csh.g

早期freebsd实现

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.\"	@(#)csh.g	8.1 (Berkeley) 6/8/93
.\"
.SH
Glossary
.PP
This glossary lists the most important terms introduced in the
introduction to the
shell and gives references to sections of the shell
document for further information about them.
References of the form
`pr (1)'
indicate that the command
.I pr
is in the \s-2UNIX\s0 User Reference manual in section 1.
You can look at an online copy of its manual page by doing
.DS
man 1 pr
.DE
References of the form (2.5)
indicate that more information can be found in section 2.5 of this
manual.
.IP \&\fB.\fR 15n
Your current directory has the name `.' as well as the name printed
by the command
.I pwd;
see also
.I dirs.
The current directory `.' is usually the first 
.I component 
of the search path contained in the variable
.I path ,
thus commands which are in `.' are found first (2.2).
The character `.' is also used in separating 
.I components 
of filenames
(1.6).
The character `.' at the beginning of a 
.I component 
of a 
.I pathname 
is treated specially and not matched by the 
.I "filename expansion"
metacharacters `?', `*', and `[' `]' pairs (1.6).
.IP \&\fB..\fR
Each directory has a file `..' in it which is a reference to its
parent directory.
After changing into the directory with
.I chdir ,
i.e.
.DS
chdir paper
.DE
you can return to the parent directory by doing
.DS
chdir ..
.DE
The current directory is printed by
.I pwd
(2.7).
.IP a.out
Compilers which create executable images create them, by default, in the
file 
.I a.out.
for historical reasons (2.3).
.IP "absolute pathname"
.br
A 
.I pathname 
which begins with a `/' is
.I absolute
since it specifies the 
.I path 
of directories from the beginning
of the entire directory system \- called the
.I root
directory.  
.I Pathname s 
which are not
.I absolute
are called
.I relative
(see definition of
.I "relative pathname" )
(1.6).
.IP alias
An
.I alias
specifies a shorter or different name for a \s-2UNIX\s0
command, or a transformation on a command to be performed in
the shell.
The shell has a command
.I alias
which establishes 
.I aliases 
and can print their current values.
The command
.I unalias
is used to remove 
.I aliases 
(2.4).
.IP argument
Commands in \s-2UNIX\s0 receive a list of 
.I argument 
words.
Thus the command
.DS
echo a b c
.DE
consists of the
.I "command name"
`echo' and three 
.I argument 
words `a', `b' and `c'.
The set of 
.I arguments 
after the
.I "command name"
is said to be the
.I "argument list"
of the command (1.1).
.IP argv
The list of arguments to a command written in the shell language
(a shell script or shell procedure) is stored in a variable called
.I argv
within the shell.
This name is taken from the conventional name in the
C programming language (3.4).
.IP background
Commands started without waiting for them to complete are called
.I background
commands (2.6).
.IP base
A filename is sometimes thought of as consisting of a
.I base
part, before any `.' character, and an 
.I extension 
\- the part after
the `.'.  See
.I filename
and
.I extension
(1.6) and basename (1).
.IP bg
The
.I bg
command causes a
.I suspended 
job to continue execution in the
.I background
(2.6).
.IP bin
A directory containing binaries of programs and shell scripts to be
executed is typically called a 
.I bin 
directory.
The standard system 
.I bin 
directories are `/bin' containing the most
heavily used commands and `/usr/bin' which contains most other user
programs.
Programs developed at UC Berkeley live in `/usr/ucb', while locally
written programs live in `/usr/local'.  Games are kept in the directory
`/usr/games'.
You can place binaries in any directory.
If you wish to execute them often, the name of the directories
should be a 
.I component 
of the variable
.I path .
.IP break
.I Break
is a builtin command used to exit from loops within the control
structure of the shell (3.7).
.IP breaksw
The
.I breaksw
builtin command is used to exit from a
.I switch
control structure, like a
.I break
exits from loops (3.7).
.IP builtin
A command executed directly by the shell is called a
.I builtin
command.
Most commands in \s-2UNIX\s0 are not built into the shell,
but rather exist as files in 
.I bin 
directories.
These commands are accessible because the directories in which
they reside are named in the
.I path
variable.
.IP case
A
.I case
command is used as a label in a
.I switch
statement in the shell's control structure, similar to that of the
language C.
Details are given in the shell documentation `csh (1)' (3.7).
.IP cat
The
.I cat
program catenates a list of specified files on the 
.I "standard output" .
It is usually used to look at the contents of a single file on the terminal,
to `cat a file' (1.8, 2.3).
.IP cd
The
.I cd
command is used to change the 
.I "working directory" .
With no arguments,
.I cd
changes your 
.I "working directory" 
to be your
.I home
directory (2.4, 2.7).
.IP chdir
The
.I chdir
command is a synonym for
.I cd .
.I Cd
is usually used because it is easier to type.
.IP chsh
The
.I chsh
command is used to change the shell which you use on \s-2UNIX\s0.
By default, you use an different version of the shell
which resides in `/bin/sh'.
You can change your shell to `/bin/csh' by doing
.DS
chsh your-login-name /bin/csh
.DE
Thus I would do
.DS
chsh bill /bin/csh
.DE
It is only necessary to do this once.
The next time you log in to \s-2UNIX\s0 after doing this command,
you will be using
.I csh
rather than the shell in `/bin/sh' (1.9).
.IP cmp
.I Cmp
is a program which compares files.
It is usually used on binary files, or to see if two files are identical (3.6).
For comparing text files the program
.I diff ,
described in `diff (1)' is used.
.IP command
A function performed by the system, either by the shell
(a builtin 
.I command )
or by a program residing in a file in
a directory within the \s-2UNIX\s0 system, is called a
.I command
(1.1).
.IP "command name"
.br
When a command is issued, it consists of a
.I "command name" ,
which is the first word of the command,
followed by arguments.
The convention on \s-2UNIX\s0 is that the first word of a
command names the function to be performed (1.1).
.IP "command substitution"
.br
The replacement of a command enclosed in `\`' characters
by the text output by that command 
is called
.I "command substitution"
(4.3).
.IP component
A part of a
.I pathname
between `/' characters is called a
.I component
of that 
.I pathname .
A variable
which has multiple strings as value is said to have
several
.I component s;
each string is a
.I component
of the variable.
.IP continue
A builtin command which causes execution of the enclosing
.I foreach
or
.I while
loop to cycle prematurely.
Similar to the
.I continue
command in the programming language C (3.6).
.IP control-
Certain special characters, called
.I control
characters, are produced by holding down the \s-2CONTROL\s0 key
on your terminal and simultaneously pressing another character, much like
the \s-2SHIFT\s0 key is used to produce upper case characters. Thus
.I control- c
is produced by holding down the \s-2CONTROL\s0 key while pressing the
`c' key.  Usually \s-2UNIX\s0 prints an caret (^) followed by the
corresponding letter when you type a
.I control
character (e.g. `^C' for
.I control- c
(1.8).
.IP "core\ dump"
When a program terminates abnormally, the system places an image
of its current state in a file named `core'.
This 
.I "core dump"
can be examined with the system debugger `adb (1)'
or `sdb (1)' in order to determine what went wrong with the program (1.8).
If the shell produces a message of the form
.DS
Illegal instruction (core dumped)
.DE
(where `Illegal instruction' is only one of several possible
messages), you should report this to the author of the program
or a system administrator, 
saving the `core' file.
.IP cp
The
.I cp
(copy) program is used to copy the contents of one file into another
file.
It is one of the most commonly used \s-2UNIX\s0 commands (1.6).
.IP csh
The name of the shell
program that this document describes.
.IP \&.cshrc
The file
.I \&.cshrc
in your
.I home
directory is read by each shell as it begins execution.
It is usually used to change the setting of the variable
.I path
and to set
.I alias
parameters which are to take effect globally (2.1).
.IP cwd
The
.I cwd
variable in the shell holds the
.I "absolute pathname"
of the current
.I "working directory" \&.
It is changed by the shell whenever your current
.I "working directory"
changes and should not be changed otherwise (2.2).
.IP date
The
.I date
command prints the current date and time (1.3).
.IP debugging
.I Debugging
is the process of correcting mistakes in programs and shell scripts.
The shell has several options and variables which may be used
to aid in shell 
.I debugging 
(4.4).
.IP default:
The label
.I default:
is used within shell
.I switch
statements, as it is in the C language
to label the code to be executed if none of the
.I case
labels matches the value switched on (3.7).
.IP \s-2DELETE\s0
The
\s-2DELETE\s0
or
\s-2RUBOUT\s0
key on the terminal normally causes an interrupt to be sent to the current job.
Many users change the interrupt character to be ^C.
.IP detached
A command that continues running in the 
.I background 
after you logout is said to be 
.I detached .
.IP diagnostic
An error message produced by a program is often referred to as a
.I diagnostic .
Most error messages are not written to the 
.I "standard output" ,
since that is often directed away from the terminal (1.3, 1.5).
Error messsages are instead written to the
.I "diagnostic output"
which may be directed away from the terminal, but usually is not.
Thus 
.I diagnostics 
will usually appear on the terminal (2.5).
.IP directory
A structure which contains files.
At any time you are in one particular 
.I directory 
whose names can be printed by the command 
.I pwd .
The
.I chdir
command will change you to another 
.I directory , 
and make the files
in that 
.I directory 
visible. The 
.I directory 
in which you are when you first login is your
.I home
directory (1.1, 2.7).
.IP "directory\ stack"
The shell saves the names of previous
.I "working directories"
in the
.I "directory stack"
when you change your current
.I "working directory"
via the
.I pushd
command.  The
.I "directory stack"
can be printed by using the
.I dirs
command, which includes your current
.I "working directory"
as the first directory name on the left (2.7).
.IP dirs
The
.I dirs
command prints the shell's
.I "directory stack" 
(2.7).
.IP du
The
.I du
command is a program (described in `du (1)') which
prints the number of disk blocks is all directories below
and including your current
.I "working directory"
(2.6).
.IP echo
The
.I echo
command prints its arguments (1.6, 3.6).
.IP else
The
.I else
command is part of the `if-then-else-endif' control
command construct (3.6).
.IP endif
If an
.I if
statement is ended with the word
.I then ,
all lines following the
.I if
up to a line starting with the word
.I endif
or
.I else
are executed if the condition between parentheses after the
.I if
is true (3.6).
.IP \s-2EOF\s0
An
.I "end\f1-\fPof\f1-\fPfile"
is generated by the terminal by a control-d,
and whenever a command reads to the end of a file which
it has been given as input.
Commands receiving input from a
.I pipe
receive an 
.I "end\f1-\fPof\f1-\fPfile" 
when the command sending them input completes.
Most commands terminate when they receive an 
.I "end\f1-\fPof\f1-\fPfile" .
The shell has an option to ignore 
.I "end\f1-\fPof\f1-\fPfile" 
from a terminal
input which may help you keep from logging out accidentally
by typing too many control-d's (1.1, 1.8, 3.8).
.IP escape
A character `\e' used to prevent the special meaning of a metacharacter
is said to
.I escape
the character from its special meaning.
Thus
.DS
echo \e*
.DE
will echo the character `*' while just
.DS
echo *
.DE
will echo the names of the file in the current directory.
In this example, \e
.I escape s
`*' (1.7).
There is also a non-printing character called
.I escape , 
usually labelled
\s-2ESC\s0
or
\s-2ALTMODE\s0
on terminal keyboards.
Some older \s-2UNIX\s0 systems use this character to indicate that
output is to be 
.I suspended . 
Most systems use control-s to stop the output and control-q to start it.
.IP /etc/passwd
This file contains information about the accounts currently on the
system.
It consists of a line for each account with fields separated by
`:' characters (1.8).
You can look at this file by saying
.DS
cat /etc/passwd
.DE
The commands
.I finger
and
.I grep
are often used to search for information in this file.
See `finger (1)', `passwd(5)', and `grep (1)' for more details.
.IP exit
The
.I exit
command is used to force termination of a shell script,
and is built into the shell (3.9).
.IP "exit\ status"
A command which discovers a problem may reflect this back to the command
(such as a shell) which invoked (executed) it.
It does this by returning a non-zero number as its