Provided by: rc_1.7.4+97.gceb59bb-5build2_amd64 
NAME
rc - shell
SYNOPSIS
rc [-deiIlnopsvx] [-c command] [arguments]
DESCRIPTION
rc is a command interpreter and programming language similar to sh(1). It is based on the AT&T Plan 9
shell of the same name. The shell offers a C-like syntax (much more so than the C shell), and a powerful
mechanism for manipulating variables. It is reasonably small and reasonably fast, especially when
compared to contemporary shells. Its use is intended to be interactive, but the language lends itself
well to scripts.
OPTIONS
-c0 If -c0 is present, commands are executed from the immediately following argument. Any further
arguments to rc are placed in $*.0 Thus:
rc -c 'echo $*' 1 2 30
prints out
1 2 30
-d0 This flag causes rc not to ignore SIGQUIT0 or SIGTERM.0 Thus rc can be made to dump core if sent
SIGQUIT.0 This flag is only useful for debugging rc.
-e0 If the -e0 flag is present, then rc will exit if any command fails (exits with non-zero status).
However rc -e does not exit if a conditional fails. A conditional is the test of an if ()0
command, the test of a while ()0 command, or the left hand side of the ||0 or the &&0 operator.
-i0 If the -i0 flag is present or if the input to rc is from a terminal (as determined by isatty(3))
then rc will be in interactive mode. That is, a prompt (from $prompt(1))0 will be printed before
an input line is taken, and rc will ignore SIGINT.0
-I0 If the -I0 flag is present, or if the input to rc is not from a terminal, then rc will not be in
interactive mode. No prompts will be printed, and SIGINT0 will cause rc to exit.
-l0 If the -l0 flag is present, or if rc's argv[0][0]0 is a dash (-),0 then rc will behave as a login
shell. That is, it will run commands from $home/.rcrc,0 if this file exists, before reading any
other input.
-n0 This flag causes rc to read its input and parse it, but not to execute any commands. This is
useful for syntax checking on scripts. If used in combination with the -x0 flag, rc will print
each command as it is parsed in a form similar to the one used for exporting functions into the
environment.
-o0 This flag prevents the usual practice of trying to open /dev/null0 on file descriptors 0, 1, and
2, if any of those descriptors are inherited closed.
-p0 This flag prevents rc from initializing shell functions from the environment. This allows rc to
run in a protected mode, whereby it becomes more difficult for an rc script to be subverted by
placing false commands in the environment. (Note that the presence of this flag does not mean
that it is safe to run setuid rc scripts; the usual caveats about the setuid bit still apply.)
-s0 This flag causes rc to read from standard input. Any arguments are placed in $*.0
-v0 This flag causes rc to echo its input to standard error as it is read.
-x0 This flag causes rc to print every command on standard error before it is executed. It can be
useful for debugging rc scripts.
COMMANDS
A simple command is a sequence of words, separated by white space (space and tab) characters that ends
with a newline, semicolon (;),0 or ampersand (&).0 The first word of a command is the name of that
command. If the name begins with /,0 ./,0 or ../,0 then the name is used as an absolute path name
referring to an executable file. Otherwise, the name of the command is looked up in a table of shell
functions, builtin commands, or as a file in the directories named by $path.0
Background Tasks
A command ending with &0 is run in the background; that is, the shell returns immediately rather than
waiting for the command to complete. Background commands have /dev/null0 connected to their standard
input unless an explicit redirection for standard input is used.
Subshells
A command prefixed with an at-sign (@)0 is executed in a subshell. This insulates the parent shell from
the effects of state changing operations such as a cd or a variable assignment. For example:
@ {cd ..; make}0
will run make(1) in the parent directory (..),0 but leaves the shell running in the current directory.
Line continuation
A long logical line may be continued over several physical lines by terminating each line (except the
last) with a backslash (\).0 The backslash-newline sequence is treated as a space. A backslash is not
otherwise special to rc. (In addition, inside quotes a backslash loses its special meaning even when it
is followed by a newline.)
Quoting
rc interprets several characters specially; special characters automatically terminate words. The
following characters are special:
# ; & | ^ $ ` ' { } ( ) < >0
The single quote (')0 prevents special treatment of any character other than itself. All characters,
including control characters, newlines, and backslashes between two quote characters are treated as an
uninterpreted string. A quote character itself may be quoted by placing two quotes in a row. The
minimal sequence needed to enter the quote character is ''''.0 The empty string is represented by ''.0
Thus:
echo 'What''s the plan, Stan?'0
prints out
What's the plan, Stan?0
The number sign (#)0 begins a comment in rc. All characters up to but not including the next newline are
ignored. Note that backslash continuation does not work inside a comment, i.e., the backslash is ignored
along with everything else.
Grouping
Zero or more commands may be grouped within braces (“{”0 and “}”),0 and are then treated as one command.
Braces do not otherwise define scope; they are used only for command grouping. In particular, be wary of
the command:
for (i) {0
command0
} | command0
Since pipe binds tighter than for,0 this command does not perform what the user expects it to. Instead,
enclose the whole for0 statement in braces:
{for (i) command} | command0
Fortunately, rc's grammar is simple enough that a (confident) user can understand it by examining the
skeletal yacc(1) grammar at the end of this man page (see the section entitled GRAMMAR).
Input and output
The standard output may be redirected to a file with
command > file0
and the standard input may be taken from a file with
command < file0
Redirections can appear anywhere in the line: the word following the redirection symbol is the filename
and must be quoted if it contains spaces or other special characters. These are all equivalent.
echo 1 2 3 > foo0
> foo echo 1 2 30
echo 1 2 > foo 30
File descriptors other than 0 and 1 may be specified also. For example, to redirect standard error to a
file, use:
command >[2] file0
In order to duplicate a file descriptor, use >[n=m].0 Thus to redirect both standard output and standard
error to the same file, use
command > file >[2=1]0
As in sh, redirections are processed from left to right. Thus this sequence
command >[2=1] > file0
is usually a mistake. It first duplicates standard error to standard output; then redirects standard
output to a file, leaving standard error wherever standard output originally was.
To close a file descriptor that may be open, use >[n=].0 For example, to close file descriptor 7:
command >[7=]0
Note that no spaces may appear in these constructs:
command > [2] file0
would send the output of the command to a file named [2],0 with the intended filename appearing in the
command's argument list.
In order to place the output of a command at the end of an already existing file, use:
command >> file0
If the file does not exist, then it is created.
“Here documents” are supported as in sh with the use of
command << 'eof-marker'0
Subsequent lines form the standard input of the command, till a line containing just the marker, in this
case eof-marker,0 is encountered.
If the end-of-file marker is enclosed in quotes, then no variable substitution occurs inside the here
document. Otherwise, every variable is substituted by its space-separated-list value (see Flat Lists,
below), and if a ^0 character follows a variable name, it is deleted. This allows the unambiguous use of
variables adjacent to text, as in
$variable^follow0
To include a literal $0 in a here document when an unquoted end-of-file marker is being used, enter it as
$$.0
Additionally, rc supports “here strings”, which are like here documents, except that input is taken
directly from a string on the command line. Their use is illustrated here:
cat <<< 'this is a here string' | wc0
(This feature enables rc to export functions using here documents into the environment; the author does
not expect users to find this feature useful.)
Pipes
Two or more commands may be combined in a pipeline by placing the vertical bar (|)0 between them. The
standard output (file descriptor 1) of the command on the left is tied to the standard input (file
descriptor 0) of the command on the right. The notation |[n=m]0 indicates that file descriptor n of the
left process is connected to file descriptor m of the right process. |[n]0 is a shorthand for |[n=0].0
As an example, to pipe the standard error of a command to wc(1), use:
command |[2] wc0
As with file redirections, no spaces may occur in the construct specifying numbered file descriptors.
The exit status of a pipeline is considered true if and only if every command in the pipeline exits true.
Commands as Arguments
Some commands, like cmp(1) or diff(1), take their arguments on the command line, and do not read input
from standard input. It is convenient sometimes to build nonlinear pipelines so that a command like cmp
can read the output of two other commands at once. rc does it like this:
cmp <{command} <{command}0
compares the output of the two commands in braces. Note: since this form of redirection is implemented
with some kind of pipe, and since one cannot lseek(2) on a pipe, commands that use lseek(2) will hang.
For example, some versions of diff(1) use lseek(2) on their inputs.
Data can be sent down a pipe to several commands using tee(1) and the output version of this notation:
echo hi there | tee >{sed 's/^/p1 /'} >{sed 's/^/p2 /'}0
CONTROL STRUCTURES
The following may be used for control flow in rc:
If-Else Statements
if (test) {0
cmd
} else cmd0
The test is executed, and if its return status is zero, the first command is executed, otherwise
the second is. Braces are not mandatory around the commands. However, an else0 statement is
valid only if it follows a close-brace on the same line. Otherwise, the if0 is taken to be a
simple-if:
if (test)0
command0
While and For Loops
while (test) cmd0
rc executes the test and performs the command as long as the test is true.
for (var in list) cmd0
rc sets var to each element of list (which may contain variables and backquote substitutions) and
runs cmd. If “in0 list” is omitted, then rc will set var to each element of $*.0 For example:
for (i in `{ls -F | grep '\*$' | sed 's/\*$//'}) { commands }0
will set $i0 to the name of each file in the current directory that is executable.
Switch
switch (list) { case ... }0
rc looks inside the braces after a switch0 for statements beginning with the word case.0 If any of
the patterns following case0 match the list supplied to switch,0 then the commands up until the
next case0 statement are executed. The metacharacters *,0 [0 or ?0 should not be quoted; matching
is performed only against the strings in list, not against file names. (Matching for case
statements is the same as for the ~0 command.)
Logical Operators
There are a number of operators in rc which depend on the exit status of a command.
command && command0
executes the first command and then executes the second command if and only if the first command exits
with a zero exit status (“true” in Unix).
command || command0
executes the first command and then executes the second command if and only if the first command exits
with a nonzero exit status (“false” in Unix).
! command0
negates the exit status of a command.
PATTERN MATCHING
There are two forms of pattern matching in rc. One is traditional shell globbing. This occurs in
matching for file names in argument lists:
command argument argument ...0
When the characters *,0 [0 or ?0 occur in an argument or command, rc looks at the argument as a pattern
for matching against files. (Contrary to the behavior other shells exhibit, rc will only perform pattern
matching if a metacharacter occurs unquoted and literally in the input. Thus,
foo='*'0
echo $foo0
will always echo just a star. In order for non-literal metacharacters to be expanded, an eval0 statement
must be used in order to rescan the input.) Pattern matching occurs according to the following rules: a
*0 matches any number (including zero) of characters. A ?0 matches any single character, and a [0
followed by a number of characters followed by a ]0 matches a single character in that class. The rules
for character class matching are the same as those for ed(1), with the exception that character class
negation is achieved with the tilde (~),0 not the caret (^),0 since the caret already means something
else in rc.
rc also matches patterns against strings with the ~0 command:
~ subject pattern pattern ...0
The ~0 command succeeds (sets $status0 to zero) if and only if one of the patterns0 matches subject.0
Thus
~ foo f*0
succeeds (sets status to zero), while
~ bar f*0
fails (sets status to one).
The null list is matched by the null list, so
~ $foo ()0
checks to see whether $foo0 is empty or not. Because rc does not have hierarchical lists, the test for
emptiness cannot be combined with other tests. To test whether $foo0 is empty, or one of the strings
nada0 or rien,0 do not write
~ $x () nada rien # WRONG means the same as: ~ $x nada rien0
instead write
~ $x () || ~ $x nada rien0
Another way to test if $foo0 is empty is
~ $#foo 00
Note that inside a ~0 command rc does not match patterns against file names, so it is not necessary to
quote the characters *,0 [0 and ?.0 However, rc does expand the subject against filenames if it contains
metacharacters. Thus, the command
~ * ?0
succeeds if any of the files in the current directory have a single-character name.
If the ~0 command is given a list as its first argument, then a successful match against any of the
elements of that list will cause ~0 to succeed. For example:
~ (foo goo zoo) z*0
is true.
LISTS AND VARIABLES
The primary data structure in rc is the list, which is a sequence of words. Parentheses are used to
group lists. The empty list is represented by ().0 Lists have no hierarchical structure; a list inside
another list is expanded so the outer list contains all the elements of the inner list. Thus, the
following are all equivalent
one two three0
(one two three)0
((one) () ((two three)))0
Note that the null string, '',0 and the null list, (),0 are two very different things. Assigning the
null string to a variable is a valid operation, but it does not remove its definition.
null = '' empty = () echo $#null $#empty0
produces the output
1 00
List Concatenation
Two lists may be joined by the concatenation operator (^).0 Concatenation works according to the
following rules: if the two lists have the same number of elements, then concatenation is pairwise:
echo (a- b- c-)^(1 2 3)0
produces the output
a-1 b-2 c-30
Otherwise, at least one of the lists must have a single element, and then the concatenation is
distributive:
cc -^(O g c) (malloc alloca)^.c0
has the effect of performing the command
cc -O -g -c malloc.c alloca.c0
A single word is a list of length one, so
echo foo^bar0
produces the output
foobar0
Free Carets
rc inserts carets (concatenation operators) for free in certain situations, in order to save some typing
on the user's behalf. For example, the above example could also be typed in as:
opts=(O g c) files=(malloc alloca) cc -$opts $files.c0
rc takes care to insert a free caret between the ``-''0 and $opts,0 as well as between $files0 and .c.0
The rule for free carets is as follows: if a word or keyword is immediately followed by another word,
keyword, dollar-sign or backquote, then rc inserts a caret between them.
Variables
A list may be assigned to a variable, using the notation:
var = list0
The special variable *0 may also be assigned to using this notation; rc has no set builtin.
Any non-empty sequence of characters, except a sequence including only digits, may be used as a variable
name. Any character except =0 may be used, but special characters must be quoted. All user-defined
variables are exported into the environment.
The value of a variable is referenced with the dollar ($)0 operator:
$var0
Any variable which has not been assigned a value returns the null list, (),0 when referenced. Multiple
references are allowed:
a = foo0
b = a0
echo $ $ b0
prints
foo0
A variable's definition may also be removed by assigning the null list to a variable:
var=()0
For “free careting” to work correctly, rc must make certain assumptions about what characters may appear
in a variable name. rc assumes that a variable name consists only of alphanumeric characters, underscore
(_)0 and star (*).0 To reference a variable with other characters in its name, quote the variable name.
Thus:
echo $'we$Ird:Variab!le'0
Local Variables
Any number of variable assignments may be made local to a single command by typing:
a=foo b=bar ... command0
The command may be a compound command, so for example:
path=. ifs=() {0
...0
}0
sets path0 to .0 and removes ifs0 for the duration of one long compound command.
Variable Subscripts
Variables may be subscripted with the notation
$var(n)0
where n is a list of integers (origin 1). The opening parenthesis must immediately follow the variable
name. The list of subscripts need not be in order or even unique. Thus,
a=(one two three)0
echo $a(3 3 3)0
prints
three three three0
If n references a nonexistent element, then $var(n)0 returns the null list. The notation $n,0 where n is
an integer, is a shorthand for $*(n).0 Thus, rc's arguments may be referred to as $1,0 $2,0 and so on.
Note also that the list of subscripts may be given by any of rc's list operations:
$var(`{awk 'BEGIN{for(i=1;i<=10;i++)print i;exit; }'})0
returns the first 10 elements of $var.0
To count the number of elements in a variable, use
$#var0
This returns a single-element list, with the number of elements in $var.0
Flat Lists
In order to create a single-element list from a multi-element list, with the components space-separated,
use the dollar-caret ($^)0 operator:
$^var0
This is useful when the normal list concatenation rules need to be bypassed. For example, to append a
single period at the end of $path,0 use:
echo $^path.0
For compatibility with the Plan 9 rc,
$"var0
is accepted as a synonym for dollar-caret.
Backquote Substitution
A list may be formed from the output of a command by using backquote substitution:
`{ command }0
returns a list formed from the standard output of the command in braces. $ifs0 is used to split the
output into list elements. By default, $ifs0 has the value space-tab-newline.
The braces may be omitted if the command is a single word. Thus `ls0 may be used instead of `{ls}.0 This
last feature can be used to create shortcuts by defining functions that expand to useful argument lists.
For example:
fn src { echo *.[chy] }0
followed by
wc `src0
This will print out a word-count of all C source files in the current directory.
In order to override the value of $ifs0 for a single backquote substitution, use:
`` (ifs-list) { command }0
$ifs0 will be temporarily ignored and the command's output will be split as specified by the list
following the double backquote. For example:
`` ($nl :) {cat /etc/passwd}0
splits up /etc/passwd0 into fields.
As a convenience, rc defines $nl0 to contain the newline character, and $tab0 to contain the tab
character. Thus, if you want to process everything in the current directory, but in a random order, you
could use:
for (f in `` $nl {ls | shuf}) { ... process $f }0
This will correctly handle filenames that contain spaces.
Note that rc scripts that use backquote substitution should avoid relying on the default values of $ifs,0
$nl,0 or $tab.0 Instead, they should explicitly set what they need.
SPECIAL VARIABLES
Several variables are known to rc and are treated specially. In the following list, “default” indicates
that rc gives the variable a default value on startup; “no-export” indicates that the variable is never
exported; and “read-only” indicates that an attempt to set the variable will silently have no effect.
Also, “alias” means that the variable is aliased to the same name in capitals. For example, an
assignment to $cdpath0 causes an automatic assignment to $CDPATH,0 and vice-versa. If $CDPATH0 is set
when rc is started, its value is imported into $cdpath.0 $cdpath0 and $path0 are rc lists; $CDPATH0 and
$PATH0 are colon-separated lists. Only the names spelt in capitals are exported into the environment.
* (no-export)0
The argument list of rc. $1, $2,0 etc. are the same as $*(1),0 $*(2),0 etc.
0 (default no-export)0
The variable $00 holds the value of argv[0]0 with which rc was invoked. Additionally, $00 is set
to the name of a function for the duration of the execution of that function, and $00 is also set
to the name of the file being interpreted for the duration of a .0 command. $00 is not an element
of $*,0 and is never treated as one.
apid (no-export)0
The process ID of the last process started in the background.
apids (no-export read-only)0
A list whose elements are the process IDs of all background processes which are still alive, or
which have died and have not been waited for yet.
bqstatus (no-export)0
The exit status of the rc forked to execute the most recent backquote substitution. Note that,
unlike $status,0 $bqstatus0 is always a single element list (see EXIT STATUS below). For example:
echo foo |grep bar; whatis status0
prints
status=(0 1)0
whereas
x=`{echo foo |grep bar}; whatis bqstatus0
prints
bqstatus=10
cdpath (alias)0
A list of directories to search for the target of a cd command. The empty string stands for the
current directory. Note that if the $cdpath0 variable does not contain the current directory,
then the current directory will not be searched; this allows directory searching to begin in a
directory other than the current directory.
history0
$history0 contains the name of a file to which commands are appended as rc reads them. This
facilitates the use of a stand-alone history program (such as history(1)) which parses the
contents of the history file and presents them to rc for reinterpretation. If $history0 is not
set, then rc does not append commands to any file.
home (alias)0
The default directory for the builtin cd command, and the directory in which rc looks to find its
initialization file, .rcrc,0 if rc has been started up as a login shell.
ifs (default)0
The internal field separator, used for splitting up the output of backquote commands for digestion
as a list. On startup, rc assigns the list containing the characters space, tab, and newline to
$ifs.0
nl (default)0
Contains the newline character (see Backquote substitution above).
path (alias)0
This is a list of directories to search in for commands. The empty string stands for the current
directory. If neither $PATH0 nor $path0 is set at startup time, $path0 assumes a default value
suitable for your system. This is typically (/usr/local/bin /usr/bin /usr/ucb /bin .)0
pid (default no-export)0
On startup, $pid0 is initialized to the numeric process ID of the currently running rc.
prompt (default)0
This variable holds the two prompts (in list form, of course) that rc prints. $prompt(1)0 is
printed before each command is read, and $prompt(2)0 is printed when input is expected to continue
on the next line. rc sets $prompt0 to ('; ' '')0 by default. The reason for this is that it
enables an rc user to grab commands from previous lines using a mouse, and to present them to rc
for re-interpretation; the semicolon prompt is simply ignored by rc. The null $prompt(2)0 also
has its justification: an rc script, when typed interactively, will not leave $prompt(2)'s0 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.
prompt (function)0
If this function is defined, then it gets executed every time rc is about to print $prompt(1).0
status (no-export read-only)0
The exit status of the last command. If the command exited with a numeric value, that number is
the status. If the command died with a signal, the status is the name of that signal; if a core
file was created, the string “+core”0 is appended. The value of $status0 for a pipeline is a
list, with one entry, as above, for each process in the pipeline. For example, the command
ls | wc0
usually sets $status0 to (0 0).0
tab (default)0
Contains the tab character (see Backquote substitution above).
version (default)0
On startup, the first element of this list variable is initialized to a string which identifies
this version of rc. The second element is initialized to a string which can be found by ident(1)
and the what command of sccs(1).
FUNCTIONS
rc functions are identical to rc scripts, except that they are stored in memory and are automatically
exported into the environment. A shell function is declared as:
fn name { commands }0
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
fn name0
(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, $*0 is set to the arguments
to that function for the duration of the command. Thus a reasonable definition for l,0 a shorthand for
ls(1), could be:
fn l { ls -FC $* }0
but not
fn l { ls -FC } # WRONG0
INTERRUPTS AND SIGNALS
rc recognizes a number of signals, and allows the user to define shell functions which act as signal
handlers. rc by default traps SIGINT0 when it is in interactive mode. SIGQUIT0 and SIGTERM0 are
ignored, unless rc has been invoked with the -d0 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:
fn sighup { echo hangup; rm /tmp/rc$pid.*; exit }0
In addition to Unix signals, rc recognizes the artificial signal SIGEXIT0 which occurs as rc is about to
exit.
In order to remove a signal handler's definition, remove it as though it were a regular function. For
example:
fn sigint0
returns the handler of SIGINT0 to the default value. In order to ignore a signal, set the signal
handler's value to {}.0 Thus:
fn sigint {}0
causes SIGINT0 to be ignored by the shell. Only signals that are being ignored are passed on to programs
run by rc; signal functions are not exported.
On System V-based Unix systems, rc will not allow you to trap SIGCLD.0
BUILTIN COMMANDS
Builtin commands execute in the context of the shell, but otherwise behave exactly like other commands.
Although !, ~ and @ are not strictly speaking builtin commands, they can usually be used as such.
. [-i] file [arg ...]
Reads file as input to rc and executes its contents. With a -i0 flag, input is interactive. Thus
from within a shell script,
. -i /dev/tty0
does the “right thing”.
break Breaks from the innermost for0 or while,0 as in C. It is an error to invoke break outside of a
loop. (Note that there is no break keyword between commands in switch0 statements, unlike C.)
builtin command [arg ...]
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. For
example:
fn ls { builtin ls -FC $* }0
is a reasonable way to pass a default set of arguments to ls(1),0 whereas
fn ls { ls -FC $* } # WRONG0
is a non-terminating recursion, which will cause rc0 to exhaust its stack space and (eventually)
terminate if it is executed.
cd [directory]
Changes the current directory to directory. The variable $cdpath0 is searched for possible
locations of directory, analogous to the searching of $path0 for executable files. With no
argument, cd changes the current directory to $home.0
continue
Continues the innermost for0 or while0 loop, as in C. It is an error to invoke continue outside
of a loop.
echo [-n] [--] [arg ...]
Prints its arguments to standard output, terminated by a newline. Arguments are separated by
spaces. If the first argument is -n0 no final newline is printed. If the first argument is --,0
then all other arguments are echoed literally. This is used for echoing a literal -n.0
eval [list]
Concatenates the elements of list with spaces and feeds the resulting string to rc for re-
scanning. This is the only time input is rescanned in rc.
exec [arg ...]
Replaces 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,
exec >[2] err.out0
places further output to standard error in the file err.out.
exit [status]
Cause the current shell to exit with the given exit status. If no argument is given, the current
value of $status0 is used.
flag f [ + | - ]
Test, set (+), or reset (-) command-line flag f. For example, a script that requires ``exit if
command fails'' semantics can say
flag e +0
Some flags cannot be set or reset using flag, but they can still be tested. These are c, d, l, o,
p, and s. As a special case, flag i0 operates on rc's internal interactive flag, which may have
been set by -i0 on the command line, or if standard input was a terminal; there is no flag I.0
limit [-h] [resource [value]]
Similar to the csh(1) limit builtin, this command operates upon the BSD-style resource limits of a
process. The -h0 flag displays/alters the hard limits. The resources which can be shown or
altered are cputime, filesize, datasize, stacksize, coredumpsize, memoryuse, and, where supported,
descriptors, memoryuse, memoryrss, maxproc, memorylocked, and filelocks. For example:
limit coredumpsize 00
disables core dumps. To set a soft limit equal to the hard limit:
limit `{limit -h datasize}0
newpgrp
Puts rc into a new process group. This builtin is useful for making 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.
return [n]
Returns from the current function, with status n, where n is a valid exit status, or a list of
them. Thus it is legal to have
return (sigpipe 1 2 3)0
(This is commonly used to allow a function to return with the exit status of a previously executed
pipeline of commands.) If n is omitted, then $status0 is left unchanged. It is an error to
invoke return when not inside a function.
shift [n]
Deletes n elements from the beginning of $*0 and shifts the other elements down by n. n defaults
to 1.
umask [mask]
Sets the current umask (see umask(2)) to the octal mask. If no argument is present, the current
mask value is printed.
wait [pid]
Waits for process with the specified pid, which must have been started by rc, to exit. If no pid
is specified, rc waits for all its child processes to exit.
whatis [-b] [-f] [-p] [-s] [-v] [--] [name ...]
Prints a definition of the named objects. For builtins, builtin0 foo is printed; for functions,
including signal handlers, their definitions are printed; for executable files, path names are
printed; and for variables, their values are printed. The flags restrict output to builtins,
functions, executable programs, signal handlers, and variables, respectively. If no names are
specified, rc lists all objects of that type. (This is not permitted for -p.)0 Without arguments,
whatis0 is equivalent to whatis -fv,0 and prints the values of all shell variables and functions.
Note that whatis output is suitable for input to rc; by saving the output of whatis in a file, it
should be possible to recreate the state of rc by sourcing this file with a .0 command. Another
note: whatis -s > file0 cannot be used to store the state of rc's signal handlers in a file,
because builtins with redirections are run in a subshell, and rc always restores signal handlers
to their default value after a fork().0
Since whatis uses getopt(3) to parse its arguments, you can use the special argument --0 to
terminate its flags. This allows you to use names beginning with a dash, such as the history(1)
commands. For example,
whatis -- -p0
EXAMPLES
The shift builtin only shifts $*.0 This function can shift any variable (except $_lshift).0
fn lshift { _lshift=$* *=$$1 { shift $_lshift(2); $_lshift(1)=$* } }0
With this definition in place,
walrus = (shoes ships sealing-wax cabbages kings)0
lshift walrus 30
whatis walrus0
prints
walrus=(cabbages kings)0
The $^var0 operator flattens a list by separating each element with a space. This function allows the
separator to be an arbitrary string.
fn lflat {0
lflat=$*; *=$$10
while () {0
echo -n $1; shift0
~ $#* 0 && break0
echo -n $lflat(2)0
}0
}0
With this definition in place,
hops=(uunet mcvax ukc tlg)0
lflat hops !0
prints (with no final newline)
uunet!mcvax!ukc!tlg0
EXIT STATUS
The exit status of rc is normally the same as that of the last command executed. If the last command was
a pipeline, rc exits 00 if every command in the pipeline did; otherwise it exits 1.0
rc can be made to exit with a particular status using the exit builtin.
LINE EDITING
rc is typically built against a line editing library. On GNU/Linux systems this will usually be the GNU
readline library. On *BSD systems it is more likely to be the BSD editline library. Please consult the
appropriate library documentation for details of how to use and configure line editing.
Tilde Expansion
Since rc does not support tilde expansion (converting ~foo0 to the home directory of user foo),0 it is
sometimes suggested by users as a possible enhancement. The authors and maintainers of rc have a proud
history of resisting such feature requests. So it is worth noting here that GNU readline can expand
tildes. Add this line to the file .inputrc0 in your home directory.
set expand-tilde on0
and then use the key sequence M-~0 to perform tilde expansion on the current word. See the readline
documentation for further details.
GRAMMAR
Here is rc's grammar, edited to remove semantic actions.
%term ANDAND BACKBACK BANG CASE COUNT DUP ELSE END FLAT FN FOR IF IN
%term OROR PIPE REDIR SUB SUBSHELL SWITCH TWIDDLE WHILE WORD HUH
%left '^' '='
%left WHILE ')' ELSE
%left ANDAND OROR '\n'
%left BANG SUBSHELL
%left PIPE
%right '$'
%left SUB
%start rc
%%
rc: line end
| error end
end: END /* EOF */ | '\n'
cmdsa: cmd ';' | cmd '&'
line: cmd | cmdsa line
body: cmd | cmdsan body
cmdsan: cmdsa | cmd '\n'
brace: '{' body '}'
paren: '(' body ')'
assign: first optcaret '=' optcaret word
epilog: /* empty */ | redir epilog
redir: DUP | REDIR word
case: CASE words ';' | CASE words '\n'
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 */ %prec '^' | '^'
simple: first | first args
args: arg | args arg
arg: word | 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 '\n'
FILES
$HOME/.rcrc,0 /tmp/rc*,0 /dev/null0
CREDITS
rc was written by Byron Rakitzis, with valuable help from Paul Haahr, Hugh Redelmeier and David
Sanderson. The design of this shell was copied from the rc that Tom Duff wrote at Bell Labs.
BUGS
There is a compile-time limit on the number of ;0 separated commands in a line: usually 500. This is
sometimes a problem for automatically generated scripts: substituting the newline character for ;0 avoids
the limit.
On modern systems that support /dev/fd0 or /proc/self/fd,0 <{foo}0 style redirection is implemented that
way. However, on older systems it is implemented with named pipes. Allegedly, it is sometimes possible
to foil rc into removing the FIFO it places in /tmp0 prematurely, or it is even possible to cause rc to
hang. (The current maintainer has never seen this, but then he doesn't use systems which lack /dev/fd0
any more. If anybody can reproduce this problem, please let the maintainer know.)
The echo command does not need to be a builtin. It is one for reasons of performance and portability (of
rc scripts).
There should be a way to avoid exporting a variable.
Extra parentheses around a ~0 expression or a !0 expression are a syntax error. Thus, this code is
illegal.
while ((~ $1 -*) && (! ~ $1 --)) { ...0
The redundant inner parentheses must be omitted.
Variable subscripting cannot be used in here documents.
The limit0 builtin silently ignores extra arguments.
Backquote substitution never produces empty strings - multiple consecutive occurrences of the separator
are treated the same as a single occurrence.
ifs=! { x = `{echo -n a!!b}; whatis x }0
x=(a b) # NOT x=(a '' b)0
Bug reports should be mailed to
<toby@paccrat.org>.0
INCOMPATIBILITIES
Here is a list of features which distinguish this incarnation of rc from the one described in the Bell
Labs manual pages:
The Tenth Edition rc does not have the else keyword. Instead, if is optionally followed by an if not
clause which is executed if the preceding if test does not succeed.
Backquotes are slightly different in Tenth Edition rc: a backquote must always be followed by a left-
brace. This restriction is not present for single-word commands in this rc.
For .0 file, the Tenth Edition rc searches $path0 for file. This rc does not, since it is not considered
useful.
The list flattening operator, $^foo,0 is spelt $"foo0 in those versions of the Bell Labs rc which have
it.
The following are all new with this version of rc: The -n0 flag, here strings (they facilitate exporting
of functions with here documents into the environment), the return and break keywords, the echo builtin,
the bqstatus0 and version0 variables, the prompt0 function, support for GNU readline and other line
editing libraries. This rc also sets $00 to the name of a function being executed/file being sourced.
SEE ALSO
“rc — A Shell for Plan 9 and UNIX Systems”, Unix Research System, Tenth Edition, Volume 2. (Saunders
College Publishing)
http://static.tobold.org/rc/rc-duff.html,0 an updated version of the above paper.
history(1)
2015-05-13 RC(1)