users who have read a general introduction to the system
will find a valuable basic explanation of the shell here.
Simple terminal interaction with
.I csh
is possible after reading just the first section of this document.
The second section describes the shell's capabilities which you can
explore after you have begun to become acquainted with the shell.
Later sections introduce features which are useful, but not necessary
for all users of the shell.
.PP
Additional information includes an appendix listing special characters of the shell
and a glossary of terms and commands introduced in this manual.
.AE
.SH
.if n .ND
Introduction
.PP
A
.I shell
is a command language interpreter.
.I Csh
is the name of one particular command interpreter on
\s-2UNIX\s0.
The primary purpose of
.I csh
is to translate command lines typed at a terminal into
system actions, such as invocation of other programs.
.I Csh
is a user program just like any you might write.
Hopefully,
.I csh
will be a very useful program for you
in interacting with the \s-2UNIX\s0 system.
.PP
In addition to this document, you will want to refer to a copy
of the \s-2UNIX\s0 User Reference Manual.
The
.I csh
documentation in section 1 of the manual provides a full description of all
features of the shell and is the definitive reference for questions
about the shell.
.PP
Many words in this document are shown in
.I italics.
These are important words;
names of commands, and words which have special meaning in discussing
the shell and \s-2UNIX\s0.
Many of the words are defined in a glossary at the end of this document.
If you don't know what is meant by a word, you should look
for it in the glossary.
.SH
Acknowledgements
.PP
Numerous people have provided good input about previous versions
of 
.I csh
and aided in its debugging and in the debugging of its documentation.
I would especially like to thank Michael Ubell
who made the crucial observation that history commands could be
done well over the word structure of input text, and implemented
a prototype history mechanism in an older version of the shell.
Eric Allman has also provided a large number of useful comments on the
shell, helping to unify those concepts which are present and to identify
and eliminate useless and marginally useful features.
Mike O'Brien suggested the pathname hashing
mechanism which speeds command execution.
Jim Kulp added the job control and directory stack primitives and
added their documentation to this introduction.
.br
.bp
.NH
Terminal usage of the shell
.NH 2
The basic notion of commands
.PP
A
.I shell
in
\s-2UNIX\s0
acts mostly as a medium through which other
.I programs
are invoked.
While it has a set of
.I builtin
functions which it performs directly,
most commands cause execution of programs that are, in fact,
external to the shell.
The shell is thus distinguished from the command interpreters of other
systems both by the fact that it is just a user program, and by the fact
that it is used almost exclusively as a mechanism for invoking other programs.
.PP
.I Commands
in the \s-2UNIX\s0 system consist of a list of strings or
.I words
interpreted as a
.I "command name"
followed by
.I arguments.
Thus the command
.DS
mail bill
.DE
consists of two words.
The first word
.I mail
names the command to be executed, in this case the
mail program which sends messages to other users.
The shell uses the name of the command in attempting to execute it for you.
It will look in a number of
.I directories
for a file with the name
.I mail
which is expected to contain the mail program.
.PP
The rest of the words of the command are given as
.I arguments
to the command itself when it is executed.
In this case we specified also the argument
.I bill
which is interpreted by the
.I mail
program to be the name of a user to whom mail is to be sent.
In normal terminal usage we might use the
.I mail
command as follows.
.DS
% mail bill
I have a question about the csh documentation.
My document seems to be missing page 5.
Does a page five exist?
	Bill
EOT
%
.DE
.PP
Here we typed a message to send to
.I bill
and ended this message with a ^D which sent an end-of-file to
the mail program.
(Here and throughout this document, the notation ``^\fIx\fR''
is to be read ``control-\fIx\fR'' and represents the striking of the \fIx\fR
key while the control key is held down.)
The mail program
then echoed the characters `EOT' and transmitted our message.
The characters `% ' were printed before and after the mail command 
by the shell to indicate that input was needed.
.PP
After typing the `% ' prompt the shell was reading command input from
our terminal.
We typed a complete command `mail bill'.
The shell then executed the
.I mail
program with argument
.I bill
and went dormant waiting for it to complete.
The mail program then read input from our terminal until we signalled
an end-of-file via typing a ^D after which the shell noticed
that mail had completed
and signaled us that it was ready to read from the terminal again by
printing another `% ' prompt.
.PP
This is the essential pattern of all interaction with \s-2UNIX\s0
through the shell.
A complete command is typed at the terminal, the shell executes
the command and when this execution completes, it prompts for a new command.
If you run the editor for an hour, the shell will patiently wait for
you to finish editing and obediently prompt you again whenever you finish
editing.
.PP
An example of a useful command you can execute now is the
.I tset
command, which sets the default
.I erase
and
.I kill
characters on your terminal \- the erase character erases the last
character you typed and the kill character erases the entire line you
have entered so far.
By default, the erase character is the delete key (equivalent to `^?')
and the kill character is `^U'.  Some people prefer to make the erase character
the backspace key (equivalent to `^H').
You can make this be true by typing
.DS
tset \-e
.DE
which tells the program
.I tset
to set the erase character to tset's default setting for this character
(a backspace).
.NH 2
Flag arguments
.PP
A useful notion in \s-2UNIX\s0 is that of a
.I flag
argument.
While many arguments to commands specify file names or user names,
some arguments rather specify an optional capability of the command
which you wish to invoke.
By convention, such arguments begin with the character `\-' (hyphen).
Thus the command
.DS
ls
.DE
will produce a list of the files in the current
.I "working directory" .
The option
.I \-s
is the size option, and
.DS
ls \-s
.DE
causes
.I ls
to also give, for each file the size of the file in blocks of 512
characters.
The manual section for each command in the \s-2UNIX\s0 reference manual
gives the available options for each command.
The
.I ls
command has a large number of useful and interesting options.
Most other commands have either no options or only one or two options.
It is hard to remember options of commands which are not used very
frequently, so most \s-2UNIX\s0 utilities perform only one or two functions
rather than having a large number of hard to remember options.
.NH 2
Output to files
.PP
Commands that normally read input or write output on the terminal 
can also be executed with this input and/or output done to
a file.
.PP
Thus suppose we wish to save the current date in a file called `now'.
The command
.DS
date
.DE
will print the current date on our terminal.
This is because our terminal is the default
.I "standard output"
for the date command and the date command prints the date on its
standard output.
The shell lets us
.I redirect
the
.I "standard output"
of a command through a
notation using the
.I metacharacter
`>' and the name of the file where output is to be placed.
Thus the command
.DS
date > now
.DE
runs the
.I date
command such that its standard output is
the file `now' rather than the terminal.
Thus this command places the current date and time into the file `now'.
It is important to know that the
.I date
command was unaware that its output was going to a file rather than
to the terminal.
The shell performed this
.I redirection
before the command began executing.
.PP
One other thing to note here is that the file `now'
need not have existed before the
.I date
command was executed; the shell would have created the file if it did
not exist.
And if the file did exist?