csh.g

早期freebsd实现

variable is
.DS
path	(. /usr/ucb /bin /usr/bin)
.DE
the shell normally looks in the current directory, and then in
the standard system directories `/usr/ucb', `/bin' and `/usr/bin' for the named
command (2.2).
If the command cannot be found the shell will print an error diagnostic.
Scripts of shell commands will be executed using another shell to interpret
them if they have `execute' permission set.
This is normally true because a command of the form
.DS
chmod 755 script
.DE
was executed to turn this execute permission on (3.3).
If you add new commands to a directory in the 
.I path , 
you should issue
the command 
.I rehash 
(2.2).
.IP pathname
A list of names, separated by `/' characters, forms a
.I pathname.
Each
.I component,
between successive `/' characters, names a directory
in which the next 
.I component 
file resides.
.I Pathnames 
which begin with the character `/' are interpreted relative
to the
.I root
directory in the filesystem.
Other 
.I pathnames 
are interpreted relative to the current directory
as reported by
.I pwd.
The last component of a 
.I pathname 
may name a directory, but
usually names a file.
.IP pipeline
A group of commands which are connected together, the 
.I "standard output"
of each connected to the 
.I "standard input" 
of the next,
is called a
.I pipeline.
The
.I pipe
mechanism used to connect these commands is indicated by
the shell metacharacter `|' (1.5, 2.3).
.IP popd
The
.I popd
command changes the shell's
.I "working directory"
to the directory you most recently left using the
.I pushd
command.  It returns to the directory without having to type its name,
forgetting the name of the current
.I "working directory"
before doing so (2.7).
.IP port
The part of a computer system to which each terminal is
connected is called a
.I port .
Usually the system has a fixed number of
.I ports ,
some of which are connected to telephone lines
for dial-up access, and some of which are permanently
wired directly to specific terminals.
.IP pr
The
.I pr
command is used to prepare listings of the contents of files
with headers giving the name of the file and the date and
time at which the file was last modified (2.3).
.IP printenv
The
.I printenv
command is used
to print the current setting of variables in the environment
(2.8).
.IP process
An instance of a running program is called a 
.I process 
(2.6).
\s-2UNIX\s0 assigns each 
.I process 
a unique number when it is 
started \- called the
.I "process number" .
.I "Process numbers" 
can be used to stop individual 
.I processes
using the 
.I kill
or
.I stop
commands when the
.I processes
are part of a detached
.I background
job.
.IP program
Usually synonymous with
.I command ;
a binary file or shell command script
which performs a useful function is often
called a 
.I program .
.IP prompt
Many programs will print a 
.I prompt 
on the terminal when they expect input.
Thus the editor
`ex (1)' will print a `:' when it expects input.
The shell 
.I prompts
for input with `% ' and occasionally with `? ' when
reading commands from the terminal (1.1).
The shell has a variable
.I prompt
which may be set to a different value to change the shell's main 
.I prompt .
This is mostly used when debugging the shell (2.8).
.IP pushd
The
.I pushd
command, which means `push directory', changes the shell's
.I "working directory"
and also remembers the current
.I "working directory"
before the change is made, allowing you to return to the same
directory via the
.I popd
command later without retyping its name (2.7).
.IP ps
The
.I ps
command is used to show the processes you are currently running.
Each process is shown with its unique process number,
an indication of the terminal name it is attached to,
an indication of the state of the process (whether it is running,
stopped, awaiting some event (sleeping), and whether it is swapped out),
and the amount of \s-2CPU\s0 time it has used so far.
The command is identified by printing some of the words used
when it was invoked (2.6).
Shells, such as the
.I csh
you use to run the 
.I ps 
command, are not normally shown in the output.
.IP pwd
The
.I pwd
command prints the full 
.I pathname 
of the current
.I "working directory" \&.
The
.I dirs
builtin command is usually a better and faster choice.
.IP quit
The
.I quit
signal, generated by a control-\e,
is used to terminate programs which are behaving unreasonably.
It normally produces a core image file (1.8).
.IP quotation
The process by which metacharacters are prevented their special
meaning, usually by using the character `\' in pairs, or by
using the character `\e', is referred to as
.I quotation
(1.7).
.IP redirection
The routing of input or output from or to a file is known
as
.I redirection
of input or output (1.3).
.IP rehash
The
.I rehash
command tells the shell to rebuild its internal table of which commands
are found in which directories in your
.I path .
This is necessary when a new program is installed in one of these
directories (2.8).
.IP "relative pathname"
.br
A
.I pathname
which does not begin with a `/' is called a
.I "relative pathname"
since it is interpreted
.I relative
to the current 
.I "working directory" .
The first
.I component
of such a
.I pathname
refers to some file or directory in the
.I "working directory" ,
and subsequent
.I components
between `/' characters refer to directories below the
.I "working directory" .
.I Pathnames
that are not
.I relative
are called
.I "absolute pathnames"
(1.6).
.IP repeat
The
.I repeat
command iterates another command a specified number of times.
.IP root
The directory
that is at the top of the entire directory structure is called the
.I root
directory since it is the `root' of the entire tree structure of
directories.  The name used in
.I pathnames
to indicate the
.I root
is `/'.  
.I Pathnames 
starting with `/' are said to be
.I absolute
since they start at the
.I root
directory.
.I Root
is also used as the part of a 
.I pathname 
that is left after removing
the 
.I extension .
See
.I filename
for a further explanation (1.6).
.IP \s-2RUBOUT\s0
The \s-2RUBOUT\s0 or \s-2DELETE\s0
key is often used to erase the previously typed character; some users
prefer the \s-2BACKSPACE\s0 for this purpose.  On older versions of \s-2UNIX\s0
this key served as the \s-2INTR\s0 character.
.IP "scratch file"
Files whose names begin with a `#' are referred to as 
.I "scratch files" ,
since they are automatically removed by the system after a couple of
days of non-use, or more frequently if disk space becomes tight (1.3).
.IP script
Sequences of shell commands placed in a file are called shell command 
.I scripts .
It is often possible to perform simple tasks using these 
.I scripts 
without writing a program in a language such as C, by
using the shell to selectively run other programs (3.3, 3.10).
.IP set
The builtin
.I set
command is used to assign new values to shell variables
and to show the values of the current variables.
Many shell variables have special meaning to the shell itself.
Thus by using the 
.I set 
command the behavior of the shell can be affected (2.1).
.IP setenv
Variables in the environment `environ (5)'
can be changed by using the
.I setenv
builtin command (2.8).
The
.I printenv
command can be used to print the value of the variables in the environment.
.IP shell
A 
.I shell 
is a command language interpreter.
It is possible to write and run your own 
.I shell ,
as 
.I shells 
are no different than any other programs as far as the
system is concerned.
This manual deals with the details of one particular 
.I shell ,
called
.I csh.
.IP "shell script"
See
.I script
(3.3, 3.10).
.IP signal
A
.I signal
in \s-2UNIX\s0 is a short message that is sent to a running program
which causes something to happen to that process.
.I Signals
are sent either by typing special
.I control
characters on the keyboard or by using the
.I kill
or
.I stop
commands (1.8, 2.6).
.IP sort
The
.I sort
program sorts a sequence of lines in ways that can be controlled
by argument 
.I flags 
(1.5).
.IP source
The
.I source
command causes the shell to read commands from a specified file.
It is most useful for reading files such as
.I \&.cshrc
after changing them (2.8).
.IP "special character"
.br
See
.I metacharacters
and the
appendix to this manual.
.IP standard
We refer often to the
.I "standard input"
and
.I "standard output"
of commands.
See
.I input
and
.I output
(1.3, 3.8).
.IP status
A command normally returns a
.I status
when it finishes.
By convention a
.I status
of zero indicates that the command succeeded.
Commands may return non-zero 
.I status 
to indicate that some abnormal event has occurred.
The shell variable
.I status
is set to the 
.I status 
returned by the last command.
It is most useful in shell commmand scripts (3.6).
.IP stop
The
.I stop
command causes a
.I background 
job to become 
.I suspended 
(2.6).
.IP string
A sequential group of characters taken together is called a
.I string \&.
.I Strings
can contain any printable characters (2.2).
.IP stty
The
.I stty
program changes certain parameters inside \s-2UNIX\s0 which determine
how your terminal is handled.  See `stty (1)' for a complete description (2.6).
.IP substitution
The shell implements a number of
.I substitutions
where sequences indicated by metacharacters are replaced by other sequences.
Notable examples of this are history 
.I substitution 
keyed by the
metacharacter `!' and variable 
.I substitution 
indicated by `$'.
We also refer to 
.I substitutions 
as
.I expansions
(3.4).
.IP suspended
A job becomes
.I suspended
after a \s-2STOP\s0 signal is sent to it, either by typing a
.I control -z
at the terminal (for
.I foreground
jobs) or by using the
.I stop
command (for
.I background
jobs).  When
.I suspended ,
a job temporarily stops running until it is restarted by either the
.I fg
or
.I bg
command (2.6).
.IP switch
The
.I switch
command of the shell allows the shell
to select one of a number of sequences of commands based on an
argument string.
It is similar to the
.I switch
statement in the language C (3.7).
.IP termination
When a command which is being executed finishes we say it undergoes
.I termination
or
.I terminates.
Commands normally terminate when they read an 
.I end\f1-\fPof\f1-\fPfile
from their 
.I "standard input" .
It is also possible to terminate commands by sending them
an
.I interrupt
or
.I quit
signal (1.8).
The
.I kill
program terminates specified jobs (2.6).
.IP then
The
.I then
command is part of the shell's
`if-then-else-endif' control construct used in command scripts (3.6).
.IP time
The
.I time
command can be used to measure the amount of \s-2CPU\s0
and real time consumed by a specified command as well
as the amount of disk i/o, memory utilized, and number
of page faults and swaps taken by the command (2.1, 2.8).
.IP tset
The
.I tset
program is used to set standard erase and kill characters
and to tell the system what kind of terminal you are using.
It is often invoked in a
.I \&.login
file (2.1).
.IP tty
The word
.I tty
is a historical abbreviation for `teletype' which is frequently used
in \s-2UNIX\s0 to indicate the
.I port
to which a given terminal is connected.  The
.I tty
command will print the name of the
.I tty
or
.I port
to which your terminal is presently connected.
.IP unalias
The
.I unalias
command removes aliases (2.8).
.IP \s-2UNIX\s0
\s-2UNIX\s0 is an operating system on which
.I csh
runs.
\s-2UNIX\s0 provides facilities which allow
.I csh
to invoke other programs such as editors and text formatters which
you may wish to use.
.IP unset
The
.I unset
command removes the definitions of shell variables (2.2, 2.8).
.IP "variable expansion"
.br
See
.I variables
and
.I expansion
(2.2, 3.4).
.IP variables
.I Variables 
in
.I csh
hold one or more strings as value.
The most common use of 
.I variables 
is in controlling the behavior
of the shell.
See
.I path ,
.I noclobber ,
and
.I ignoreeof
for examples.
.I Variables 
such as
.I argv
are also used in writing shell programs (shell command scripts)
(2.2).
.IP verbose
The
.I verbose
shell variable can be set to cause commands to be echoed
after they are history expanded.
This is often useful in debugging shell scripts.
The
.I verbose
variable is set by the shell's
.I \-v
command line option (3.10).
.IP wc
The
.I wc
program calculates the number of characters, words, and lines in the
files whose names are given as arguments (2.6).
.IP while
The
.I while
builtin control construct is used in shell command scripts (3.7).
.IP word
A sequence of characters which forms an argument to a command is called
a
.I word .
Many characters which are neither letters, digits, `\-', `.' nor `/'
form 
.I words 
all by themselves even if they are not surrounded
by blanks.
Any sequence of characters may be made into a 
.I word 
by surrounding it
with `\'' characters
except for the characters `\'' and `!' which require special treatment
(1.1).
This process of placing special characters in 
.I words 
without their special meaning is called
.I quoting .
.IP "working directory"
.br
At any given time you are in one particular directory, called
your 
.I "working directory" .
This directory's name is printed by the
.I pwd
command and the files listed by
.I ls
are the ones in this directory.
You can change 
.I "working directories" 
using
.I chdir .
.IP write
The
.I write
command is an obsolete way of communicating with other users who are logged in to
\s-2UNIX\s0 (you have to take turns typing).  If you are both using display 
terminals, use \fItalk\fP(1), which is much more pleasant.