csh.1

早期freebsd实现

Standing alone, i.e., `~' it expands to the invokers home directory as reflected
in the value of the variable
.Ar home .
When followed by a name consisting of letters, digits and `\-' characters,
the shell searches for a user with that name and substitutes their
home directory;  thus `~ken' might expand to `/usr/ken' and `~ken/chmach'
to `/usr/ken/chmach'.
If the character `~' is followed by a character other than a letter or `/'
or does not appear at the beginning of a word,
it is left undisturbed.
.Pp
The metanotation `a{b,c,d}e' is a shorthand for `abe ace ade'.
Left to right order is preserved, with results of matches being sorted
separately at a low level to preserve this order.
This construct may be nested.
Thus, `~source/s1/{oldls,ls}.c' expands to
`/usr/source/s1/oldls.c /usr/source/s1/ls.c'
without chance of error
if the home directory for `source' is `/usr/source'.
Similarly `../{memo,*box}' might expand to `../memo ../box ../mbox'.
(Note that `memo' was not sorted with the results of the match to `*box'.)
As a special case `{', `}' and `{}' are passed undisturbed.
.Ss Input/output
The standard input and the standard output of a command may be redirected
with the following syntax:
.Pp
.Bl -tag -width Ds -compact -offset indent
.It < name
Open file
.Ar name
(which is first variable, command and filename expanded) as the standard
input.
.It << word
Read the shell input up to a line that is identical to
.Ar word .
.Ar Word
is not subjected to variable, filename or command substitution,
and each input line is compared to
.Ar word
before any substitutions are done on the input line.
Unless a quoting `\e', `"', `\*(aa' or `\*(ga' appears in
.Ar word ,
variable and command substitution is performed on the intervening lines,
allowing `\e' to quote `$', `\e' and `\*(ga'.
Commands that are substituted have all blanks, tabs, and newlines
preserved, except for the final newline which is dropped.
The resultant text is placed in an anonymous temporary file that
is given to the command as its standard input.
.It > name
.It >! name
.It >& name
.It >&! name
The file
.Ar name
is used as the standard output.
If the file does not exist then it is created;
if the file exists, it is truncated; its previous contents are lost.
.Pp
If the variable
.Ar noclobber
is set, then the file must not exist or be a character special file (e.g., a
terminal or `/dev/null') or an error results.
This helps prevent accidental destruction of files.
Here, the `!' forms can be used to suppress this check.
.Pp
The forms involving `&' route the standard error output into the specified
file as well as the standard output.
.Ar Name
is expanded in the same way as `<' input filenames are.
.It >> name
.It >>& name
.It >>! name
.It >>&! name
Uses file
.Ar name
as the standard output;
like `>' but places output at the end of the file.
If the variable
.Ar noclobber
is set, then it is an error for the file not to exist unless
one of the `!' forms is given.
Otherwise similar to `>'.
.El
.Pp
A command receives the environment in which the shell was
invoked as modified by the input-output parameters and
the presence of the command in a pipeline.
Thus, unlike some previous shells, commands run from a file of shell commands
have no access to the text of the commands by default;
instead they receive the original standard input of the shell.
The `<<' mechanism should be used to present inline data.
This permits shell command scripts to function as components of pipelines
and allows the shell to block read its input.
Note that the default standard input for a command run detached is
.Ar not
modified to be the empty file
.Pa /dev/null ;
instead the standard input
remains as the original standard input of the shell.  If this is a terminal
and if the process attempts to read from the terminal, then the process
will block and the user will be notified (see
.Sx Jobs
above).
.Pp
The standard error output may be directed through
a pipe with the standard output.
Simply use the form `\&|&' instead of just `\&|'.
.Ss Expressions
Several of the builtin commands (to be described later)
take expressions, in which the operators are similar to those of C, with
the same precedence.
These expressions appear in the
.Nm @,
.Ar exit ,
.Ar if ,
and
.Ar while
commands.
The following operators are available:
.Bd -ragged -offset indent
\&|\&|  &&  \&| \*(ua  &  ==  !=  =~  !~  <=  >=
<  > <<  >>  +  \-  *  /  %  !  ~  (  )
.Ed
.Pp
Here the precedence increases to the right,
`==' `!=' `=~' and `!~', `<=' `>=' `<' and `>', `<<' and `>>', `+' and `\-',
`*' `/' and `%' being, in groups, at the same level.
The `==' `!=' `=~' and `!~' operators compare their arguments as strings;
all others operate on numbers.
The operators `=~' and `!~' are like `!=' and `==' except that the right
hand side is a
.Ar pattern
(containing, e.g., `*'s, `?'s and instances of `[...]')
against which the left hand operand is matched.  This reduces the
need for use of the
.Ar switch
statement in shell scripts when all that is really needed is pattern matching.
.Pp
Strings that begin with `0' are considered octal numbers.
Null or missing arguments are considered `0'.
The result of all expressions are strings,
which represent decimal numbers.
It is important to note that no two components of an expression can appear
in the same word; except when adjacent to components of expressions that
are syntactically significant to the parser (`&' `\&|' `<' `>' `(' `)'),
they should be surrounded by spaces.
.Pp
Also available in expressions as primitive operands are command executions
enclosed in `{' and `}'
and file enquiries of the form
.Fl l
.Ar name
where
.Ic l
is one of:
.Bd -literal -offset indent
r	read access
w	write access
x	execute access
e	existence
o	ownership
z	zero size
f	plain file
d	directory
.Ed
.Pp
The specified name is command and filename expanded and then tested
to see if it has the specified relationship to the real user.
If the file does not exist or is inaccessible then all enquiries return
false, i.e., `0'.
Command executions succeed, returning true, i.e., `1',
if the command exits with status 0, otherwise they fail, returning
false, i.e., `0'.
If more detailed status information is required then the command
should be executed outside an expression and the variable
.Ar status
examined.
.Ss Control flow
The shell contains several commands that can be used to regulate the
flow of control in command files (shell scripts) and
(in limited but useful ways) from terminal input.
These commands all operate by forcing the shell to reread or skip in its
input and, because of the implementation, restrict the placement of some
of the commands.
.Pp
The
.Ic foreach ,
.Ic switch ,
and
.Ic while
statements, as well as the
.Ic if\-then\-else
form of the
.Ic if
statement require that the major keywords appear in a single simple command
on an input line as shown below.
.Pp
If the shell's input is not seekable,
the shell buffers up input whenever a loop is being read
and performs seeks in this internal buffer to accomplish the rereading
implied by the loop.
(To the extent that this allows, backward goto's will succeed on
non-seekable inputs.)
.Ss Builtin commands
Builtin commands are executed within the shell.
If a builtin command occurs as any component of a pipeline
except the last then it is executed in a subshell.
.Pp
.Bl -tag -width Ds -compact -offset indent
.It Ic alias
.It Ic alias Ar name
.It Ic alias Ar name wordlist
The first form prints all aliases.
The second form prints the alias for name.
The final form assigns the specified
.Ar wordlist
as the alias of
.Ar name ;
.Ar wordlist
is command and filename substituted.
.Ar Name
is not allowed to be
.Ar alias
or
.Ar unalias .
.Pp
.It Ic alloc
Shows the amount of dynamic memory acquired, broken down into used and
free memory.
With an argument shows the number of free and used blocks in each size
category.  The categories start at size 8 and double at each step.
This command's output may vary across system types, since
systems other than the VAX may use a different memory allocator.
.Pp
.It Ic bg
.It Ic bg \&% Ns Ar job ...
Puts the current or specified jobs into the background, continuing them
if they were stopped.
.Pp
.It Ic break
Causes execution to resume after the
.Ic end
of the nearest enclosing
.Ic foreach
or
.Ic while .
The remaining commands on the current line are executed.
Multi-level breaks are thus possible by writing them all on one line.
.Pp
.It Ic breaksw
Causes a break from a
.Ic switch ,
resuming after the
.Ic endsw .
.Pp
.It Ic case Ar label :
A label in a
.Ic switch
statement as discussed below.
.Pp
.It Ic cd
.It Ic cd Ar name
.It Ic chdir
.It Ic chdir Ar name
Change the shell's working directory to directory
.Ar name .
If no argument is given then change to the home directory of the user.
If
.Ar name
is not found as a subdirectory of the current directory (and does not begin
with `/', `./' or `../'), then each
component of the variable
.Ic cdpath
is checked to see if it has a subdirectory
.Ar name .
Finally, if all else fails but
.Ar name
is a shell variable whose value begins with `/', then this
is tried to see if it is a directory.
.Pp
.It Ic continue
Continue execution of the nearest enclosing
.Ic while
or
.Ic foreach .
The rest of the commands on the current line are executed.
.Pp
.It Ic default :
Labels the default case in a
.Ic switch
statement.
The default should come after all
.Ic case
labels.
.Pp
.It Ic dirs
Prints the directory stack; the top of the stack is at the left,
the first directory in the stack being the current directory.
.Pp
.It Ic echo Ar  wordlist
.It Ic echo Fl n Ar wordlist
The specified words are written to the shell's standard output, separated
by spaces, and terminated with a newline unless the
.Fl n
option is specified.
.Pp
.It Ic else
.It Ic end
.It Ic endif
.It Ic endsw
See the description of the
.Ic foreach ,
.Ic if ,
.Ic switch ,
and
.Ic while
statements below.
.Pp
.It Ic eval Ar arg ...
(As in
.Xr sh  1  . )
The arguments are read as input to the shell and the resulting
command(s) executed in the context of the current shell.
This is usually used to execute commands
generated as the result of command or variable substitution, since
parsing occurs before these substitutions.  See
.Xr tset  1
for an example of using
.Ic eval .
.Pp
.It Ic exec Ar command
The specified command is executed in place of the current shell.
.Pp
.It Ic exit
.It Ic exit Ar (expr )
The shell exits either with the value of the
.Ic status
variable (first form) or with the value of the specified
.Ic expr
(second form).
.Pp
.It Ic fg
.It Ic fg % Ns Ar job ...
Brings the current or specified jobs into the foreground, continuing them if
they were stopped.
.Pp
.It Ic foreach Ar name (wordlist)
.It ...
.It Ic end
The variable
.Ic name
is successively set to each member of
.Ic wordlist
and the sequence of commands between this command and the matching
.Ic end
are executed.
(Both
.Ic foreach
and
.Ic end
must appear alone on separate lines.)
The builtin command
.Ic continue
may be used to continue the loop prematurely and the builtin
command
.Ic break
to terminate it prematurely.
When this command is read from the terminal, the loop is read once
prompting with `?' before any statements in the loop are executed.
If you make a mistake typing in a loop at the terminal you can rub it out.
.Pp
.It Ic glob Ar wordlist
Like
.Ic echo
but no `\e' escapes are recognized and words are delimited
by null characters in the output.
Useful for programs that wish to use the shell to filename expand a list
of words.
.Pp
.It Ic goto Ar word
The specified
.Ic word
is filename and command expanded to yield a string of the form `label'.
The shell rewinds its input as much as possible
and searches for a line of the form `label:'
possibly preceded by blanks or tabs.
Execution continues after the specified line.
.Pp
.It Ic hashstat
Print a statistics line showing how effective the internal hash
table has been at locating commands (and avoiding
.Ic exec Ns \'s ) .
An
.Ic exec
is attempted for each component of the
.Em path
where the hash function indicates a possible hit, and in each component
that does not begin with a `/'.
.Pp
.It Ic history
.It Ic history Ar n
.It Ic history Fl r Ar n
.It Ic history Fl h Ar n
Displays the history event list; if
.Ar n
is given only the
.Ar n
most recent events are printed.
The
.Fl r
option reverses the order of printout to be most recent first
instead of oldest first.
The
.Fl h
option causes the history list to be printed without leading numbers.
This format produces files suitable for sourcing using the \-h
option to
.Ic source  .
.Pp
.It Ic if ( Ar expr ) No command
If the specified expression evaluates true, then the single