csh.1

早期freebsd实现

.It Ic unhash
Use of the internal hash table to speed location of executed programs
is disabled.
.Pp
.It Ic unlimit
.It Ic unlimit Ar  resource
.It Ic unlimit Fl h
.It Ic unlimit Fl h Ar resource
Removes the limitation on
.Ar resource  .
If no
.Ar resource
is specified, then all
.Ar resource
limitations are removed.  If
.Fl h
is given, the corresponding hard limits are removed.  Only the
super-user may do this.
.Pp
.It Ic unset Ar pattern
All variables whose names match the specified pattern are removed.
Thus all variables are removed by `unset *'; this has noticeably
distasteful side-effects.
It is not an error for nothing to be
.Ic unset .
.Pp
.It Ic unsetenv Ar pattern
Removes all variables whose name match the specified pattern from the
environment.  See also the
.Ic setenv
command above and
.Xr printenv  1  .
.Pp
.It Ic wait
Wait for all background jobs.
If the shell is interactive, then an interrupt can disrupt the wait.
After the interrupt, the shell prints names and job numbers of all jobs
known to be outstanding.
.It Ic which Ar command
Displays the resolved command that will be executed by the shell.
.Pp
.It Ic while Ar (expr)
.It \&...
.It Ic end
While the specified expression evaluates non-zero, the commands between
the
.Ic while
and the matching
.Ic end
are evaluated.
.Ic Break
and
.Ic continue
may be used to terminate or continue the loop prematurely.
(The
.Ic while
and
.Ic end
must appear alone on their input lines.)
Prompting occurs here the first time through the loop as for the
.Ic foreach
statement if the input is a terminal.
.Pp
.It Ic % Ns Ar job
Brings the specified job into the foreground.
.Pp
.It Ic % Ns Ar job Ic &
Continues the specified job in the background.
.Pp
.It Ic @
.It Ic @ Ns Ar name Ns = expr
.It Ic @ Ns Ar name[index] Ns = expr
The first form prints the values of all the shell variables.
The second form sets the specified
.Ar name
to the value of
.Ar expr .
If the expression contains `<', `>', `&' or `|' then at least
this part of the expression must be placed within `(' `)'.
The third form assigns the value of
.Ar expr
to the
.Ar index Ns 'th
argument of
.Ar name .
Both
.Ar name
and its
.Ar index Ns 'th
component must already exist.
.El
.Pp
The operators `*=', `+=', etc are available as in C.
The space separating the name from the assignment operator is optional.
Spaces are, however, mandatory in separating components of
.Ar expr
which would otherwise be single words.
.Pp
Special postfix `+\|+' and `\-\|\-' operators increment and decrement
.Ar name
respectively, i.e., `@  i++'.
.Ss Pre-defined and environment variables
The following variables have special meaning to the shell.
Of these,
.Ar argv ,
.Ar cwd,
.Ar home ,
.Ar path,
.Ar prompt ,
.Ar shell
and
.Ar status
are always set by the shell.
Except for
.Ar cwd
and
.Ar status ,
this setting occurs only at initialization;
these variables will not then be modified unless done
explicitly by the user.
.Pp
The shell copies the environment variable
.Ev USER
into the variable
.Ar user ,
.Ev TERM
into
.Ar term ,
and
.Ev HOME
into
.Ar home ,
and copies these back into the environment whenever the normal
shell variables are reset.
The environment variable
.Ev PATH
is likewise handled; it is not
necessary to worry about its setting other than in the file
.Ar \&.cshrc
as inferior
.Nm csh
processes will import the definition of
.Ar path
from the environment, and re-export it if you then change it.
.Bl -tag -width histchars
.It Ic argv
Set to the arguments to the shell, it is from this variable that
positional parameters are substituted, i.e., `$1' is replaced by
`$argv[1]',
etc.
.It Ic cdpath
Gives a list of alternate directories searched to find subdirectories
in
.Ar chdir
commands.
.It Ic cwd
The full pathname of the current directory.
.It Ic echo
Set when the
.Fl x
command line option is given.
Causes each command and its arguments
to be echoed just before it is executed.
For non-builtin commands all expansions occur before echoing.
Builtin commands are echoed before command and filename substitution,
since these substitutions are then done selectively.
.It Ic filec
Enable file name completion.
.It Ic histchars
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 `\(ua' in
quick substitutions.
.It Ic histfile
Can be set to the pathname where history is going to be saved/restored.
.It Ic history
Can be given a numeric value to control the size of the history list.
Any command that has been referenced in this many events will not be
discarded.
Too large values of
.Ar history
may run the shell out of memory.
The last executed command is always saved on the history list.
.It Ic home
The home directory of the invoker, initialized from the environment.
The filename expansion of
.Sq Pa ~
refers to this variable.
.It Ic ignoreeof
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.
.It Ic mail
The files where the shell checks for mail.
This checking is done after each command completion that 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.
.Pp
If the first word of the value of
.Ar mail
is numeric it specifies a different mail checking interval, in seconds,
than the default, which is 10 minutes.
.Pp
If multiple mail files are specified, then the shell says
`New mail in
.Ar name Ns '
when there is mail in the file
.Ar name .
.It Ic noclobber
As described in the section on
.Sx input/output ,
restrictions are placed on output redirection to insure that
files are not accidentally destroyed, and that `>>' redirections
refer to existing files.
.It Ic noglob
If set, filename expansion is inhibited.
This inhibition is most useful in shell scripts that
 are not dealing with filenames,
or after a list of filenames has been obtained and further expansions
are not desirable.
.It Ic nonomatch
If set, it is not an error for a filename expansion to not match any
existing files; instead the primitive pattern is returned.
It is still an error for the primitive pattern to be malformed, i.e.,
`echo ['
still gives an error.
.It Ic notify
If set, the shell notifies asynchronously of job completions;
the default is to present job completions just before printing
a prompt.
.It Ic path
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
.Ar 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 that is given neither the
.Fl c
nor the
.Fl t
option will normally hash the contents of the directories in the
.Ar path
variable after reading
.Ar \&.cshrc ,
and each time the
.Ar path
variable is reset.  If new commands are added to these directories
while the shell is active, it may be necessary to do a
.Ic rehash
or the commands may not be found.
.It Ic prompt
The string that 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.
.It Ic savehist
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 that 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
.Ar savehist
will slow down the shell during start up.
If
.Ar savehist
is just set, the shell will use the value of
.Ar history.
.It Ic shell
The file in which the shell resides.
This variable is used in forking shells to interpret files that have execute
bits set, but which are not executable by the system.
(See the description of
.Sx Non-builtin Command Execution
below.)
Initialized to the (system-dependent) home of the shell.
.It Ic status
The status returned by the last command.
If it terminated abnormally, then 0200 is added to the status.
Builtin commands that fail return exit status `1',
all other builtin commands set status to `0'.
.It Ic time
Controls automatic timing of commands.
If set, then any command that 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.
.It Ic verbose
Set by the
.Fl v
command line option, causes the words of each command to be printed
after history substitution.
.El
.Ss Non-builtin command execution
When a command to be executed is found to not be a builtin command
the shell attempts to execute the command via
.Xr execve  2  .
Each word in the variable
.Ar path
names a directory from which the shell will attempt to execute the command.
If it is given neither a
.Fl c
nor a
.Fl t
option, the shell will hash the names in these directories into an internal
table so that it will only try an
.Ic exec
in a directory if there is a possibility that the command resides there.
This shortcut greatly speeds command location when many directories
are present in the search path.
If this mechanism has been turned off (via
.Ic unhash ) ,
or if the shell was given a
.Fl c
or
.Fl t
argument, and in any case for each directory component of
.Ar path
that 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
.Pp
.Dl (cd ; pwd) ; pwd
.Pp
prints the
.Ar home
directory; leaving you where you were (printing this after the home directory),
while
.Pp
.Dl cd ; pwd
.Pp
leaves you in the
.Ar home
directory.
Parenthesized commands are most often used to prevent
.Ic 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
.Ic alias
for
.Ic shell
then the words of the alias will be prepended to the argument list to form
the shell command.
The first word of the
.Ic alias
should be the full path name of the shell
(e.g., `$shell').
Note that this is a special, late occurring, case of
.Ic alias
substitution,
and only allows words to be prepended to the argument list without change.
.Ss Signal handling
The shell normally ignores
.Ar quit
signals.
Jobs running detached (either by
.Ic \&&
or the
.Ic bg
or
.Ic %... &
commands) are immune to signals generated from the keyboard, including
hangups.
Other signals have the values which the shell inherited from its parent.
The shell's handling of interrupts and terminate signals
in shell scripts can be controlled by
.Ic onintr .
Login shells catch the
.Ar terminate
signal; otherwise this signal is passed on to children from the state in the
shell's parent.
Interrupts are not allowed when a login shell is reading the file
.Pa \&.logout .
.Sh AUTHOR
William Joy.
Job control and directory stack features first implemented by J.E. Kulp of
IIASA, Laxenburg, Austria,
with different syntax than that used now.
File name completion code written by Ken Greer, HP Labs.
Eight-bit implementation Christos S. Zoulas, Cornell University.
.Sh FILES
.Bl -tag -width /etc/passwd -compact
.It Pa ~/.cshrc
Read at beginning of execution by each shell.
.It Pa ~/.login
Read by login shell, after `.cshrc' at login.
.It Pa ~/.logout
Read by login shell, at logout.
.It Pa /bin/sh
Standard shell, for shell scripts not starting with a `#'.
.It Pa /tmp/sh*
Temporary file for `<<'.
.It Pa /etc/passwd
Source of home directories for `~name'.
.El
.Sh LIMITATIONS
Word lengths \-
Words can be no longer than 1024 characters.
The system limits argument lists to 10240 characters.
The number of arguments to a command that involves filename expansion
is limited to 1/6'th the number of character