csh.1

来自「<B>Digital的Unix操作系统VAX 4.2源码</B>」· 1 代码 · 共 2,332 行 · 第 1/5 页

TERM into
.I term,
and
HOME into
.I home,
and copies these back into the environment whenever the normal
shell variables are reset.
The environment variable PATH is likewise handled.  It is not
necessary to worry about its setting other than in the file
.PN \&.cshrc
as inferior
.PN csh
processes will import the definition of
.I path
from the environment, and re-export it if you then change it.
.TP 15
.B argv
\c
Set to the arguments to the shell, it is from this variable that
positional parameters are substituted, that is `$1' is replaced by
`$argv[1]', and so forth.
.TP 15
.B cdpath
\c
Gives a list of alternate directories searched to find subdirectories
in
.I chdir
commands.
.TP 15
.B cwd
The full pathname of the current directory.
.TP 15
.B echo
\c
Set when the
.B \-x
command line option is given.
Causes each command and its arguments
to be echoed just before it is executed.
For non-built-in commands all expansions occur before echoing.
Built-in commands are echoed before command and file name substitution,
since these substitutions are then done selectively.
.TP 15
.B histchars
\c
Can be given a string value to change the characters used in history
substitution.  The first character of its value is used as the
history substitution character, replacing the default character !.
The second character of its value replaces the character ! in
quick substitutions.
.TP 15
.B history
\c
Can be given a numeric value to control the size of the history list.
Any command which has been referenced in this many events will not be
discarded.
Too large values of
.I history
may run the shell out of memory.
The last executed command is always saved on the history list.
.TP 15
.B home
\c
The home directory of the invoker, initialized from the environment.
The file name expansion of `\fB~\fR' refers to this variable.
.TP 15
.B ignoreeof
\c
If set the shell ignores
end-of-file from input devices which are terminals.
This prevents shells from accidentally being killed by control-D's.
.TP 15
.B mail
\c
The files where the shell checks for mail.
This is done after each command completion which will result in a prompt,
if a specified interval has elapsed.
The shell says `You have new mail.'
if the file exists with an access time not greater than its modify time.
.IP
If the first word of the value of
.I mail
is numeric it specifies a different mail checking interval, in seconds,
than the default, which is 10 minutes.
.IP
If multiple mail files are specified, then the shell says
`New mail in
.IR name '
when there is mail in the file
.I name.
.TP 15
.B noclobber
\c
As described in the section on
.I Input/output,
restrictions are placed on output redirection to insure that
files are not accidentally destroyed, and that `>>' redirections
refer to existing files.
.TP 15
.B noglob
\c
If set, file name expansion is inhibited.
This is most useful in shell scripts which are not dealing with file names,
or after a list of file names has been obtained and further expansions
are not desirable.
.TP 15
.B nonomatch
\c
If set, it is not an error for a file name expansion to not match any
existing files; rather the primitive pattern is returned.
It is still an error for the primitive pattern to be malformed, that is
`echo [' still gives an error.
.TP 15
.B notify
\c
If set, the shell notifies asynchronously of job completions.  The
default is to rather present job completions just before printing
a prompt.
.TP 15
.B path
\c
Each word of the path variable specifies a directory in which
commands are to be sought for execution.
A null word specifies the current directory.
If there is no
.I path
variable then only full path names will execute.
The usual search path is `.', `/bin' and `/usr/bin', but this
may vary from system to system.
For the super-user the default search path is `/etc', `/bin' and `/usr/bin'.
A shell which is given neither the
.B \-c
nor the
.B \-t
option will normally hash the contents of the directories in the
.I path
variable after reading
.PN \&.cshrc ,
and each time the
.I path
variable is reset.  If new commands are added to these directories
while the shell is active, it may be necessary to give the
.I rehash
or the commands may not be found.
.TP 15
.B prompt
\c
The string which is printed before each command is read from
an interactive terminal input.
If a `!' appears in the string it will be replaced by the current event number
unless a preceding `\e' is given.
Default is `% ', or `# ' for the super-user.
.TP 15
.B savehist
\c
is given a numeric value to control the number of entries of the
history list that are saved in ~/.history when the user logs out.
Any command which has been referenced in this many events will be saved.
During start up the shell sources ~/.history into the history list
enabling history to be saved across logins.
Too large values of
.I savehist
will slow down the shell during start up.
.TP 15
.B shell
\c
The file in which the shell resides.
This is used in forking shells to interpret files which have execute
bits set, but which are not executable by the system.
(See the description of
.I "Non-built-in Command Execution"
below.)
Initialized to the (system-dependent) home of the shell.
.TP 15
.B status
\c
The status returned by the last command.
If it terminated abnormally, then 0200 is added to the status.
Built-in commands which fail return exit status `1',
all other built-in commands set status `0'.
.TP 15
.B time
\c
Controls automatic timing of commands.
If set, then any command which takes more than this many cpu seconds
will cause a line giving user, system, and real times and a utilization
percentage which is the ratio of user plus system times to real time
to be printed when it terminates.
The 
.B time
command can be used to cause a command to be timed no matter how much 
CPU time it takes.  Thus
.EX
% time cp /etc/rc /usr/bill/rc
0.0u 0.1s 0:01 8% 2+1k 3+2io 1pf+0w
% time wc /etc/rc /usr/bill/rc
  52   178  1347 /etc/rc
  52   178  1347 /usr/bill/rc
  104  356  2694 total
0.1u 0.1s 0:00 13% 3+3k 5+3io 7pf+0w
%
.EE
The preceding example indicates that the 
.I cp 
command used a negligible amount of user time (u) and about 1/10th 
of a second system time (s); the elapsed time was 1 second (0:01), there was an average
memory usage of 2k bytes of program space and 1k bytes of data space over the cpu
time involved (2+1k); the program did three disk reads and two disk writes (3+2io),
and took one page fault and was not swapped (1pf+0w).  The word count command
.PN wc
on the other hand used 0.1 seconds of user time and 0.1 seconds of system time in
less than a second of elapsed time.  The percentage `13%' indicates that over the
period when it was active the command `wc' used an average of 13 percent of the
available CPU cycles of the machine.  
.TP 15
.B verbose
\c
Set by the
.B \-v
command line option, causes the words of each command to be printed
after history substitution.
.SH Non-built-in Command Execution
.NXR "csh command interpreter" "non-built-in commands"
When a command to be executed is found to not be a built-in command
the shell attempts to execute the command via
.MS execve 2 .
Each word in the variable
.I path
names a directory from which the shell will attempt to execute the command.
If it is given neither a
.B \-c
nor a
.B \-t
option, the shell will hash the names in these directories into an internal
table so that it will only try an
.I exec
in a directory if there is a possibility that the command resides there.
This greatly speeds command location when a large number of directories
are present in the search path.
If this mechanism has been turned off (via
.IR unhash ),
or if the shell was given a
.B \-c
or
.B \-t
argument, and in any case for each directory component of
.I path
which does not begin with a `/',
the shell concatenates with the given command name to form a path name
of a file which it then attempts to execute.
.PP
Parenthesized commands are always executed in a subshell.
Thus `(cd ; pwd) ; pwd' prints the
.I home
directory; leaving you where you were (printing this after the home directory),
while `cd ; pwd' leaves you in the
.I home
directory.
Parenthesized commands are most often used to prevent
.I chdir
from affecting the current shell.
.PP
If the file has execute permissions but is not an
executable binary to the system, then it is assumed to be a
file containing shell commands and a new shell is spawned to read it.
.PP
If there is an
.I alias
for
.I shell
then the words of the alias will be prepended to the argument list to form
the shell command.
The first word of the
.I alias
should be the full path name of the shell
(for example, `$shell').
Note that this is a special, late occurring, case of
.I alias
substitution,
and only allows words to be prepended to the argument list without modification.
.SH Argument List Processing
.NXR "csh command interpreter" "argument list processing"
If argument 0 to the shell is `\-' then this
is a login shell.
The flag arguments are interpreted as follows:
.TP 5
.B  \-c
\c
The first argument word is taken to be a command string.
All remaining argument words are placed in
.I argv.
.TP 5
.B  \-e
\c
The shell exits if any invoked command terminates abnormally
or yields a non-zero exit status.
.TP 5
.B  \-f
\c
The shell will start faster, because it will neither search for nor
execute commands from the file
`\&.cshrc' in the invokers home directory.
.TP 5
.B  \-i
\c
The shell is interactive and prompts for its top-level input,
even if stdin appears not to be a terminal.
Shells are interactive without this option if their inputs
and outputs are terminals.
.TP 5
.B  \-n
\c
Commands are parsed, but not executed.
This aids in syntactic checking of shell scripts.
.TP 5
.B  \-s
\c
Command input is taken from the standard input.
.TP 5
.B  \-t
\c
A single line of input is read and executed.
A `\e' may be used to escape the new line at the end of this
line and continue onto another line.
.TP 5
.B  \-v
\c
Causes the
.I verbose
variable to be set, with the effect
that command input is echoed after history substitution.
.TP 5
.B  \-x
\c
Causes the 
.I echo
variable to be set, so that commands are echoed immediately before execution.
.TP 5
.B  \-V
\c
Causes the
.I verbose
variable to be set even before `\&.cshrc' is executed.
.TP 5
.B  \-X
Causes the echo variable to be set before `\&.cshrc' is
executed.
.PP
After processing of flag arguments if arguments remain but none of the
.B \-c,
.B \-i,
.B \-s,
or
.B \-t
options was given the first argument is taken as the name of a file of
commands to be executed.
The shell opens this file, and saves its name for possible resubstitution
by `$0'.
Since many systems use either the standard version 6 or version 7 shells
whose shell scripts are not compatible with this shell, the shell will
execute such a `standard' shell if the first character of a script
is not a `#', that is if the script does not start with a comment.
Remaining arguments initialize the variable
.I argv.
.SH Signal Handling
.NXR "csh command interpreter" "signal handling"
The shell normally ignores
.I quit
signals.
Jobs running detached (either by `&' or the \fIbg\fR or \fB%... &\fR
commands) are immune to signals generated from the keyboard, including
hangups.
Other signals have the values which the shell inherited from its parent.
The shells handling of interrupts and terminate signals
in shell scripts can be controlled by
.I onintr.
Login shells catch the
.I terminate
signal; otherwise this signal is passed on to children from the state in the
shell's parent.
In no case are interrupts allowed when a login shell is reading the file
`\&.logout'.
.SH Command And Filename Recognition
The
.PN csh
command recognizes and completes user name aliases, commands (including
built-in
.PN csh
commands), and filenames.  To use this feature, do the following:
.TP 3
1.
Type enough characters at the prompt to make your input to
the system unique.
.TP
2. 
Press the ESC key.
.PP
If your input is unique, the Shell completes the input line.  If the
input is not unique, the terminal signals you with a beep.  If you
receive a beep, type CTRL/D for a list of options.  You can then
type the additional characters that will make your text unique.
After you have provided more input, press the ESC key again.
.SH Command Line Editing
The
.PN csh
command allows you to visually edit command lines using either a
.PN vi
or
.PN emacs
environment.  The
.PN vi
interface is modal and supports a subset of 
.PN vi
commands.  The
.PN emacs 
interface is modeless and supports a subset of
.PN emacs
commands.  See the Editing Interface section for a 
list of the available 
.PN vi
and 
.PN emacs
commands.
.PP
To set the editing environment, define the Shell environment
variable CSHEDIT as 
.PN vi
or 
.PN emacs .
If the environment variable CSHEDIT is not defined, the
.PN csh 
command searches for your EDITOR environment variable.  When your EDITOR
environment variable is set to 
.PN vi ,
.PN ex ,
.PN edit ,
or 
.PN ed ,
the 
.PN csh
command defaults to the 
.PN vi
command interface.  If your EDITOR environment is not set to any of
the previously mentioned editors, the default is the
.PN emacs
command interface.  Note that if neither the CSHEDIT or EDITOR
environment variables are defined, the 
.PN csh
command defaults to the 
.PN vi
command interface.
.PP
The new history modifier (:v) allows you to pull commands from the
history list to make them available for editing 
in visual edit mode.  The symbol :v tells the Shell that
you want to enter visual edit mode.  For example, the following 
command line invokes edit mode for the previously typed 
.PN cp
command line:
.EX
!cp:v
.EE
When you press the ESC key as the first character on a command line,
it is equivalent to typing t