Provided by: rc_1.7.1-3_i386 bug

NAME

       rc - shell

SYNOPSIS

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

DESCRIPTION

       rc  is a command interpreter and programming language similar to sh(1).
       It is based on the AT&T Plan 9 shell  of  the  same  name.   The  shell
       offers  a C-like syntax (much more so than the C shell), and a powerful
       mechanism for manipulating  variables.   It  is  reasonably  small  and
       reasonably  fast, especially when compared to contemporary shells.  Its
       use is intended to be interactive, but the language lends  itself  well
       to scripts.

OPTIONS

       -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
              SIGINT.

       -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
              apply.)

       -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
              read.

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

COMMANDS

       A simple command is a sequence  of  words,  separated  by  white  space
       (space  and tab) characters that ends with a newline, semicolon (;), 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.

   Subshells
       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.)

   Quoting
       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.

   Grouping
       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
            } | 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
       braces:

            {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
       sequence

            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

            $variable^follow

       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
       useful.)

   Pipes
       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 /’}

CONTROL STRUCTURES

       The following may be used for control flow in rc:

   If-Else Statements
       if (test) {
           cmd
       } 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)
                       command

   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
              example:

                   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
       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
       Unix).

            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.

PATTERN MATCHING

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

            command argument argument ...

       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,

            foo=’*’
            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.

LISTS AND VARIABLES

       The primary data structure in rc is the list, which is  a  sequence  of
       words.   Parentheses  are  used  to  group  lists.   The  empty list is
       represented by ().  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

            foobar

   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.

   Variables
       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:

            $var

       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

       prints

            foo

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

            var=()

       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
       command.

   Variable Subscripts
       Variables may be subscripted with the notation

            $var(n)

       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)

       prints

            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
       operations:

            $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

            $#var

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

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

            $^var

       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,
       use:

            echo $^path.

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

            `{ 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
       directory.)

       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.

SPECIAL VARIABLES

       Several variables are known to rc and are treated  specially.   In  the
       following  list,  ‘‘default’’  indicates  that  rc gives the variable a
       default value on startup; ‘‘no-export’’ indicates that the variable  is
       never  exported; and ‘‘read-only’’ indicates that an attempt to set the
       variable will silently have no effect.

       Also, ‘‘alias’’ means that the variable is aliased to the same name  in
       capitals.   For  example,  an assignment to $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
              example:

                   echo foo |grep bar; whatis status

              prints

                   status=(0 1)

              whereas

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

              prints

                   bqstatus=1

       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
              $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).

FUNCTIONS

       rc functions are identical to rc scripts, except that they  are  stored
       in memory and are automatically exported into the environment.  A shell
       function is declared as:

            fn name { commands }

       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

INTERRUPTS AND SIGNALS

       rc  recognizes a number of signals, and allows the user to define shell
       functions which act as signal handlers.  rc  by  default  traps  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
       exported.

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

BUILTIN COMMANDS

       Builtin commands execute in the context of  the  shell,  but  otherwise
       behave  exactly  like  other  commands.   Although  !,  ~ and @ are not
       strictly speaking builtin commands, they can usually be used as such.

       . [-i] file [arg ...]
              Reads file as input to rc and executes its contents.  With a  -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),
              whereas

                   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
              example:

                   limit coredumpsize 0

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

                   limit ‘{limit -h datasize}

       newpgrp
              Puts  rc  into  a new process group.  This builtin is useful for
              making  rc  behave  like  a  job-control  shell  in  a   hostile
              environment.   One  example  is the NeXT Terminal program, which
              implicitly assumes that each shell it forks will put itself into
              a new process group.

       return [n]
              Returns  from  the current function, with status n, where n is a
              valid exit status, or a list of them.  Thus it is legal to have

                   return (sigpipe 1 2 3)

              (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
              functions.

              Note that whatis output is suitable for input to rc;  by  saving
              the  output  of  whatis  in  a  file,  it  should be possible to
              recreate the state  of  rc  by  sourcing  this  file  with  a  .
              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

EXAMPLES

       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

       prints

            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)

            uunet!mcvax!ukc!tlg

EXIT STATUS

       The  exit status of rc is normally the same as that of the last command
       executed.  If the last command was a pipeline,  rc  exits  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.

GRAMMAR

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

            %term ANDAND BACKBACK BANG CASE COUNT DUP ELSE END FLAT FN FOR IF IN
            %term OROR PIPE REDIR SUB SUBSHELL SWITCH TWIDDLE WHILE WORD HUH

            %left 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’

FILES

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

CREDITS

       rc was written by Byron Rakitzis, with valuable help from  Paul  Haahr,
       Hugh  Redelmeier  and  David  Sanderson.   The design of this shell was
       copied from the rc that Tom Duff wrote at Bell Labs.

BUGS

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

       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.

       Bug reports should be mailed to <tjg@star.le.ac.uk>.

INCOMPATIBILITIES

       Here is a list of features which distinguish  this  incarnation  of  rc
       from the one described in the Bell Labs manual pages:

       The  Tenth  Edition  rc does not have the else keyword.  Instead, if is
       optionally followed by an if  not  clause  which  is  executed  if  the
       preceding if test does not succeed.

       Backquotes are slightly different in Tenth Edition rc: a backquote must
       always be followed by a left-brace.  This restriction  is  not  present
       for single-word commands in this rc.

       For  .   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.

SEE ALSO

       ‘‘rc — A Shell for Plan 9 and UNIX  Systems’’,  Unix  Research  System,
       Tenth Edition, Volume 2. (Saunders College Publishing)

       http://www.star.le.ac.uk/~tjg/rc/misc/td,  an  updated  version  of the
       above paper.

       history(1)

                                  2003-07-17                             RC(1)