rc.1

.\" rc.1
.\"-------
.\" Man page portability notes
.\"
.\" These are some notes on conventions to maintain for greatest
.\" portability of this man page to various other versions of
.\" nroff.
.\"
.\" When you want a \ to appear in the output, use \e in the man page.
.\" (NOTE this comes up in the rc grammar, where to print out '\n' the
.\" man page must contain '\en'.)
.\"
.\" Evidently not all versions of nroff allow the omission of the
.\" terminal " on a macro argument. Thus what could be written
.\"
.\" .Cr "exec >[2] err.out
.\"
.\" in true nroffs must be written
.\"
.\" .Cr "exec >[2] err.out"
.\"
.\" instead.
.\"
.\" Use symbolic font names (e.g. R, I, B) instead of the standard
.\" font positions 1, 2, 3. Note that for Xf to work the standard
.\" font names must be single characters.
.\"
.\" Not all man macros have the RS and RE requests (I altered the Ds
.\" and De macros and the calls to Ds accordingly).
.\"
.\" Thanks to Michael Haardt (u31b3hs@cip-s01.informatik.rwth-aachen.de)
.\" for pointing out these problems.
.\"
.\" Note that sentences should end at the end of a line. nroff and
.\" troff will supply the correct inter-sentence spacing, but only if
.\" the sentences end at the end of a line. Explicit spaces, if given,
.\" are apparently honored and the normal inter-sentence spacing is
.\" suppressed.
.\"
.\" DaviD W. Sanderson
.\"-------
.\" Dd	distance to space vertically before a "display"
.\" These are what n/troff use for inter-paragraph distance
.\"-------
.if t .nr Dd .4v
.if n .nr Dd 1v
.\"-------
.\" Ds	begin a display, indented .5 inches from the surrounding text.
.\"
.\" Note that uses of Ds and De may NOT be nested.
.\"-------
.de Ds
.\" .RS \\$1
.sp \\n(Ddu
.in +0.5i
.nf
..
.\"-------
.\" De	end a display (no trailing vertical spacing)
.\"-------
.de De
.fi
.in
.\" .RE
..
.\"-------
.\" I stole the Xf macro from the -man macros on my machine (originally
.\" "}S", I renamed it so that it won't conflict).
.\"-------
.\" Set Cf to the name of the constant width font.
.\" It will be "C" or "(CW", typically.
.\" NOTEZ BIEN the lines defining Cf must have no trailing white space:
.\"-------
.if t .ds Cf C
.if n .ds Cf R
.\"-------
.\" Rc - Alternate Roman and Courier
.\"-------
.de Rc
.Xf R \\*(Cf \& "\\$1" "\\$2" "\\$3" "\\$4" "\\$5" "\\$6"
..
.\"-------
.\" Ic - Alternate Italic and Courier
.\"-------
.de Ic
.Xf I \\*(Cf \& "\\$1" "\\$2" "\\$3" "\\$4" "\\$5" "\\$6"
..
.\"-------
.\" Bc - Alternate Bold and Courier
.\"-------
.de Bc
.Xf B \\*(Cf \& "\\$1" "\\$2" "\\$3" "\\$4" "\\$5" "\\$6"
..
.\"-------
.\" Cr - Alternate Courier and Roman
.\"-------
.de Cr
.Xf \\*(Cf R \& "\\$1" "\\$2" "\\$3" "\\$4" "\\$5" "\\$6"
..
.\"-------
.\" Ci - Alternate Courier and Italic
.\"-------
.de Ci
.Xf \\*(Cf I \& "\\$1" "\\$2" "\\$3" "\\$4" "\\$5" "\\$6"
..
.\"-------
.\" Cb - Alternate Courier and Bold
.\"-------
.de Cb
.Xf \\*(Cf B \& "\\$1" "\\$2" "\\$3" "\\$4" "\\$5" "\\$6"
..
.\"-------
.\" Xf - Alternate fonts
.\"
.\" \$1 - first font
.\" \$2 - second font
.\" \$3 - desired word with embedded font changes, built up by recursion
.\" \$4 - text for first font
.\" \$5 - \$9 - remaining args
.\"
.\" Every time we are called:
.\"
.\" If		there is something in \$4
.\" then	Call ourself with the fonts switched,
.\"		with a new word made of the current word (\$3) and \$4
.\"		rendered in the first font,
.\"		and with the remaining args following \$4.
.\" else	We are done recursing. \$3 holds the desired output
.\"		word. We emit \$3, change to Roman font, and restore
.\"		the point size to the default.
.\" fi
.\"
.\" Use Xi to add a little bit of space after italic text.
.\"-------
.de Xf
.ds Xi
.\"-------
.\" I used to test for the italic font both by its font position
.\" and its name. Now just test by its name.
.\"
.\" .if "\\$1"2" .if !"\\$5"" .ds Xi \^
.\"-------
.if "\\$1"I" .if !"\\$5"" .ds Xi \^
.\"-------
.\" This is my original code to deal with the recursion.
.\" Evidently some nroffs can't deal with it.
.\"-------
.\" .ie !"\\$4"" \{\
.\" .	Xf \\$2 \\$1 "\\$3\\f\\$1\\$4\\*(Xi" "\\$5" "\\$6" "\\$7" "\\$8" "\\$9"
.\" .\}
.\" .el \{\\$3
.\" .	ft R	\" Restore the default font, since we don't know
.\" .		\" what the last font change was.
.\" .	ps 10	\" Restore the default point size, since it might
.\" .		\" have been changed by an argument to this macro.
.\" .\}
.\"-------
.\" Here is more portable (though less pretty) code to deal with
.\" the recursion.
.\"-------
.if !"\\$4"" .Xf \\$2 \\$1 "\\$3\\f\\$1\\$4\\*(Xi" "\\$5" "\\$6" "\\$7" "\\$8" "\\$9"
.if "\\$4"" \\$3\fR\s(10
..
.TH RC 1 "2015-05-13"
.SH NAME
rc \- shell
.SH SYNOPSIS
.B rc
.RB [ \-deiIlnopsvx ]
.RB [ \-c
.IR command ]
.RI [ arguments ]
.SH DESCRIPTION
.I rc
is a command interpreter and programming language similar to
.IR 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.
.SH OPTIONS
.TP
.Cr \-c
If
.Cr \-c
is present, commands are executed from the immediately following
argument.
Any further arguments to
.I rc
are placed in
.Cr $* .
Thus:
.Ds
.Cr "rc -c 'echo $*' 1 2 3"
.De
.TP
\&
prints out
.Ds
.Cr "1 2 3"
.De
.TP
.Cr \-d
This flag causes
.I rc
not to ignore
.Cr SIGQUIT
or
.Cr SIGTERM .
Thus
.I rc
can be made to dump core if sent
.Cr SIGQUIT .
This flag is only useful for debugging
.IR rc .
.TP
.Cr \-e
If the
.Cr \-e
flag is present, then
.I rc
will exit if any command fails (exits with non-zero status). However
.I "rc -e"
does not exit if a conditional fails. A conditional is the test of an
.Cr "if ()"
command, the test of a
.Cr "while ()"
command, or the left hand side of the
.Cr ||
or the
.Cr &&
operator.
.TP
.Cr \-i
If the
.Cr \-i
flag is present or if the input to
.I rc
is from a terminal (as determined by
.IR isatty (3))
then
.I rc
will be in
.I interactive
mode.
That is, a prompt (from
.Cr $prompt(1)\^ )
will be printed before an input line is taken, and
.I rc
will ignore
.Cr SIGINT .
.TP
.Cr \-I
If the
.Cr \-I
flag is present, or if the input to
.I rc
is not from a terminal, then
.I rc
will not be in interactive mode.
No prompts will be printed, and
.Cr SIGINT
will cause
.I rc
to exit.
.TP
.Cr \-l
If the
.Cr \-l
flag is present, or if
.IR rc 's
.Cr argv[0][0]
is a dash
.Rc ( \- ),
then
.I rc
will behave as a login shell.
That is, it will run commands from
.Cr $home/.rcrc ,
if this file exists, before reading any other input.
.TP
.Cr \-n
This flag causes
.I 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
.Cr \-x
flag,
.I rc
will print each command as it is parsed in a form similar to the one
used for exporting functions into the environment.
.TP
.Cr \-o
This flag prevents the usual practice of trying to open
.Cr /dev/null
on file descriptors 0, 1, and 2, if any of those descriptors
are inherited closed.
.TP
.Cr \-p
This flag prevents
.I rc
from initializing shell functions from the environment.
This allows
.I rc
to run in a protected mode, whereby it becomes more difficult for
an
.I rc
script to be subverted by placing false commands in the environment.
(Note that the presence of this flag does
.I not
mean that it is safe to run setuid
.I rc
scripts; the usual caveats about the setuid bit still apply.)
.TP
.Cr \-s
This flag causes
.I rc
to read from standard input.
Any arguments are placed in
.Cr $* .
.TP
.Cr \-v
This flag causes
.I rc
to echo its input
to standard error as it is read.
.TP
.Cr \-x
This flag causes
.I rc
to print every command on standard error before it is executed.
It can be useful for debugging
.I rc
scripts.
.PP
.SH COMMANDS
A simple command is a sequence of words, separated by white space
(space and tab) characters that ends with a newline, semicolon
.Rc ( ; ),
or ampersand
.Rc ( & ).
The first word of a command is the name of that command.
If the name begins with
.Cr / ,
.Cr ./ ,
or
.Cr ../ ,
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
.Cr $path .
.SS "Background Tasks"
A command ending with
.Cr &
is run in the background; that is,
the shell returns immediately rather than waiting for the command to
complete.
Background commands have
.Cr /dev/null
connected to their standard input unless an explicit redirection for
standard input is used.
.SS "Subshells"
A command prefixed with an at-sign
.Rc ( @ )
is executed in a subshell.
This insulates the parent shell from the effects
of state changing operations such as a
.B cd
or a variable assignment.
For example:
.Ds
.Cr "@ {cd ..; make}"
.De
.PP
will run
.IR make (1)
in the parent directory
.Rc ( .. ),
but leaves the shell running in the current directory.
.SS "Line continuation"
A long logical line may be continued over several physical lines by
terminating each line (except the last) with a backslash
.Rc ( \e ).
The backslash-newline sequence is treated as a space.
A backslash is not otherwise special to
.IR rc .
(In addition,
inside quotes a backslash loses its special meaning
even when it is followed by a newline.)
.SS Quoting
.IR rc
interprets several characters specially; special characters
automatically terminate words.
The following characters are special:
.Ds
.Cr "# ; & | ^ $ \` ' { } ( ) < >"
.De
.PP
The single quote
.Rc ( ' )
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
.Cr '''' .
The empty string is represented by
.Cr '' .
Thus:
.Ds
.Cr "echo 'What''s the plan, Stan?'"
.De
.PP
prints out
.Ds
.Cr "What's the plan, Stan?"
.De
.PP
The number sign
.Rc ( # )
begins a comment in
.IR 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.
.SS Grouping
Zero or more commands may be grouped within braces
.Rc (`` { ''
and
.Rc `` } ''),
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:
.Ds
.Cr "for (i) {"
.Cr "    command"
.Cr "} | command"
.De
.PP
Since pipe binds tighter than
.Cr for ,
this command does not perform what the user expects it to.
Instead, enclose the whole
.Cr for
statement in braces:
.Ds
.Cr "{for (i) command} | command"
.De
.PP
Fortunately,
.IR rc 's
grammar is simple enough that a (confident) user can
understand it by examining the skeletal
.IR yacc (1)
grammar
at the end of this man page (see the section entitled
.BR GRAMMAR ).
.SS "Input and output"
.PP
The standard output may be redirected to a file with
.Ds
.Cr "command > file"
.De
.PP
and the standard input may be taken from a file with
.Ds
.Cr "command < file"
.De
.PP
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.
.Ds
.Cr "echo 1 2 3 > foo"
.Cr "> foo echo 1 2 3"
.Cr "echo 1 2 > foo 3"
.De
.PP
File descriptors other than 0 and 1 may be specified also.
For example, to redirect standard error to a file, use:
.Ds
.Cr "command >[2] file"
.De
.PP
In order to duplicate a file descriptor, use
.Ci >[ n = m ]\fR.
Thus to redirect both standard output and standard error
to the same file, use
.Ds
.Cr "command > file >[2=1]"
.De
.PP
As in
.IR sh ,
redirections are processed from left to right.
Thus this sequence
.Ds
.Cr "command >[2=1] > file"
.De
.PP
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.
.PP
To close a file descriptor that may be open, use
.Ci >[ n =]\fR.
For example, to
close file descriptor 7:
.Ds
.Cr "command >[7=]"
.De
.PP
Note that no spaces may appear in these constructs:
.Ds
.Cr "command > [2] file"
.De
.PP
would send the output of the command to a file named
.Cr [2] ,
with the intended filename appearing in the command's argument list.
.PP
In order to place the output of a command at the end of an already
existing file, use:
.Ds
.Cr "command >> file"
.De
.PP
If the file does not exist, then it is created.
.PP
``Here documents'' are supported as in
.I sh
with the use of
.Ds
.Cr "command << 'eof-marker'"
.De
.PP
Subsequent lines form the standard input of
the command, till a line containing just the
marker, in this case
.Cr eof-marker ,
is encountered.
.PP
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
.BR "Flat Lists" ,
below),
and if a
.Cr ^
character follows a variable name, it is deleted.
This allows the unambiguous use of variables adjacent to text, as in
.Ds
.Cr $variable^follow
.De
.PP
To include a literal
.Cr $
in a here document when an unquoted end-of-file marker is being used,
enter it as
.Cr $$ .
.PP
Additionally,
.I 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:
.Ds
.Cr "cat <<< 'this is a here string' | wc"
.De
.PP
(This feature enables
.I rc
to export functions using here documents into the environment;
the author does not expect users to find this feature useful.)
.SS Pipes
Two or more commands may be combined in a pipeline by placing the
vertical bar
.Rc ( \||\| )
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
.Ci |[ n = m ]
indicates that file descriptor
.I n
of the left process is connected to
file descriptor
.I m
of the right process.
.Ci |[ n ]
is a shorthand for
.Ci |[ n =0]\fR.
As an example, to pipe the standard error of a command to
.IR wc (1),
use:
.Ds
.Cr "command |[2] wc"
.De
.PP
As with file redirections, no spaces may occur in the construct specifying
numbered file descriptors.
.PP
The exit status of a pipeline is considered true if and only if every
command in the pipeline exits true.
.SS "Commands as Arguments"
Some commands, like
.IR cmp (1)
or
.IR 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
.I cmp
can read the output of two other commands at once.
.I rc
does it like this:
.Ds
.Cr "cmp <{command} <{command}"
.De
.PP
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
.IR lseek (2)
on a pipe, commands that use
.IR lseek (2)
will hang.
For example, some versions of
.IR diff (1)
use
.IR lseek (2)
on their inputs.
.PP
Data can be sent down a pipe to several commands using
.IR tee (1)
and the output version of this notation:
.Ds
.Cr "echo hi there | tee >{sed 's/^/p1 /'} >{sed 's/^/p2 /'}"
.De
.SH "CONTROL STRUCTURES"
The following may be used for control flow in
.IR rc :
.SS "If-Else Statements"
.PD 0
.sp
.Ci "if (" test ") {"
.br
.I "    cmd"
.br
.TP
.Ci "} else " cmd
The
.I 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
.Cr else
statement is valid only if it
follows a close-brace on the same line.
Otherwise, the
.Cr if
is taken to be a simple-if:
.Ds
.Cr "if (test)"
.Cr "    command"
.De
.PD
.SS "While and For Loops"
.TP
.Ci "while (" test ) " cmd"
.I rc
executes the
.I test
and performs the command as long as the
.I test
is true.
.TP
.Ci "for (" var " in " list ) " cmd"
.I rc
sets
.I var
to each element of
.I list
(which may contain variables and backquote substitutions) and runs
.IR cmd .
If
.Rc `` in
.IR list ''
is omitted, then
.I rc
will set
.I var
to each element of
.Cr $* .
For example:
.Ds
.Cr "for (i in \`{ls -F | grep '\e*$' | sed 's/\e*$//'}) { commands }"
.De
.TP
\&
will set
.Cr $i
to the name of each file in the current directory that is
executable.
.SS "Switch"
.TP
.Ci "switch (" list ") { case" " ..." " }"
.I rc
looks inside the braces after a
.Cr switch
for statements beginning with the word
.Cr case .
If any of the patterns following
.Cr case
match the list supplied to
.Cr switch ,
then the commands up until the next
.Cr case
statement are executed.
The metacharacters
.Cr "*" ,
.Cr [
or
.Cr ?
should not be quoted;
matching is performed only against the strings in
.IR list ,
not against file names.
(Matching for case statements is the same as for the
.Cr ~
command.)
.SS "Logical Operators"
There are a number of operators in
.I rc
which depend on the exit status of a command.
.Ds
.Cr "command && command"
.De
.PP
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).
.Ds
.Cr "command || command"
.De
.PP
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).
.Ds
.Cr "! command"
.De
.PP
negates the exit status of a command.
.SH "PATTERN MATCHING"
There are two forms of pattern matching in
.IR rc .
One is traditional shell globbing.
This occurs in matching for file names in argument lists:
.Ds
.Cr "command argument argument ..."
.De
.PP
When the characters
.Cr "*" ,
.Cr [
or
.Cr ?
occur in an argument or command,
.I rc
looks at the
argument as a pattern for matching against files.
(Contrary to the behavior other shells exhibit,
.I rc
will only perform pattern matching if a metacharacter occurs unquoted and
literally in the input.
Thus,
.Ds
.Cr "foo='*'"
.Cr "echo $foo"
.De
.PP
will always echo just a star.
In order for non-literal metacharacters to be expanded, an
.Cr eval
statement must be used in order to rescan the input.)
Pattern matching occurs according to the following rules: a
.Cr *
matches any number (including zero) of
characters.
A
.Cr ?
matches any single character, and a
.Cr [
followed by a
number of characters followed by a
.Cr ]
matches a single character in that
class.
The rules for character class matching are the same as those for
.IR ed (1),
with the exception that character class negation is achieved
with the tilde
.Rc ( ~ ),
not the caret
.Rc ( ^ ),
since the caret already means
something else in
.IR rc .
.PP
.I rc
also matches patterns against strings with the
.Cr ~
command:
.Ds
.Cr "~ subject pattern pattern ..."
.De
.PP
The
.Cr ~
command succeeds (sets
.Cr $status
to zero) if and only if one of the
.Cr pattern s
matches
.Cr subject .
Thus
.Ds
.Cr "~ foo f*"
.De
.PP
succeeds (sets status to zero), while
.Ds
.Cr "~ bar f*"
.De
.PP
fails (sets status to one).
.PP
The null list is matched by the null list, so
.Ds
.Cr "~ $foo ()"
.De
.PP
checks to see whether
.Cr $foo
is empty or not. Because
.I rc
does not have hierarchical lists, the test for emptiness cannot be
combined with other tests. To test whether
.Cr $foo
is empty, or one of the strings
.Cr nada
or
.Cr rien ,
do
.I not
write
.Ds
.Cr "~ $x () nada rien # WRONG means the same as: ~ $x nada rien"
.De
.PP
instead write
.Ds
.Cr "~ $x () || ~ $x nada rien"
.De
.PP
Another way to test if
.Cr $foo
is empty is
.Ds
.Cr "~ $#foo 0"
.De
.PP
Note that inside a
.Cr ~
command
.I rc
does not match patterns against file
names, so it is not necessary to quote the characters
.Cr "*" ,
.Cr [
and
.Cr "?" .
However,
.I rc
does expand the subject against filenames if it contains
metacharacters.
Thus, the command
.Ds
.Cr "~ * ?"
.De
.PP
succeeds if any of the files in the current directory have a
single-character name.
.PP
If the
.Cr ~
command is given a list as its first
argument, then a successful match against any of the elements of that
list will cause
.Cr ~
to succeed.
For example:
.Ds
.Cr "~ (foo goo zoo) z*"
.De
.PP
is true.
.SH "LISTS AND VARIABLES"
The primary data structure in
.IR rc
is the list, which is a sequence of words.
Parentheses are used to group lists.
The empty list is represented by
.Cr "()" .
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
.Ds
.Cr "one two three"

.Cr "(one two three)"

.Cr "((one) () ((two three)))"
.De
.PP
Note that the null string,
.Cr "''" ,
and the null list,
.Cr "()" ,
are two very different things.
Assigning the null string to a variable is a valid operation, but it
does not remove its definition.
.Ds
.Cr "null = '' empty = () echo $#null $#empty"
.De
.PP
produces the output
.Ds
.Cr "1 0"
.De
.SS "List Concatenation"
Two lists may be joined by the concatenation operator
.Rc ( ^ ).
Concatenation works according to the following rules:
if the two lists have the same number of elements,
then concatenation is pairwise:
.Ds
.Cr "echo (a\- b\- c\-)^(1 2 3)"
.De
.PP
produces the output
.Ds
.Cr "a\-1 b\-2 c\-3"
.De
.PP
Otherwise, at least one of the lists must have a single element,
and then the concatenation is distributive:
.Ds
.Cr "cc \-^(O g c) (malloc alloca)^.c"
.De
.PP
has the effect of performing the command
.Ds
.Cr "cc \-O \-g \-c malloc.c alloca.c"
.De
.PP
A single word is a list of length one, so
.Ds
.Cr "echo foo^bar"
.De
.PP
produces the output
.Ds
.Cr foobar
.De
.SS "Free Carets"
.I rc
inserts carets (concatenation operators) for free in certain situations,
in order to save some typing on the user's behalf.
For
example, the above example could also be typed in as:
.Ds
.Cr "opts=(O g c) files=(malloc alloca) cc \-$opts $files.c"
.De
.PP
.I rc
takes care to insert a free caret between the
.Rc `` \- ''
and
.Cr "$opts" ,
as well
as between
.Cr $files
and
.Cr ".c" .
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
.I rc
inserts a caret between them.
.SS "Variables"
A list may be assigned to a variable, using the notation:
.Ds
.Ic var " = " list
.De
.PP
The special variable
.Cr *
may also be assigned to using this notation;
.I rc
has no
.B set
builtin.
.PP
Any non-empty sequence of characters, except a sequence including only
digits, may be used as a variable name.
Any character except
.Cr =
may be used, but special characters must be quoted.
All user-defined variables are exported into the environment.
.PP
The value of a variable is referenced with the dollar
.Rc ( $ )
operator:
.Ds
.Ci $ var
.De
.PP
Any variable which has not been assigned a value returns the null list,
.Cr "()" ,
when referenced.
Multiple references are allowed:
.Ds
.Cr "a = foo"
.Cr "b = a"
.Cr "echo $ $ b"
.De
.PP
prints
.Ds
.Cr foo
.De
.PP
A variable's definition may also be removed by
assigning the null list to a variable:
.Ds
.Ic var =()
.De
.PP
For ``free careting'' to work correctly,
.I rc
must make certain assumptions
about what characters may appear in a variable name.
.I rc
assumes that a variable name consists only of alphanumeric characters,
underscore
.Rc ( \|_\| )
and star
.Rc ( * ).
To reference a variable with other
characters in its name, quote the variable name.
Thus:
.Ds
.Cr "echo $'we$Ird:Variab!le'"
.De
.SS "Local Variables"
Any number of variable assignments may be made local to a single
command by typing:
.Ds
.Cr "a=foo b=bar ... command"
.De
.PP
The command may be a compound command, so for example:
.Ds
.Cr "path=. ifs=() {"
.Cr "    " ...
.Cr }
.De
.PP
sets
.Cr path
to
.Cr .
and removes
.Cr ifs
for the duration of one long compound command.
.SS "Variable Subscripts"
Variables may be subscripted with the notation
.Ds
.Ci $var( n )
.De
.PP
where
.I 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,
.Ds
.Cr "a=(one two three)"
.Cr "echo $a(3 3 3)"
.De
.PP
prints
.Ds
.Cr "three three three"
.De
.PP
If
.I n
references a nonexistent element, then
.Ci $var( n )
returns the null list.
The notation
.Ci "$" n\fR,
where
.I n
is an integer, is a shorthand for
.Ci $*( n )\fR.
Thus,
.IR rc 's
arguments may be referred to as
.Cr "$1" ,
.Cr "$2" ,
and so on.
.PP
Note also that the list of subscripts may be given by any of
.IR rc 's
list operations:
.Ds
.Cr "$var(\`{awk 'BEGIN{for(i=1;i<=10;i++)print i;exit; }'})"
.De
.PP
returns the first 10 elements of
.Cr $var .
.PP
To count the number of elements in a variable, use
.Ds
.Cr $#var
.De
.PP
This returns a single-element list, with the number of elements in
.Cr $var .
.SS "Flat Lists"
In order to create a single-element list from a multi-element list,
with the components space-separated, use the dollar-caret
.Rc ( $^ )
operator:
.Ds
.Cr $^var
.De
.PP
This is useful when the normal list concatenation rules need to be
bypassed.
For example, to append a single period at the end of
.Cr $path ,
use:
.Ds
.Cr "echo $^path."
.De
.PP
For compatibility with the Plan 9 rc,
.Ds
.Cr $"var
.De
.PP
is accepted as a synonym for dollar-caret.
.SS "Backquote Substitution"
A list may be formed from the output of a command by using backquote
substitution:
.Ds
.Cr "\`{ command }"
.De
.PP
returns a list formed from the standard output of the command in braces.
.Cr $ifs
is used to split the output into list elements.
By default,
.Cr $ifs
has the value space-tab-newline.
.PP
The braces may be omitted if the command is a single word.
Thus
.Cr \`ls
may be used instead of
.Cr "\`{ls}" .
This last feature can be used to create shortcuts by defining functions that
expand to useful argument lists.
For example:
.Ds
.Cr "fn src { echo *.[chy] }"
.De
.PP
followed by
.Ds
.Cr "wc \`src"
.De
.PP
This will print out a word-count of all C source files in the current
directory.
.PP
In order to override the value of
.Cr $ifs
for a single backquote
substitution, use:
.Ds
.Cr "\`\` (ifs-list) { command }"
.De
.PP
.Cr $ifs
will be temporarily ignored and the command's output will be split as specified by
the list following the double backquote.
For example:
.Ds
.Cr "\`\` ($nl :) {cat /etc/passwd}"
.De
.PP
splits up
.Cr /etc/passwd
into fields.
.PP
As a convenience,
.I rc
defines
.Cr $nl
to contain the newline character, and
.Cr $tab
to contain the tab character. Thus, if you want to process everything in the
current directory, but in a random order, you could use:
.Ds
.Cr "for (f in \`\` $nl {ls | shuf}) { ... process $f }"
.De
.PP
This will correctly handle filenames that contain spaces.
.PP
Note that
.I rc
scripts that use backquote substitution should avoid relying on the default
values of
.Cr $ifs ,
.Cr $nl ,
or
.Cr $tab .
Instead, they should explicitly set what they need.
.SH "SPECIAL VARIABLES"
Several variables are known to
.I rc
and are treated specially.
In the following list, ``default'' indicates that
.I 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.
.PP
Also, ``alias'' means that the variable is aliased to the same name in
capitals.
For example, an assignment to
.Cr $cdpath
causes an automatic assignment to
.Cr $CDPATH ,
and vice-versa.
If
.Cr $CDPATH
is set when
.I rc
is started, its value is imported into
.Cr $cdpath .
.Cr $cdpath
and
.Cr $path
are
.I rc
lists;
.Cr $CDPATH
and
.Cr $PATH
are colon-separated lists.
Only the names spelt in capitals are exported into the environment.
.TP
.Cr * " (no-export)"
The argument list of
.IR rc .
.Cr "$1, $2,"
etc. are the same as
.Cr $*(1) ,
.Cr $*(2) ,
etc.
.TP
.Cr 0 " (default no-export)"
The variable
.Cr $0
holds the value of
.Cr argv[0]
with which
.I rc
was invoked.
Additionally,
.Cr $0
is set to the name of a function for the duration of
the execution of that function, and
.Cr $0
is also set to the name of the
file being interpreted for the duration of a
.Cr .
command.
.Cr $0
is not an element of
.Cr $* ,
and is never treated as one.
.TP
.Cr apid " (no-export)"
The process ID of the last process started in the background.
.TP
.Cr apids " (no-export read-only)"
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.
.TP
.Cr bqstatus " (no-export)"
The exit status of the
.I rc
forked to execute the most recent backquote substitution. Note that, unlike
.Cr $status ,
.Cr $bqstatus
is always a single element list (see
.BR "EXIT STATUS"
below). For example:
.Ds
.Cr "echo foo |grep bar; whatis status"
.De
.TP
\&
prints
.Ds
.Cr "status=(0 1)"
.De
.TP
\&
whereas
.Ds
.Cr "x=`{echo foo |grep bar}; whatis bqstatus"
.De
.TP
\&
prints
.Ds
.Cr "bqstatus=1"
.De
.TP
.Cr cdpath " (alias)"
A list of directories to search for the target of a
.B cd
command.
The empty string stands for the current directory.
Note that if the
.Cr $cdpath
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.
.TP
.Cr history
.Cr $history
contains the name of a file to which commands are appended as
.I rc
reads them.
This facilitates the use of a stand-alone history program
(such as
.IR history (1))
which parses the contents of the history file and presents them to
.I rc
for reinterpretation.
If
.Cr $history
is not set, then
.I rc
does not append commands to any file.
.TP
.Cr home " (alias)"
The default directory for the builtin
.B cd
command, and the directory in which
.I rc
looks to find its initialization file,
.Cr .rcrc ,
if
.I rc
has been started up as a login shell.
.TP
.Cr ifs " (default)"
The internal field separator, used for splitting up the output of
backquote commands for digestion as a list. On startup,
.I rc
assigns the list containing the characters space, tab, and newline to
.Cr $ifs .
.TP
.Cr nl " (default)"
Contains the newline character (see
.BR "Backquote substitution"
above).
.TP
.Cr path " (alias)"
This is a list of directories to search in for commands.
The empty string stands for the current directory.
If neither
.Cr $PATH
nor
.Cr $path
is set at startup time,
.Cr $path
assumes a default value suitable for your system.
This is typically
.Cr "(/usr/local/bin /usr/bin /usr/ucb /bin .)"
.TP
.Cr pid " (default no-export)"
On startup,
.Cr $pid
is initialized to the numeric process ID of the currently running
.IR rc .
.TP
.Cr prompt " (default)"
This variable holds the two prompts (in list form, of course) that
.I rc
prints.
.Cr $prompt(1)
is printed before each command is read, and
.Cr $prompt(2)
is printed when input is expected to continue on the next
line.
.I rc
sets
.Cr $prompt
to
.Cr "('; ' '')"
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 $prompt(2) 's
on the screen,
and can therefore be grabbed by a mouse and placed
directly into a file for use as a shell script, without further editing
being necessary.
.TP
.Cr prompt " (function)"
If this function is defined, then it gets executed every time
.I rc
is about to print
.Cr "$prompt(1)" .
.TP
.Cr status " (no-export read-only)"
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
.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)" .
.TP
.Cr tab " (default)"
Contains the tab character (see
.BR "Backquote substitution"
above).
.TP
.Cr version " (default)"
On startup, the first element of this list variable is initialized to
a string which identifies this version of
.IR rc .
The second element is initialized to a string which can be found by
.IR ident (1)
and the
.I what
command of 
.IR sccs (1).
.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 $* }"
.De
.PP
but not
.Ds
.Cr "fn l { ls -FC } # WRONG"
.De
.SH "INTERRUPTS AND SIGNALS"
.I rc
recognizes a number of signals, and allows the user to define shell
functions which act as signal handlers.
.I rc
by default traps
.Cr SIGINT
when it is in interactive mode.
.Cr SIGQUIT
and
.Cr SIGTERM
are ignored, unless
.I rc
has been invoked with the
.Cr \-d
flag.
However, user-defined signal handlers may be written for these and
all other signals.
The way to define a signal handler is to
write a function by the name of the signal in lower case.
Thus:
.Ds
.Cr "fn sighup { echo hangup; rm /tmp/rc$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
.Cr 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.
For example:
.Ds
.Cr "fn ls { builtin ls -FC $* }"
.De
.TP
\&
is a reasonable way to pass a default set of arguments to
.Cr ls (1),
whereas
.Ds
.Cr "fn ls { ls -FC $* } # WRONG"
.De
.TP
\&
is a non-terminating recursion, which will cause
.Cr rc
to exhaust its stack space and (eventually) terminate if it is executed.
.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
.B continue
Continues the innermost
.Cr for
or
.Cr while
loop,
as in C.
It is an error to invoke
.B continue
outside of a loop.
.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
\fBflag\fR \fIf\fR [ \fB+\fR | \fB\-\fR ]
Test, set (\fB+\fR), or reset (\fB\-\fR) command-line flag
.IR f .
For example, a script that requires ``exit if command fails'' semantics can say
.Ds
.Cr "flag e +"
.De
.TP
\&
Some flags cannot be set or reset using
.BR flag ,
but they can still be tested. These are
.BR c ,
.BR d ,
.BR l ,
.BR o ,
.BR p ,
and
.BR s .
As a special case,
.Cr "flag i"
operates on
.BR rc 's
internal
.IR interactive
flag, which may have been set by
.Cr -i
on the command line, or if standard input was a terminal; there is no
.Cr "flag I" .
.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 resource 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 ,
.BR coredumpsize ,
.BR memoryuse ,
and, where supported,
.BR descriptors ,
.BR memoryuse ,
.BR memoryrss ,
.BR maxproc ,
.BR memorylocked ,
and
.BR filelocks .
For example:
.Ds
.Cr "limit coredumpsize 0"
.De
.TP
\&
disables core dumps.
To set a soft limit equal to the hard limit:
.Ds
.Cr "limit `{limit -h datasize}"
.De
.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 valid exit status, or a list of them.
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.
.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 one or more processes with the specified
.IR pid s,
which must have been started by
.IR rc ,
to exit. The status of each specified process is appended to
.Cr " $status" .
If no
.I pid
is specified,
.I rc
waits for all its child processes to exit, and returns the
status of the last one.
.TP
\fBwhatis \fR[\fB\-b\fR] \fR[\fB\-f\fR] \fR[\fB\-p\fR] \fR[\fB\-s\fR] \fR[\fB\-v\fR] [\fB\-\|\-\fR] [\fIname ...\fR]
Prints a definition of the named objects.
For builtins,
.Cr builtin
.I foo
is printed; for functions, including signal handlers, their definitions
are printed; for executable files, path names are printed; and for
variables, their values are printed.
The flags restrict output to builtins, functions, executable
programs, signal handlers, and variables, respectively.
If no
.IR name s
are specified,
.I rc
lists all objects of that type.
(This is not permitted for
.Cr \-p .)
Without arguments,
.Cr whatis
is equivalent to
.Cr "whatis -fv" ,
and prints the values of all shell variables and functions.
.TP
\&
Note that
.B whatis
output is suitable for input to
.IR rc ;
by saving the output of
.B whatis
in a file, it should be possible to recreate the state of
.I rc
by sourcing this file with a
.Cr .
command.
Another note:
.Cr "whatis -s > file"
cannot be used to store the state of
.IR rc 's
signal handlers in a file, because builtins with redirections
are run in a subshell, and
.I rc
always restores signal handlers to their default value after a
.Cr fork() .
.TP
\&
Since
.B whatis
uses
.IR getopt (3)
to parse its arguments, you can use the special argument
.Cr "\-\|\-"
to terminate its flags.
This allows you to use names beginning with a dash, such as
the
.IR history (1)
commands.
For example,
.Ds
.Cr "whatis \-\|\- \-p"
.De
.SH EXAMPLES
The
.B shift
builtin only shifts
.Cr "$*" .
This function can shift any variable (except
.Cr "$_lshift" ).
.Ds
.Cr "fn lshift { _lshift=$* *=$$1 { shift $_lshift(2); $_lshift(1)=$* } }"
.De
.PP
With this definition in place,
.Ds
.Cr "walrus = (shoes ships sealing-wax cabbages kings)"
.Cr "lshift walrus 3"
.Cr "whatis walrus"
.De
.PP
prints
.Ds
.Cr "walrus=(cabbages kings)"
.De
.PP
The
.Cr $^var
operator flattens a list by separating each element with a space.
This function allows the separator to be an arbitrary string.
.Ds
.Cr "fn lflat {"
.Cr "  lflat=$*; *=$$1"
.Cr "  while () {"
.Cr "    echo -n $1; shift"
.Cr "    ~ $#* 0 && break"
.Cr "    echo -n $lflat(2)"
.Cr "  }"
.Cr "}"
.De
.PP
With this definition in place,
.Ds
.Cr "hops=(uunet mcvax ukc tlg)"
.Cr "lflat hops !"
.De
.PP
prints (with no final newline)
.Ds
.Cr uunet!mcvax!ukc!tlg
.De
.SH "EXIT STATUS"
The exit status of
.I rc
is normally the same as that of the last command executed.
If the
last command was a pipeline,
.I rc
exits
.Cr 0
if every command in the pipeline did; otherwise it exits
.Cr 1 .
.PP
.I rc
can be made to exit with a particular status using the
.B exit
builtin.
.SH "LINE EDITING"
.I rc
is typically built against a line editing library.
On GNU/Linux systems this will usually be the GNU
.I readline
library.
On *BSD systems it is more likely to be the BSD
.I editline
library.
Please consult the appropriate library documentation for details of how to use
and configure line editing.
.SS "Tilde Expansion"
Since
.I rc
does not support tilde expansion (converting
.Cr ~foo
to the home directory of user
.Cr foo ),
it is sometimes suggested by users as a
possible enhancement.
The authors and maintainers of
.I rc
have a proud history of resisting such feature requests.
So it is worth noting here that GNU
.I readline
can expand tildes.
Add this line to the file
.Cr .inputrc
in your home directory.
.Ds
.Cr "set expand-tilde on"
.De
.PP
and then use the key sequence
.Cr "M-~"
to perform tilde expansion on the current word.
See the
.I readline
documentation for further details.
.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 '^' '='
%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 optcaret '=' optcaret 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 */ %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 '\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 was copied from the
.I rc
that Tom Duff wrote at Bell Labs.
.SH BUGS
There is a compile-time limit on the number of
.Cr ;
separated commands in a line: usually 500.
This is sometimes a problem for automatically generated scripts:
substituting the newline character for
.Cr ;
avoids the limit.
.PP
On modern systems that support
.Cr /dev/fd
or
.Cr /proc/self/fd ,
.Cr <{foo}
style redirection is implemented that way.
However, on older systems it is implemented with named pipes.
Allegedly, 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.
(The current maintainer has never seen this, but then he
doesn't use systems which lack
.Cr /dev/fd
any more.
If anybody can reproduce this problem, please let the maintainer know.)
.PP
The
.B echo
command does not need to be a builtin. It is one for reasons of
performance and portability (of
.I rc
scripts).
.PP
There should be a way to avoid exporting a variable.
.PP
Extra parentheses around a
.Cr ~
expression or a
.Cr !
expression are a syntax error.
Thus, this code is illegal.
.Ds
.Cr "while ((~ $1 -*) && (! ~ $1 --)) { ..."
.De
.TP
The redundant inner parentheses must be omitted.
.PP
Variable subscripting cannot be used in here documents.
.PP
The
.Cr limit
builtin silently ignores extra arguments.
.PP
Backquote substitution never produces empty strings - multiple
consecutive occurrences of the separator are treated the same as a
single occurrence.
.Ds
.Cr "ifs=! { x = `{echo -n a!!b}; whatis x }"
.Cr "x=(a b) # NOT x=(a '' b)"
.PP
Bug reports should be mailed to
.Cr "<toby@paccrat.org>" .
.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 Tenth Edition
.I rc
does not have the
.B else
keyword.
Instead,
.B if
is optionally followed by
an
.B "if not"
clause which is executed
if the preceding
.B if
test does not succeed.
.PP
Backquotes are slightly different in Tenth Edition
.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
For
.Cr .
.IR file ,
the Tenth Edition
.IR rc
searches
.Cr $path
for
.IR file .
This
.I rc
does not, since it is not considered useful.
.PP
The list flattening operator,
.Cr $^foo ,
is spelt
.Cr "$""foo"
in those versions of the Bell Labs
.IR rc
which have it.
.PP
The following are all new with this version of
.IR rc :
The
.Cr \-n
flag,
here strings (they facilitate exporting of functions
with here documents into the environment),
the
.B return,
.B continue,
and
.B break
keywords,
the
.B echo
builtin,
the
.Cr bqstatus
and
.Cr version
variables,
the
.Cr prompt
function,
support for GNU
.IR readline
and other line editing libraries.
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,
Tenth Edition,
Volume 2. (Saunders College Publishing)
.PP
.Cr https://doc.cat-v.org/plan_9/2nd_edition/papers/rc/ ,
an updated version of the above paper.
.PP
.IR history (1)