RC(1)                       General Commands Manual                      RC(1)

       rc - shell

       rc [-deiIlnopsvx] [-c command] [arguments]

       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.

       -c     If -c is present, commands are executed from the immediately
              following argument.  Any further arguments to rc are placed in
              $*.  Thus:

                   rc -c 'echo $*' 1 2 3

              prints out

                   1 2 3

       -d     This flag causes rc not to ignore SIGQUIT or SIGTERM.  Thus rc
              can be made to dump core if sent SIGQUIT.  This flag is only
              useful for debugging rc.

       -e     If the -e flag is present, then rc will exit if the exit status
              of a command is false (nonzero).  rc will not exit, however, if
              a conditional fails, e.g., an if() command.

       -i     If the -i 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)) will be
              printed before an input line is taken, and rc will ignore

       -I     If the -I 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 SIGINT will cause rc to exit.

       -l     If the -l flag is present, or if rc's argv[0][0] is a dash (-),
              then rc will behave as a login shell.  That is, it will run
              commands from $home/.rcrc, if this file exists, before reading
              any other input.

       -n     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 -x flag, rc will print
              each command as it is parsed in a form similar to the one used
              for exporting functions into the environment.

       -o     This flag prevents the usual practice of trying to open
              /dev/null on file descriptors 0, 1, and 2, if any of those
              descriptors are inherited closed.

       -p     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

       -s     This flag causes rc to read from standard input.  Any arguments
              are placed in $*.

       -v     This flag causes rc to echo its input to standard error as it is

       -x     This flag causes rc to print every command on standard error
              before it is executed.  It can be useful for debugging rc

       A simple command is a sequence of words, separated by white space
       (space and tab) characters that ends with a newline, semicolon (;), or
       ampersand (&).  The first word of a command is the name of that
       command.  If the name begins with /, ./, or ../, 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.

   Background Tasks
       A command ending with & is run in the background; that is, the shell
       returns immediately rather than waiting for the command to complete.
       Background commands have /dev/null connected to their standard input
       unless an explicit redirection for standard input is used.

       A command prefixed with an at-sign (@) 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}

       will run make(1) in the parent directory (..), 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 (\).  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.)

       rc interprets several characters specially; special characters
       automatically terminate words.  The following characters are special:

            # ; & | ^ $ = ` ' { } ( ) < >

       The single quote (') 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 ''''.  The empty string is represented by ''.  Thus:

            echo 'What''s the plan, Stan?'

       prints out

            What's the plan, Stan?

       The number sign (#) 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.

       Zero or more commands may be grouped within braces (``{'' and ``}''),
       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) {
            } | command

       Since pipe binds tighter than for, this command does not perform what
       the user expects it to.  Instead, enclose the whole for statement in

            {for (i) command} | command

       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 > file

       and the standard input may be taken from a file with

            command < file

       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 > foo
            > foo echo 1 2 3
            echo 1 2 > foo 3

       File descriptors other than 0 and 1 may be specified also.  For
       example, to redirect standard error to a file, use:

            command >[2] file

       In order to duplicate a file descriptor, use >[n=m].  Thus to redirect
       both standard output and standard error to the same file, use

            command > file >[2=1]

       As in sh, redirections are processed from left to right.  Thus this

            command >[2=1] > file

       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=].  For example,
       to close file descriptor 7:

            command >[7=]

       Note that no spaces may appear in these constructs:

            command > [2] file

       would send the output of the command to a file named [2], 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 >> file

       If the file does not exist, then it is created.

       ``Here documents'' are supported as in sh with the use of

            command << 'eof-marker'

       Subsequent lines form the standard input of the command, till a line
       containing just the marker, in this case eof-marker, 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 ^ character follows a variable name, it is
       deleted.  This allows the unambiguous use of variables adjacent to
       text, as in


       To include a literal $ in a here document when an unquoted end-of-file
       marker is being used, enter it as $$.

       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' | wc

       (This feature enables rc to export functions using here documents into
       the environment; the author does not expect users to find this feature

       Two or more commands may be combined in a pipeline by placing the
       vertical bar (|) 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]
       indicates that file descriptor n of the left process is connected to
       file descriptor m of the right process.  |[n] is a shorthand for
       |[n=0].  As an example, to pipe the standard error of a command to
       wc(1), use:

            command |[2] wc

       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}

       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 /'}

       The following may be used for control flow in rc:

   If-Else Statements
       if (test) {
       } else cmd
              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 else statement
              is valid only if it follows a close-brace on the same line.
              Otherwise, the if is taken to be a simple-if:

                   if (test)

   While and For Loops
       while (test) cmd
              rc executes the test and performs the command as long as the
              test is true.

       for (var in list) cmd
              rc sets var to each element of list (which may contain variables
              and backquote substitutions) and runs cmd.  If ``in list'' is
              omitted, then rc will set var to each element of $*.  For

                   for (i in `{ls -F | grep '\*$' | sed 's/\*$//'}) { commands }

              will set $i to the name of each file in the current directory
              that is executable.

       switch (list) { case ... }
              rc looks inside the braces after a switch for statements
              beginning with the word case.  If any of the patterns following
              case match the list supplied to switch, then the commands up
              until the next case statement are executed.  The metacharacters
              *, [ or ?  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 ~ command.)

   Logical Operators
       There are a number of operators in rc which depend on the exit status
       of a command.

            command && command

       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

            command || command

       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).

            ! command

       negates the exit status of a command.

       There are two forms of pattern matching in rc.  One is traditional
       shell globbing.  This occurs in matching for file names in argument

            command argument argument ...

       When the characters *, [ or ?  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,

            echo $foo

       will always echo just a star.  In order for non-literal metacharacters
       to be expanded, an eval statement must be used in order to rescan the
       input.)  Pattern matching occurs according to the following rules: a *
       matches any number (including zero) of characters.  A ?  matches any
       single character, and a [ followed by a number of characters followed
       by a ] 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 (~),
       not the caret (^), since the caret already means something else in rc.

       rc also matches patterns against strings with the ~ command:

            ~ subject pattern pattern ...

       ~ sets $status to zero if and only if a supplied pattern matches any
       single element of the subject list.  Thus

            ~ foo f*

       sets status to zero, while

            ~ (bar baz) f*

       sets status to one.  The null list is matched by the null list, so

            ~ $foo ()

       checks to see whether $foo is empty or not.  This may also be achieved
       by the test

            ~ $#foo 0

       Note that inside a ~ command rc does not match patterns against file
       names, so it is not necessary to quote the characters *, [ and ?.
       However, rc does expand the subject against filenames if it contains
       metacharacters.  Thus, the command

            ~ * ?

       returns true if any of the files in the current directory have a
       single-character name.  If the ~ command is given a list as its first
       argument, then a successful match against any of the elements of that
       list will cause ~ to return true.  For example:

            ~ (foo goo zoo) z*

       is true.

       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 ().  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 three

            (one two three)

            ((one) () ((two three)))

       Note that the null string, '', and the null list, (), 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 $#empty

       produces the output

            1 0

   List Concatenation
       Two lists may be joined by the concatenation operator (^).
       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)

       produces the output

            a-1 b-2 c-3

       Otherwise, at least one of the lists must have a single element, and
       then the concatenation is distributive:

            cc -^(O g c) (malloc alloca)^.c

       has the effect of performing the command

            cc -O -g -c malloc.c alloca.c

       A single word is a list of length one, so

            echo foo^bar

       produces the output


   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.c

       rc takes care to insert a free-caret between the ``-'' and $opts, as
       well as between $files and .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 rc inserts a caret between them.

       A list may be assigned to a variable, using the notation:

            var = list

       The special variable * 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 = 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 ($) operator:


       Any variable which has not been assigned a value returns the null list,
       (), when referenced.  Multiple references are allowed:

            a = foo
            b = a
            echo $ $ b



       A variable's definition may also be removed by assigning the null list
       to a variable:


       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 (_) and star (*).  To reference a variable with other
       characters in its name, quote the variable name.  Thus:

            echo $'we$Ird:Variab!le'

   Local Variables
       Any number of variable assignments may be made local to a single
       command by typing:

            a=foo b=bar ... command

       The command may be a compound command, so for example:

            path=. ifs=() {

       sets path to .  and removes ifs for the duration of one long compound

   Variable Subscripts
       Variables may be subscripted with the notation


       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)
            echo $a(3 3 3)


            three three three

       If n references a nonexistent element, then $var(n) returns the null
       list.  The notation $n, where n is an integer, is a shorthand for
       $*(n).  Thus, rc's arguments may be referred to as $1, $2, and so on.

       Note also that the list of subscripts may be given by any of rc's list

            $var(`{awk 'BEGIN{for(i=1;i<=10;i++)print i;exit; }'})

       returns the first 10 elements of $var.

       To count the number of elements in a variable, use


       This returns a single-element list, with the number of elements in

   Flat Lists
       In order to create a single-element list from a multi-element list,
       with the components space-separated, use the dollar-caret ($^)


       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,

            echo $^path.

       For compability with the Plan 9 rc,


       is accepted as a synonym for dollar-caret.

   Backquote Substitution
       A list may be formed from the output of a command by using backquote

            `{ command }

       returns a list formed from the standard output of the command in
       braces.  $ifs is used to split the output into list elements.  By
       default, $ifs has the value space-tab-newline.  The braces may be
       omitted if the command is a single word.  Thus `ls may be used instead
       of `{ls}.  This last feature is useful when defining functions that
       expand to useful argument lists.  A frequent use is:

            fn src { echo *.[chy] }

       followed by

            wc `src

       (This will print out a word-count of all C source files in the current

       In order to override the value of $ifs for a single backquote
       substitution, use:

            `` (ifs-list) { command }

       $ifs 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}

       splits up /etc/passwd into fields, assuming that $nl contains a newline
       as its value.

       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 $cdpath causes an automatic
       assignment to $CDPATH, and vice-versa.  If $CDPATH is set when rc is
       started, its value is imported into $cdpath.  $cdpath and $path are rc
       lists; $CDPATH and $PATH are colon-separated lists.  Only the names
       spelt in capitals are exported into the environment.

       * (no-export)
              The argument list of rc.  $1, $2, etc. are the same as $*(1),
              $*(2), etc.

       0 (default no-export)
              The variable $0 holds the value of argv[0] with which rc was
              invoked.  Additionally, $0 is set to the name of a function for
              the duration of the execution of that function, and $0 is also
              set to the name of the file being interpreted for the duration
              of a .  command.  $0 is not an element of $*, and is never
              treated as one.

       apid (no-export)
              The process ID of the last process started in the background.

       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.

       bqstatus (no-export)
              The exit status of the rc forked to execute the most recent
              backquote substitution.  Note that, unlike $status, $bqstatus is
              always a single element list (see EXIT STATUS below).  For

                   echo foo |grep bar; whatis status


                   status=(0 1)


                   x=`{echo foo |grep bar}; whatis bqstatus



       cdpath (alias)
              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 $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.

              $history 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 $history is not set, then rc does not
              append commands to any file.

       home (alias)
              The default directory for the builtin cd command, and the
              directory in which rc looks to find its initialization file,
              .rcrc, if rc has been started up as a login shell.

       ifs (default)
              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.

       path (alias)
              This is a list of directories to search in for commands.  The
              empty string stands for the current directory.  If neither $PATH
              nor $path is set at startup time, $path assumes a default value
              suitable for your system.  This is typically (/usr/local/bin
              /usr/bin /usr/ucb /bin .)

       pid (default no-export)
              On startup, $pid is initialized to the numeric process ID of the
              currently running rc.

       prompt (default)
              This variable holds the two prompts (in list form, of course)
              that rc prints.  $prompt(1) is printed before each command is
              read, and $prompt(2) is printed when input is expected to
              continue on the next line.  rc sets $prompt to ('; ' '') 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) also has its justification:
              an rc script, when typed interactively, will not leave
              $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.

       prompt (function)
              If this function is defined, then it gets executed every time rc
              is about to print $prompt(1).

       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 ``+core'' is appended.  The value
              of $status for a pipeline is a list, with one entry, as above,
              for each process in the pipeline.  For example, the command

                   ls | wc

              usually sets $status to (0 0).

       version (default)
              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).

       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 }

       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 name

       (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, $* is set to the arguments to that function for the duration
       of the command.  Thus a reasonable definition for l, a shorthand for
       ls(1), could be:

            fn l { ls -FC $* }

       but not

            fn l { ls -FC } # WRONG

       rc recognizes a number of signals, and allows the user to define shell
       functions which act as signal handlers.  rc by default traps SIGINT
       when it is in interactive mode.  SIGQUIT and SIGTERM are ignored,
       unless rc has been invoked with the -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:

            fn sighup { echo hangup; rm /tmp/rc$pid.*; exit }

       In addition to Unix signals, rc recognizes the artificial signal
       SIGEXIT 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 sigint

       returns the handler of SIGINT to the default value.  In order to ignore
       a signal, set the signal handler's value to {}.  Thus:

            fn sigint {}

       causes SIGINT to be ignored by the shell.  Only signals that are being
       ignored are passed on to programs run by rc; signal functions are not

       On System V-based Unix systems, rc will not allow you to trap SIGCLD.

       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 -i
              flag, input is interactive.  Thus from within a shell script,

                   . -i /dev/tty

              does the ``right thing''.

       break  Breaks from the innermost for or while, as in C.  It is an error
              to invoke break outside of a loop.  (Note that there is no break
              keyword between commands in switch 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 $* }

              is a reasonable way to pass a default set of arguments to ls(1),

                   fn ls { ls -FC $* } # WRONG

              is a non-terminating recursion, which will cause rc to exhaust
              its stack space and (eventually) terminate if it is executed.

       cd [directory]
              Changes the current directory to directory.  The variable
              $cdpath is searched for possible locations of directory,
              analogous to the searching of $path for executable files.  With
              no argument, cd changes the current directory to $home.

       echo [-n] [--] [arg ...]
              Prints its arguments to standard output, terminated by a
              newline.  Arguments are separated by spaces.  If the first
              argument is -n no final newline is printed.  If the first
              argument is --, then all other arguments are echoed literally.
              This is used for echoing a literal -n.

       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.out

              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 $status is used.

       limit [-h] [resource [value]]
              Similar to the csh(1) limit builtin, this command operates upon
              the BSD-style resource limits of a process.  The -h 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

                   limit coredumpsize 0

              disables core dumps.  To set a soft limit equal to the hard

                   limit `{limit -h datasize}

              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)

              (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 $status is left unchanged.  It is an error to
              invoke return when not inside a function.

       shift [n]
              Deletes n elements from the beginning of $* 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, builtin
              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.)  Without arguments, whatis is equivalent to
              whatis -fv, and prints the values of all shell variables and

              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 .
              command.  Another note: whatis -s > file 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().

              Since whatis uses getopt(3) to parse its arguments, you can use
              the special argument -- to terminate its flags.  This allows you
              to use names beginning with a dash, such as the history(1)
              commands.  For example,

                   whatis -- -p

       The shift builtin only shifts $*.  This function can shift any variable
       (except $lshift).

            fn lshift { lshift=$*; *=$$1; shift $lshift(2); $lshift(1)=$* }

       With this definition in place,

            walrus = (shoes ships sealing-wax cabbages kings)
            lshift walrus 3
            whatis walrus


            walrus=(cabbages kings)

       The $^var operator flattens a list by separating each element with a
       space.  This function allows the separator to be an arbitrary string.

            fn lflat {
              lflat=$*; *=$$1
              while () {
                echo -n $1; shift
                ~ $#* 0 && break
                echo -n $lflat(2)

       With this definition in place,

            hops=(uunet mcvax ukc tlg)
            lflat hops !

       prints (with no final newline)


       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 0 if every
       command in the pipeline did; otherwise it exits 1.

       rc can be made to exit with a particular status using the exit builtin.

       Here is rc's grammar, edited to remove semantic actions.


            %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 '=' 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 */ | '^'

            simple: first | simple word | simple redir

            first: comword | first '^' sword

            sword: comword | keyword

            word: sword | word '^' sword

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

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

            words: /* empty */ | words word

            optnl: /* empty */ | optnl '\n'

       $HOME/.rcrc, /tmp/rc*, /dev/null

       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.

       There is a compile-time limit on the number of ; separated commands in
       a line: usually 500.  This is sometimes a problem for automatically
       generated scripts: substituting the newline character for ; avoids the

       On modern systems that support /dev/fd or /proc/self/fd, <{foo} 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 /tmp 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/fd 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 ~ expression or a !  expression are a syntax
       error.  Thus, this code is illegal.

            while ((~ $1 -*) && (! ~ $1 --)) { ...

       The redundant inner parentheses must be omitted.

       Variable subscripting cannot be used in here documents.

       The limit 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 }
            x=(a b) # NOT x=(a '' b)

       Bug reports should be mailed to

       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 .  file, the Tenth Edition rc searches $path for file.  This rc
       does not, since it is not considered useful.

       The list flattening operator, $^foo, is spelt $"foo in those versions
       of the Bell Labs rc which have it.

       The following are all new with this version of rc: The -n flag, here
       strings (they facilitate exporting of functions with here documents
       into the environment), the return and break keywords, the echo builtin,
       the bqstatus and version variables, the support for the GNU readline(3)
       library, and the support for the prompt function.  This rc also sets $0
       to the name of a function being executed/file being sourced.

       ``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, an updated version of the
       above paper.


                                  2015-05-13                             RC(1)