rc.1

早期freebsd实现

by default.
The reason for this is that it enables an
.I rc
user to grab commands from previous lines using a
mouse, and to present them to
.I rc
for re-interpretation; the semicolon
prompt is simply ignored by
.IR rc .
The null
.Cr $prompt(2)
also has its
justification:  an
.I rc
script, when typed interactively, will not leave
.Cr $prompt(2) 's
on the screen,
and can therefore be grabbed by a mouse and placed
directly into a file for use as a shell script, without further editing
being necessary.
.TP
.Cr prompt " (function)"
If this function is set, then it gets executed every time
.I rc
is about to print
.Cr "$prompt(1)" .
.TP
.Cr status
The exit status of the last command.
If the command exited with a numeric value,
that number is the status.
If the died with a signal,
the status is the name of that signal; if a core file
was created, the string
.Rc `` +core ''
is appended.
The value of
.Cr $status
for a pipeline is a list, with one entry,
as above, for each process in the pipeline.
For example, the command
.Ds
.Cr "ls | wc"
.De
.TP
\&
usually sets
.Cr $status
to
.Cr "(0 0)" .
.PP
The values of
.Cr "$path" ,
.Cr "$cdpath" ,
and
.Cr $home
are derived from the environment
values of
.Cr "$PATH" ,
.Cr "$CDPATH" ,
and
.Cr "$HOME" .
Otherwise, they are derived from
the environment values of
.Cr $path ,
.Cr $cdpath
and
.Cr $home .
This is for compatibility with other Unix programs, like
.IR sh (1).
.Cr $PATH
and
.Cr $CDPATH
are assumed to be colon-separated lists.
.SH FUNCTIONS
.I rc
functions are identical to
.I rc
scripts, except that they are stored
in memory and are automatically exported into the environment.
A shell function is declared as:
.Ds
.Cr "fn name { commands }"
.De
.PP
.I rc
scans the definition until the close-brace, so the function can
span more than one line.
The function definition may be removed by typing
.Ds
.Cr "fn name"
.De
.PP
(One or more names may be specified.
With an accompanying definition, all names receive the same definition.
This is sometimes useful
for assigning the same signal handler to many signals.
Without a definition, all named functions are deleted.)
When a function is executed,
.Cr $*
is set to the arguments to that
function for the duration of the command.
Thus a reasonable definition for
.Cr "l" ,
a shorthand for
.IR ls (1),
could be:
.Ds
.Cr "fn l { ls -FC $* }"
.De
.PP
but not
.Ds
.Cr "fn l { ls -FC }"
.De
.SH "INTERRUPTS AND SIGNALS"
.I rc
recognizes a number of signals, and allows the user to define shell
functions which act as signal handlers.
.I rc
by default traps
.Cr SIGINT
when it is in interactive mode.
.Cr SIGQUIT
and
.Cr SIGTERM
are ignored, unless
.I rc
has been invoked with the
.Cr \-d
flag.
However, user-defined signal handlers may be written for these and
all other signals.
The way to define a signal handler is to
write a function by the name of the signal in lower case.
Thus:
.Ds
.Cr "fn sighup { echo hangup; rm /tmp/rc$pid.*; exit }"
.De
.PP
In addition to Unix signals,
.I rc
recognizes the artificial signal
.Cr SIGEXIT
which occurs as
.I rc
is about to exit.
.PP
In order to remove a signal handler's definition,
remove it as though it were a regular function.
For example:
.Ds
.Cr "fn sigint"
.De
.PP
returns the handler of
.Cr SIGINT
to the default value.
In order to ignore a signal, set the signal handler's value to
.Cr "{}" .
Thus:
.Ds
.Cr "fn sigint {}"
.De
.PP
causes SIGINT to be ignored by the shell.
Only signals that are being ignored are passed on to programs run by
.IR rc ;
signal functions are not exported.
.PP
On System V-based Unix systems,
.I rc
will not allow you to trap
.Cr SIGCLD .
.SH "BUILTIN COMMANDS"
Builtin commands execute in the context of the shell, but otherwise
behave exactly like other commands.
Although
.BR ! ,
.B ~
and
.B @
are not strictly speaking builtin commands,
they can usually be used as such.
.TP
\&\fB.\fR [\fB\-i\fR] \fIfile \fR[\fIarg ...\fR]
Reads
.I file
as input to
.IR rc
and executes its contents.
With a
.Cr \-i
flag, input is interactive.
Thus from within a shell script,
.Ds
.Cr ". \-i /dev/tty"
.De
.TP
\&
does the ``right'' thing.
.TP
.B break
Breaks from the innermost
.Cr for
or
.Cr while ,
as in C.
It is an error to invoke
.B break
outside of a loop.
(Note that there is no
.B break
keyword between commands in
.Cr switch
statements, unlike C.)
.TP
\fBbuiltin \fIcommand \fR[\fIarg ...\fR]
Executes the command ignoring any function definition of the
same name.
This command is present to allow functions with the
same names as builtins to use the underlying builtin or binary.
.TP
\fBcd \fR[\fIdirectory\fR]
Changes the current directory to
.IR directory .
The variable
.Cr $cdpath
is searched for possible locations of
.IR directory ,
analogous to the searching of
.Cr $path
for executable files.
With no argument,
.B cd
changes the current directory to
.Cr "$home" .
.TP
\fBecho \fR[\fB\-n\fR] [\fB\-\|\-\fR] [\fIarg ...\fR]
Prints its arguments to standard output, terminated by a newline.
Arguments are separated by spaces.
If the first argument is
.Cr "\-n"
no final newline is printed.
If the first argument is
.Cr "\-\|\-" ,
then all other arguments are echoed literally.
This is used for echoing a literal
.Cr "\-n" .
.TP
\fBeval \fR[\fIlist\fR]
Concatenates the elements of
.I list
with spaces and feeds the resulting string to
.I rc
for re-scanning.
This is the only time input is rescanned in
.IR rc .
.TP
\fBexec \fR[\fIarg ...\fR]
Replaces
.I rc
with the given command.
If the exec contains only redirections,
then these redirections apply to the current shell
and the shell does not exit.
For example,
.Ds
.Cr "exec >[2] err.out"
.De
.TP
\&
places further output to standard error in the file
.IR err.out .
.TP
\fBexit \fR[\fIstatus\fR]
Cause the current shell to exit with the given exit
.IR status .
If no argument is given, the current value of
.Cr $status
is used.
.TP
\fBlimit \fR[\fB\-h\fR] [\fIresource \fR[\fIvalue\fR]]
Similar to the
.IR csh (1)
.B limit
builtin, this command operates upon the
BSD-style limits of a process.
The
.Cr \-h
flag displays/alters the hard
limits.
The resources which can be shown or altered are
.BR cputime ,
.BR filesize ,
.BR datasize ,
.BR stacksize ,
.B coredumpsize
and
.BR memoryuse .
For
example:
.Ds
.Cr "limit coredumpsize 0"
.De
.TP
\&
disables core dumps.
.TP
.B newpgrp
Puts
.I rc
into a new process group.
This builtin is useful for making
.I rc
behave like a job-control shell in a hostile environment.
One example is the NeXT Terminal program, which implicitly assumes
that each shell it forks will put itself into a new process group.
.TP
\fBreturn \fR[\fIn\fR]
Returns from the current function, with status
.IR n ,
where
.IR n
is a single value or a list of possible exit statuses.
Thus it is legal to have
.Ds
.Cr "return (sigpipe 1 2 3)"
.De
.TP
\&
(This is commonly used to allow a function to return with the exit status
of a previously executed pipeline of commands.)
If
.IR n
is omitted, then
.Cr $status
is left unchanged.
It is an error to invoke
.B return
when not inside a function.
.TP
\fBshift \fR[\fIn\fR]
Deletes
.I n
elements from the beginning of
.Cr $*
and shifts the other
elements down by
.IR n .
.I n
defaults to 1.
(Note that
.Cr $0
is not affected by
.BR shift .)
.TP
\fBumask \fR[\fImask\fR]
Sets the current umask (see
.IR umask (2))
to the octal
.IR mask .
If no argument is present, the current mask value is printed.
.TP
\fBwait \fR[\fIpid\fR]
Waits for the specified
.IR pid ,
which must have been started by
.IR rc .
If no
.I pid
is specified,
.I rc
waits for any child process to exit.
.TP
\fBwhatis \fR[\fB\-s\fR] [\fB\-\|\-\fR] [\fIname ...\fR]
Prints a definition of the named objects.
For variables, their values
are printed; for functions, their definitions are; and for executable
files, path names are printed.
Without arguments,
.B whatis
prints the values of all shell variables and functions.
With a
.Cr \-s
argument,
.B whatis
also prints out a list of available signals and their handlers (if any).
Note that
.B whatis
output is suitable for input to
.IR rc ;
by saving the output of
.B whatis
in a file, it should be possible to recreate the state of
.I rc
by sourcing this file with a
.Cr .
command.
Another note:
.Cr "whatis -s > file"
cannot be used to store the state of
.IR rc 's
signal handlers in a file, because builtins with redirections
are run in a subshell, and
.I rc
always restores signal handlers to their default value after a
.Cr fork() .
.TP
\&
Since
.B whatis
uses
.IR getopt (3)
to parse its arguments, you can use the special argument
.Cr "\-\|\-"
to terminate its options.
This allows you to use names beginning with a dash, such as
the
.IR history (1)
commands.
For example,
.Ds
.Cr "whatis \-\|\- \-p"
.De
.SH GRAMMAR
Here is
.IR rc 's
grammar, edited to remove semantic actions.
.Ds
.ft \*(Cf
%term ANDAND BACKBACK BANG CASE COUNT DUP ELSE END FLAT FN FOR IF IN
%term OROR PIPE REDIR SUB SUBSHELL SWITCH TWIDDLE WHILE WORD HUH

%left WHILE ')' ELSE
%left ANDAND OROR '\en'
%left BANG SUBSHELL
%left PIPE
%right '$'
%left SUB

%start rc

%%

rc: line end
	| error end

end: END /* EOF */ | '\en'

cmdsa: cmd ';' | cmd '&'

line: cmd | cmdsa line

body: cmd | cmdsan body

cmdsan: cmdsa | cmd '\en'

brace: '{' body '}'

paren: '(' body ')'

assign: first '=' word

epilog: /* empty */ | redir epilog

redir: DUP | REDIR word

case: CASE words ';' | CASE words '\en'

cbody: cmd | case cbody | cmdsan cbody

iftail: cmd	%prec ELSE
	| brace ELSE optnl cmd

cmd	: /* empty */	%prec WHILE
	| simple
	| brace epilog
	| IF paren optnl iftail
	| FOR '(' word IN words ')' optnl cmd
	| FOR '(' word ')' optnl cmd
	| WHILE paren optnl cmd	
	| SWITCH '(' word ')' optnl '{' cbody '}'
	| TWIDDLE optcaret word words
	| cmd ANDAND optnl cmd
	| cmd OROR optnl cmd
 	| cmd PIPE optnl cmd
	| redir cmd	%prec BANG
	| assign cmd	%prec BANG
	| BANG optcaret cmd
	| SUBSHELL optcaret cmd
	| FN words brace
	| FN words

optcaret: /* empty */ | '^'

simple: first | simple word | simple redir

first: comword | first '^' sword

sword: comword | keyword

word: sword | word '^' sword

comword: '$' sword
	| '$' sword SUB words ')'
	| COUNT sword
	| FLAT sword
	| '`' sword
	| '`' brace
	| BACKBACK word	brace | BACKBACK word sword
	| '(' words ')'
	| REDIR brace
	| WORD

keyword: FOR | IN | WHILE | IF | SWITCH
	| FN | ELSE | CASE | TWIDDLE | BANG | SUBSHELL

words: /* empty */ | words word

optnl: /* empty */ | optnl '\en'
.ft R
.De
.SH FILES
.Cr $HOME/.rcrc ,
.Cr /tmp/rc* ,
.Cr /dev/null
.SH CREDITS
.I rc
was written by Byron Rakitzis, with valuable help
from Paul Haahr, Hugh Redelmeier and David Sanderson.
The design of this shell has been copied from the
.I rc
that Tom Duff wrote at Bell Labs.
.SH BUGS
On systems that support
.Cr /dev/fd ,
.Cr <{foo}
style redirection is implemented that way.
However, on other systems it is implemented with named pipes,
and it is sometimes
possible to foil
.I rc
into removing the FIFO it places in
.Cr /tmp
prematurely, or it is even possible to cause
.I rc
to hang.
.PP
The functionality of
.B shift
should be available for variables other than
.Cr "$*" .
.PP
.B echo
is built in only for performance reasons, which is a bad idea.
.PP
There should be a way to avoid exporting a variable.
.PP
The
.Cr $^var
notation for flattening should allow for using an arbitrary
separating character, not just space.
.PP
Bug reports should be mailed to
.Cr "[e-mail]" .
.SH INCOMPATIBILITIES
Here is a list of features which distinguish this incarnation of
.I rc
from the one described in the Bell Labs manual pages:
.PP
The treatment of
.Cr if - else
is different in the v10
.IR rc :
that version uses an
.Cr "if not"
clause which gets executed
if the preceding
.Cr if
test does not succeed.
.PP
Backquotes are slightly different in v10
.IR rc :
a backquote must always be followed by a left-brace.
This restriction is not present for single-word commands in this
.IR rc .
.PP
The following are all new with this version of
.IR rc :
The
.Cr \-n
option,
the list flattening operator,
here strings (they facilitate exporting of functions
with here documents into the environment),
the
.B return
and
.B break
keywords,
the
.B echo
builtin,
the support for the GNU
.IR readline (3)
library and
the support for the
.Cr prompt
function.
This
.I rc
also sets
.Cr $0
to the name of a function being executed/file
being sourced.
.SH "SEE ALSO"
``rc \(em A Shell for Plan 9 and UNIX Systems'',
Unix Research System,
10th Edition,
vol. 2. (Saunders College Publishing)
(This paper is also distributed with this
.I rc
in PostScript form.)
.PP
.IR history (1)