rc.1

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.\" 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
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.\" in true nroffs must be written
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.\" .Cr "exec >[2] err.out"
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.\" 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 ([e-mail])
.\" for pointing out these problems.
.\"
.\" Note that sentences should end at the end of a line.  nroff and
.\" troff will supply the correct intersentence spacing, but only if
.\" the sentences end at the end of a line.  Explicit spaces, if given,
.\" are apparently honored and the normal intersentence spacing is
.\" supressed.
.\"
.\" DaviD W. Sanderson
.\"-------
.\" Dd	distance to space vertically before a "display"
.\" These are what n/troff use for interparagraph distance
.\"-------
.if t .nr Dd .4v
.if n .nr Dd 1v
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.\" 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
..
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.\" 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"
..
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.\" Ic - Alternate Italic and Courier
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.de Ic
.Xf I \\*(Cf \& "\\$1" "\\$2" "\\$3" "\\$4" "\\$5" "\\$6"
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.\" Bc - Alternate Bold and Courier
.\"-------
.de Bc
.Xf B \\*(Cf \& "\\$1" "\\$2" "\\$3" "\\$4" "\\$5" "\\$6"
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.\" Cr - Alternate Courier and Roman
.\"-------
.de Cr
.Xf \\*(Cf R \& "\\$1" "\\$2" "\\$3" "\\$4" "\\$5" "\\$6"
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.\" Ci - Alternate Courier and Italic
.\"-------
.de Ci
.Xf \\*(Cf I \& "\\$1" "\\$2" "\\$3" "\\$4" "\\$5" "\\$6"
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.\" 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\s10
..
.TH RC 1 "28 April 1991"
.SH NAME
rc \- shell
.SH SYNOPSIS
.B rc
.RB [ \-eixvldnpo ]
.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 \-e
If the
.Cr \-e
option is present, then
.I rc
will exit if the exit status of a command is false (nonzero).
.I rc
will not exit, however, if a conditional fails, e.g., an
.Cr if()
command.
.TP
.Cr \-i
If the
.Cr \-i
option 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 the signals
.Cr SIGINT
and
.Cr SIGQUIT .
.TP
.Cr \-x
This option will make
.I rc
print every command on standard error before it is executed.
It can be useful for debugging
.I rc
scripts.
.TP
.Cr \-v
This option will echo input to
.I rc
on standard error as it is read.
.TP
.Cr \-l
If the
.Cr \-l
option 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 try to run commands present in
.Cr $home/.rcrc ,
if this file exists, before reading any other input.
.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 option is only useful for debugging
.IR rc .
.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
option,
.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 \-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 this presence of this option does NOT mean that it is safe to
run setuid
.I rc
scripts; the usual caveats about the setuid bit still apply.)
.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 \-c
If
.Cr \-c
is present, commands are executed from the immediately following
argument.
Any further arguments to
.I rc
are placed in
.Cr $* .
.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 a
.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
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
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
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
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
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.
Its 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
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.
A 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,
most 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