GNU.WIKI: The GNU/Linux Knowledge Base

  [HOME] [PHP Manual] [HowTo] [ABS] [MAN1] [MAN2] [MAN3] [MAN4] [MAN5] [MAN6] [MAN7] [MAN8] [MAN9]

  [0-9] [Aa] [Bb] [Cc] [Dd] [Ee] [Ff] [Gg] [Hh] [Ii] [Jj] [Kk] [Ll] [Mm] [Nn] [Oo] [Pp] [Qq] [Rr] [Ss] [Tt] [Uu] [Vv] [Ww] [Xx] [Yy] [Zz]


       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

            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

            ! 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.

   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 '
            %left BANG SUBSHELL
            %left PIPE
            %right '$'
            %left SUB

            %start rc


            rc: line end
                 | error end

            end: END /* EOF */ | '

            cmdsa: cmd ';' | cmd '&'

            line: cmd | cmdsa line

            body: cmd | cmdsan body

            cmdsan: cmdsa | cmd '

            brace: '{' body '}'

            paren: '(' body ')'

            assign: first '=' word

            epilog: /* empty */ | redir epilog

            redir: DUP | REDIR word

            case: CASE words ';' | CASE words '

            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 '


       $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.

       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),  an  updated  version  of the
       above paper.


                                  2003-07-17                             RC(1)

  All copyrights belong to their respective owners. Other content (c) 2014-2018, GNU.WIKI. Please report site errors to
Page load time: 0.088 seconds. Last modified: November 04 2018 12:49:43.