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CSH(1)                       UNIX Reference Manual                      CSH(1)

N✓NA✓AM✓ME✓E
     c✓cs✓sh✓h - a shell (command interpreter) with C-like syntax

S✓SY✓YN✓NO✓OP✓PS✓SI✓IS✓S
     c✓cs✓sh✓h [-✓-b✓bc✓ce✓ef✓fi✓in✓ns✓st✓tv✓vV✓Vx✓xX✓X] [arg ...]

D✓DE✓ES✓SC✓CR✓RI✓IP✓PT✓TI✓IO✓ON✓N
     The C✓Cs✓sh✓h is a command language interpreter incorporating a history mecha-
     nism (see H✓Hi✓is✓st✓to✓or✓ry✓y S✓Su✓ub✓bs✓st✓ti✓it✓tu✓ut✓ti✓io✓on✓ns✓s), job control facilities (see J✓Jo✓ob✓bs✓s), in-
     teractive file name and user name completion (see F✓Fi✓il✓le✓e N✓Na✓am✓me✓e C✓Co✓om✓mp✓pl✓le✓et✓ti✓io✓on✓n),
     and a C-like syntax. It is used both as an interactive login shell and a
     shell script command processor.

   A✓Ar✓rg✓gu✓um✓me✓en✓nt✓t l✓li✓is✓st✓t p✓pr✓ro✓oc✓ce✓es✓ss✓si✓in✓ng✓g
     If the first argument (argument 0) to the shell is `-✓-' then this is a lo-
     gin shell.  The flag arguments are interpreted as follows:

     -✓-b✓b     This flag forces a ``break'' from option processing, causing any
            further shell arguments to be treated as non-option arguments.
            The remaining arguments will not be interpreted as shell options.
            This may be used to pass options to a shell script without confu-
            sion or possible subterfuge.  The shell will not run a set-user ID
            script without this option.

     -✓-c✓c     Commands are read from the (single) following argument which must
            be present.  Any remaining arguments are placed in _✓a_✓r_✓g_✓v.

     -✓-e✓e     The shell exits if any invoked command terminates abnormally or
            yields a non-zero exit status.

     -✓-f✓f     The shell will start faster, because it will neither search for
            nor execute commands from the file _✓._✓c_✓s_✓h_✓r_✓c in the invoker's home
            directory.

     -✓-i✓i     The shell is interactive and prompts for its top-level input, even
            if it appears to not be a terminal.  Shells are interactive with-
            out this option if their inputs and outputs are terminals.

     -✓-n✓n     Commands are parsed, but not executed.  This aids in syntactic
            checking of shell scripts.

     -✓-s✓s     Command input is taken from the standard input.

     -✓-t✓t     A single line of input is read and executed.  A `\' may be used to
            escape the newline at the end of this line and continue onto an-
            other line.

     -✓-v✓v     Causes the _✓v_✓e_✓r_✓b_✓o_✓s_✓e variable to be set, with the effect that com-
            mand input is echoed after history substitution.

     -✓-x✓x     Causes the _✓e_✓c_✓h_✓o variable to be set, so that commands are echoed
            immediately before execution.

     -✓-V✓V     Causes the _✓v_✓e_✓r_✓b_✓o_✓s_✓e variable to be set even before _✓._✓c_✓s_✓h_✓r_✓c is exe-
            cuted.

     -✓-X✓X     Is to -✓-x✓x as -✓-V✓V is to -✓-v✓v.

     After processing of flag arguments, if arguments remain but none of the
     -✓-c✓c, -✓-i✓i, -✓-s✓s, or -✓-t✓t options were given, the first argument is taken as the
     name of a file of commands to be executed.  The shell opens this file,
     and saves its name for possible resubstitution by `$0'.  Since many sys-
     tems use either the standard version 6 or version 7 shells whose shell
     scripts are not compatible with this shell, the shell will execute such a
     `standard' shell if the first character of a script is not a `#', i.e. if
     the script does not start with a comment.  Remaining arguments initialize
     the variable _✓a_✓r_✓g_✓v.

     An instance of c✓cs✓sh✓h begins by executing commands from the file
     _✓/_✓e_✓t_✓c_✓/_✓c_✓s_✓h_✓._✓c_✓s_✓h_✓r_✓c and, if this is a login shell, _✓/_✓e_✓t_✓c_✓/_✓c_✓s_✓h_✓._✓l_✓o_✓g_✓i_✓n. It then ex-
     ecutes commands from _✓._✓c_✓s_✓h_✓r_✓c in the _✓h_✓o_✓m_✓e directory of the invoker, and, if
     this is a login shell, the file _✓._✓l_✓o_✓g_✓i_✓n in the same location.  It is typi-
     cal for users on crt's to put the command ``stty crt'' in their _✓._✓l_✓o_✓g_✓i_✓n
     file, and to also invoke tset(1) there.

     In the normal case, the shell will begin reading commands from the termi-
     nal, prompting with `% '.  Processing of arguments and the use of the
     shell to process files containing command scripts will be described lat-
     er.

     The shell repeatedly performs the following actions: a line of command
     input is read and broken into _✓w_✓o_✓r_✓d_✓s. This sequence of words is placed on
     the command history list and parsed.  Finally each command in the current
     line is executed.

     When a login shell terminates it executes commands from the files _✓._✓l_✓o_✓g_✓o_✓u_✓t
     in the user's _✓h_✓o_✓m_✓e directory and _✓/_✓e_✓t_✓c_✓/_✓c_✓s_✓h_✓._✓l_✓o_✓g_✓o_✓u_✓t.

   L✓Le✓ex✓xi✓ic✓ca✓al✓l s✓st✓tr✓ru✓uc✓ct✓tu✓ur✓re✓e
     The shell splits input lines into words at blanks and tabs with the fol-
     lowing exceptions.  The characters `&' `|' `;' `<' `>' `(' `)' form sepa-
     rate words.  If doubled in `&&', `||', `<<' or `>>' these pairs form sin-
     gle words.  These parser metacharacters may be made part of other words,
     or prevented their special meaning, by preceding them with `\'.  A new-
     line preceded by a `\' is equivalent to a blank.

     Strings enclosed in matched pairs of quotations, `', ``' or `"', form
     parts of a word; metacharacters in these strings, including blanks and
     tabs, do not form separate words.  These quotations have semantics to be
     described subsequently.  Within pairs of `'' or `"' characters a newline
     preceded by a `\' gives a true newline character.

     When the shell's input is not a terminal, the character `#' introduces a
     comment which continues to the end of the input line.  It is prevented
     this special meaning when preceded by `\' and in quotations using ``',
     `'', and `"'.

   C✓Co✓om✓mm✓ma✓an✓nd✓ds✓s
     A simple command is a sequence of words, the first of which specifies the
     command to be executed.  A simple command or a sequence of simple com-
     mands separated by `|' characters forms a pipeline.  The output of each
     command in a pipeline is connected to the input of the next.  Sequences
     of pipelines may be separated by `;', and are then executed sequentially.
     A sequence of pipelines may be executed without immediately waiting for
     it to terminate by following it with an `&'.

     Any of the above may be placed in `(' `)' to form a simple command (which
     may be a component of a pipeline, etc.)  It is also possible to separate
     pipelines with `||' or `&&' indicating, as in the C language, that the
     second is to be executed only if the first fails or succeeds respective-
     ly. (See _✓E_✓x_✓p_✓r_✓e_✓s_✓s_✓i_✓o_✓n_✓s.)

   J✓Jo✓ob✓bs✓s
     The shell associates a _✓j_✓o_✓b with each pipeline.  It keeps a table of cur-
     rent jobs, printed by the _✓j_✓o_✓b_✓s command, and assigns them small integer
     numbers.  When a job is started asynchronously with `&', the shell prints
     a line which looks like:

           [1] 1234

     indicating that the job which was started asynchronously was job number 1
     and had one (top-level) process, whose process id was 1234.

     If you are running a job and wish to do something else you may hit the
     key ^✓^Z✓Z (control-Z) which sends a STOP signal to the current job.  The
     shell will then normally indicate that the job has been `Stopped', and
     print another prompt.  You can then manipulate the state of this job,
     putting it in the _✓b_✓a_✓c_✓k_✓g_✓r_✓o_✓u_✓n_✓d with the _✓b_✓g command, or run some other com-
     mands and then eventually bring the job back into the foreground with the
     _✓f_✓o_✓r_✓e_✓g_✓r_✓o_✓u_✓n_✓d command _✓f_✓g. A ^✓^Z✓Z takes effect immediately and is like an in-
     terrupt in that pending output and unread input are discarded when it is
     typed.  There is another special key ^✓^Y✓Y which does not generate a STOP
     signal until a program attempts to read(2) it.  This can usefully be
     typed ahead when you have prepared some commands for a job which you wish
     to stop after it has read them.

     A job being run in the background will stop if it tries to read from the
     terminal.  Background jobs are normally allowed to produce output, but
     this can be disabled by giving the command ``stty tostop''.  If you set
     this tty option, then background jobs will stop when they try to produce
     output like they do when they try to read input.

     There are several ways to refer to jobs in the shell.  The character `%'
     introduces a job name.  If you wish to refer to job number 1, you can
     name it as `%1'.  Just naming a job brings it to the foreground; thus
     `%1' is a synonym for `fg %1', bringing job 1 back into the foreground.
     Similarly saying `%1 &' resumes job 1 in the background.  Jobs can also
     be named by prefixes of the string typed in to start them, if these pre-
     fixes are unambiguous, thus `%ex' would normally restart a suspended
     ex(1) job, if there were only one suspended job whose name began with the
     string `ex'.  It is also possible to say `%?string' which specifies a job
     whose text contains _✓s_✓t_✓r_✓i_✓n_✓g, if there is only one such job.

     The shell maintains a notion of the current and previous jobs.  In output
     pertaining to jobs, the current job is marked with a `+' and the previous
     job with a `-'.  The abbreviation `%+' refers to the current job and `%-'
     refers to the previous job.  For close analogy with the syntax of the
     _✓h_✓i_✓s_✓t_✓o_✓r_✓y mechanism (described below), `%%' is also a synonym for the cur-
     rent job.

     The job control mechanism requires that the stty(1) option n✓ne✓ew✓w be set. It
     is an artifact from a _✓n_✓e_✓w implementation of the tty driver which allows
     generation of interrupt characters from the keyboard to tell jobs to
     stop.  See stty(1) for details on setting options in the new tty driver.

   S✓St✓ta✓at✓tu✓us✓s r✓re✓ep✓po✓or✓rt✓ti✓in✓ng✓g
     This shell learns immediately whenever a process changes state.  It nor-
     mally informs you whenever a job becomes blocked so that no further
     progress is possible, but only just before it prints a prompt.  This is
     done so that it does not otherwise disturb your work.  If, however, you
     set the shell variable _✓n_✓o_✓t_✓i_✓f_✓y, the shell will notify you immediately of
     changes of status in background jobs.  There is also a shell command
     _✓n_✓o_✓t_✓i_✓f_✓y which marks a single process so that its status changes will be
     immediately reported.  By default _✓n_✓o_✓t_✓i_✓f_✓y marks the current process; sim-
     ply say `notify' after starting a background job to mark it.

     When you try to leave the shell while jobs are stopped, you will be
     warned that `You have stopped jobs.'  You may use the _✓j_✓o_✓b_✓s command to see
     what they are.  If you do this or immediately try to exit again, the
     shell will not warn you a second time, and the suspended jobs will be
     terminated.

   F✓Fi✓il✓le✓e N✓Na✓am✓me✓e C✓Co✓om✓mp✓pl✓le✓et✓ti✓io✓on✓n
     When the file name completion feature is enabled by setting the shell
     variable _✓f_✓i_✓l_✓e_✓c (see s✓se✓et✓t), c✓cs✓sh✓h will interactively complete file names and
     user names from unique prefixes, when they are input from the terminal
     followed by the escape character (the escape key, or control-[) For exam-
     ple, if the current directory looks like

           DSC.OLD  bin      cmd      lib      xmpl.c
           DSC.NEW  chaosnet cmtest   mail     xmpl.o
           bench    class    dev      mbox     xmpl.out

     and the input is

           % vi ch<escape>

     c✓cs✓sh✓h will complete the prefix ``ch'' to the only matching file name
     ``chaosnet'', changing the input line to

           % vi chaosnet

     However, given

           % vi D<escape>

     c✓cs✓sh✓h will only expand the input to

           % vi DSC.

     and will sound the terminal bell to indicate that the expansion is incom-
     plete, since there are two file names matching the prefix ``D''.

     If a partial file name is followed by the end-of-file character (usually
     control-D), then, instead of completing the name, c✓cs✓sh✓h will list all file
     names matching the prefix.  For example, the input

           % vi D<control-D>

     causes all files beginning with ``D'' to be listed:

           DSC.NEW   DSC.OLD

     while the input line remains unchanged.

     The same system of escape and end-of-file can also be used to expand par-
     tial user names, if the word to be completed (or listed) begins with the
     character ``~''.  For example, typing

           cd ~ro<escape>

     may produce the expansion

           cd ~root

     The use of the terminal bell to signal errors or multiple matches can be
     inhibited by setting the variable _✓n_✓o_✓b_✓e_✓e_✓p.

     Normally, all files in the particular directory are candidates for name
     completion.  Files with certain suffixes can be excluded from considera-
     tion by setting the variable _✓f_✓i_✓g_✓n_✓o_✓r_✓e to the list of suffixes to be ig-
     nored.  Thus, if _✓f_✓i_✓g_✓n_✓o_✓r_✓e is set by the command

           % set fignore = (.o .out)

     then typing

           % vi x<escape>


     would result in the completion to

           % vi xmpl.c

     ignoring the files "xmpl.o" and "xmpl.out".  However, if the only comple-
     tion possible requires not ignoring these suffixes, then they are not ig-
     nored.  In addition, _✓f_✓i_✓g_✓n_✓o_✓r_✓e does not affect the listing of file names by
     control-D.  All files are listed regardless of their suffixes.

   S✓Su✓ub✓bs✓st✓ti✓it✓tu✓ut✓ti✓io✓on✓ns✓s
     We now describe the various transformations the shell performs on the in-
     put in the order in which they occur.

   H✓Hi✓is✓st✓to✓or✓ry✓y s✓su✓ub✓bs✓st✓ti✓it✓tu✓ut✓ti✓io✓on✓ns✓s
     History substitutions place words from previous command input as portions
     of new commands, making it easy to repeat commands, repeat arguments of a
     previous command in the current command, or fix spelling mistakes in the
     previous command with little typing and a high degree of confidence.
     History substitutions begin with the character `!' and may begin _✓a_✓n_✓y_✓w_✓h_✓e_✓r_✓e
     in the input stream (with the proviso that they d✓do✓o n✓no✓ot✓t nest.)  This `!'
     may be preceded by an `\' to prevent its special meaning; for conve-
     nience, a `!' is passed unchanged when it is followed by a blank, tab,
     newline, `=' or `('.  (History substitutions also occur when an input
     line begins with `^'.  This special abbreviation will be described lat-
     er.)  Any input line which contains history substitution is echoed on the
     terminal before it is executed as it could have been typed without histo-
     ry substitution.

     Commands input from the terminal which consist of one or more words are
     saved on the history list.  The history substitutions reintroduce se-
     quences of words from these saved commands into the input stream.  The
     size of which is controlled by the _✓h_✓i_✓s_✓t_✓o_✓r_✓y variable; the previous command
     is always retained, regardless of its value.  Commands are numbered se-
     quentially from 1.

     For definiteness, consider the following output from the _✓h_✓i_✓s_✓t_✓o_✓r_✓y command:

            9  write michael
           10  ex write.c
           11  cat oldwrite.c
           12  diff *write.c

     The commands are shown with their event numbers.  It is not usually nec-
     essary to use event numbers, but the current event number can be made
     part of the _✓p_✓r_✓o_✓m_✓p_✓t by placing an `!' in the prompt string.

     With the current event 13 we can refer to previous events by event number
     `!11', relatively as in `!-2' (referring to the same event), by a prefix
     of a command word as in `!d' for event 12 or `!wri' for event 9, or by a
     string contained in a word in the command as in `!?mic?' also referring
     to event 9.  These forms, without further modification, simply reintro-
     duce the words of the specified events, each separated by a single blank.
     As a special case `!!' refers to the previous command; thus `!!'  alone
     is essentially a _✓r_✓e_✓d_✓o.

     To select words from an event we can follow the event specification by a
     `:' and a designator for the desired words.  The words of an input line
     are numbered from 0, the first (usually command) word being 0, the second
     word (first argument) being 1, etc.  The basic word designators are:

           0       first (command) word
           _✓n       _✓n'th argument
           ^       first argument,  i.e. `1'
           $       last argument
           %       word matched by (immediately preceding)

                   ?_✓s.             rm S0 search
           _✓x_✓-_✓y     range of words
           _✓-_✓y      abbreviates _✓`_✓0_✓-_✓y_✓'
           *       abbreviates `^-$', or nothing if only 1 word in event
           _✓x_✓*      abbreviates _✓`_✓x_✓-_✓$_✓'
           _✓x_✓-      like _✓`_✓x_✓*_✓' but omitting word `$'

     The `:' separating the event specification from the word designator can
     be omitted if the argument selector begins with a `^', `$', `*' `-' or
     `%'.  After the optional word designator can be placed a sequence of mod-
     ifiers, each preceded by a `:'.  The following modifiers are defined:

           h       Remove a trailing pathname component, leaving the head.
           r       Remove a trailing `.xxx' component, leaving the root name.
           e       Remove all but the extension `.xxx' part.
           s_✓/_✓l_✓/_✓r_✓/  Substitute _✓l for _✓r
           t       Remove all leading pathname components, leaving the tail.
           &       Repeat the previous substitution.
           g       Apply the change globally, prefixing the above, e.g. `g&'.
           p       Print the new command line but do not execute it.
           q       Quote the substituted words, preventing further substitu-
                   tions.
           x       Like q, but break into words at blanks, tabs and newlines.

     Unless preceded by a `g' the modification is applied only to the first
     modifiable word.  With substitutions, it is an error for no word to be
     applicable.

     The left hand side of substitutions are not regular expressions in the
     sense of the editors, but rather strings.  Any character may be used as
     the delimiter in place of `/'; a `\' quotes the delimiter into the _✓l and
     _✓r strings.  The character `&' in the right hand side is replaced by the
     text from the left.  A `\' quotes `&' also.  A null _✓l (" ") uses the pre-
     vious string either from a _✓l or from a contextual scan string _✓s in `!?  _✓s
     The trailing delimiter in the substitution may be omitted if a newline
     follows immediately as may the trailing `?' in a contextual scan.

     A history reference may be given without an event specification, e.g.
     `!$'.  In this case the reference is to the previous command unless a
     previous history reference occurred on the same line in which case this
     form repeats the previous reference.  Thus `!?foo?^ !$' gives the first
     and last arguments from the command matching `?foo?'.

     A special abbreviation of a history reference occurs when the first non-
     blank character of an input line is a `^'.  This is equivalent to `!:s^'
     providing a convenient shorthand for substitutions on the text of the
     previous line.  Thus `^lb^lib' fixes the spelling of `lib' in the previ-
     ous command.  Finally, a history substitution may be surrounded with `{'
     and `}' if necessary to insulate it from the characters which follow.
     Thus, after `ls -ld ~paul' we might do `!{l}a' to do `ls -ld ~paula',
     while `!la' would look for a command starting `la'.

   Q✓Qu✓uo✓ot✓ta✓at✓ti✓io✓on✓ns✓s w✓wi✓it✓th✓h '✓' a✓an✓nd✓d "✓"
     The quotation of strings by `'' and `"' can be used to prevent all or
     some of the remaining substitutions.  Strings enclosed in `'' are pre-
     vented any further interpretation.  Strings enclosed in `"' may be ex-
     panded as described below.

     In both cases the resulting text becomes (all or part of) a single word;
     only in one special case (see _✓C_✓o_✓m_✓m_✓a_✓n_✓d _✓S_✓u_✓b_✓s_✓t_✓i_✓t_✓i_✓t_✓i_✓o_✓n below) does a `"'
     quoted string yield parts of more than one word; `'' quoted strings never
     do.

   A✓Al✓li✓ia✓as✓s s✓su✓ub✓bs✓st✓ti✓it✓tu✓ut✓ti✓io✓on✓n
     The shell maintains a list of aliases which can be established, displayed
     and modified by the _✓a_✓l_✓i_✓a_✓s and _✓u_✓n_✓a_✓l_✓i_✓a_✓s commands.  After a command line is
     scanned, it is parsed into distinct commands and the first word of each
     command, left-to-right, is checked to see if it has an alias.  If it
     does, then the text which is the alias for that command is reread with
     the history mechanism available as though that command were the previous
     input line.  The resulting words replace the command and argument list.
     If no reference is made to the history list, then the argument list is
     left unchanged.

     Thus if the alias for `ls' is `ls -l' the command `ls /usr' would map to
     `ls -l /usr', the argument list here being undisturbed.  Similarly if the
     alias for `lookup' was `grep !^ /etc/passwd' then `lookup bill' would map
     to `grep bill /etc/passwd'.

     If an alias is found, the word transformation of the input text is per-
     formed and the aliasing process begins again on the reformed input line.
     Looping is prevented if the first word of the new text is the same as the
     old by flagging it to prevent further aliasing.  Other loops are detected
     and cause an error.

     Note that the mechanism allows aliases to introduce parser metasyntax.
     Thus we can `alias print 'pr \!* | lpr'' to make a command which _✓p_✓r _✓'_✓s
     its arguments to the line printer.

   V✓Va✓ar✓ri✓ia✓ab✓bl✓le✓e s✓su✓ub✓bs✓st✓ti✓it✓tu✓ut✓ti✓io✓on✓n
     The shell maintains a set of variables, each of which has as value a list
     of zero or more words.  Some of these variables are set by the shell or
     referred to by it.  For instance, the _✓a_✓r_✓g_✓v variable is an image of the
     shell's argument list, and words of this variable's value are referred to
     in special ways.

     The values of variables may be displayed and changed by using the _✓s_✓e_✓t and
     _✓u_✓n_✓s_✓e_✓t commands.  Of the variables referred to by the shell a number are
     toggles; the shell does not care what their value is, only whether they
     are set or not.  For instance, the _✓v_✓e_✓r_✓b_✓o_✓s_✓e variable is a toggle which
     causes command input to be echoed.  The setting of this variable results
     from the -✓-v✓v command line option.

     Other operations treat variables numerically.  The `@' command permits
     numeric calculations to be performed and the result assigned to a vari-
     able.  Variable values are, however, always represented as (zero or more)
     strings.  For the purposes of numeric operations, the null string is con-
     sidered to be zero, and the second and subsequent words of multiword val-
     ues are ignored.

     After the input line is aliased and parsed, and before each command is
     executed, variable substitution is performed keyed by `$' characters.
     This expansion can be prevented by preceding the `$' with a `\' except
     within `"'s where it _✓a_✓l_✓w_✓a_✓y_✓s occurs, and within `''s where it _✓n_✓e_✓v_✓e_✓r oc-
     curs.  Strings quoted by ``' are interpreted later (see C✓Co✓om✓mm✓ma✓an✓nd✓d
     s✓su✓ub✓bs✓st✓ti✓it✓tu✓ut✓ti✓io✓on✓n below) so `$' substitution does not occur there until later,
     if at all.  A `$' is passed unchanged if followed by a blank, tab, or
     end-of-line.

     Input/output redirections are recognized before variable expansion, and
     are variable expanded separately.  Otherwise, the command name and entire
     argument list are expanded together.  It is thus possible for the first
     (command) word to this point to generate more than one word, the first of
     which becomes the command name, and the rest of which become arguments.

     Unless enclosed in `"' or given the `:q' modifier the results of variable
     substitution may eventually be command and filename substituted.  Within
     `"', a variable whose value consists of multiple words expands to a (por-
     tion of) a single word, with the words of the variables value separated
     by blanks.  When the `:q' modifier is applied to a substitution the vari-
     able will expand to multiple words with each word separated by a blank
     and quoted to prevent later command or filename substitution.

     The following metasequences are provided for introducing variable values
     into the shell input.  Except as noted, it is an error to reference a
     variable which is not set.

           $name
           ${name}
                   Are replaced by the words of the value of variable _✓n_✓a_✓m_✓e,
                   each separated by a blank.  Braces insulate _✓n_✓a_✓m_✓e from fol-
                   lowing characters which would otherwise be part of it.
                   Shell variables have names consisting of up to 20 letters
                   and digits starting with a letter.  The underscore charac-
                   ter is considered a letter.
                   If _✓n_✓a_✓m_✓e is not a shell variable, but is set in the environ-
                   ment, then that value is returned (but : modifiers and the
                   other forms given below are not available in this case).
           $name[selector]
           ${name[selector}]
                   May be used to select only some of the words from the value
                   of _✓n_✓a_✓m_✓e. The selector is subjected to `$' substitution and
                   may consist of a single number or two numbers separated by
                   a `-'.  The first word of a variables value is numbered
                   `1'.  If the first number of a range is omitted it defaults
                   to `1'.  If the last member of a range is omitted it de-
                   faults to `$#name'.  The selector `*' selects all words.
                   It is not an error for a range to be empty if the second
                   argument is omitted or in range.
           $#name
           ${#name}
                   Gives the number of words in the variable.  This is useful
                   for later use in a `$argv[selector]'.
           $0      Substitutes the name of the file from which command input
                   is being read.  An error occurs if the name is not known.
           $number
           ${number}
                   Equivalent to `$argv[number]'.
           $*      Equivalent to `$argv[*]'.  The modifiers `:e', `:h', `:t',
                   `:r', `:q' and `:x' may be applied to the substitutions
                   above as may `:gh', `:gt' and `:gr'.  If braces `{' '}' ap-
                   pear in the command form then the modifiers must appear
                   within the braces.  The current implementation allows only
                   one `:' modifier on each `$' expansion.

     The following substitutions may not be modified with `:' modifiers.
           $?name
           ${?name}
                   Substitutes the string `1' if name is set, `0' if it is
                   not.
           $?0     Substitutes `1' if the current input filename is known, `0'
                   if it is not.
                   Substitute the (decimal) process number of the (parent)
                   shell.
           $<      Substitutes a line from the standard input, with no further
                   interpretation thereafter.  It can be used to read from the
                   keyboard in a shell script.

   C✓Co✓om✓mm✓ma✓an✓nd✓d a✓an✓nd✓d f✓fi✓il✓le✓en✓na✓am✓me✓e s✓su✓ub✓bs✓st✓ti✓it✓tu✓ut✓ti✓io✓on✓n
     The remaining substitutions, command and filename substitution, are ap-
     plied selectively to the arguments of builtin commands.  This means that
     portions of expressions which are not evaluated are not subjected to
     these expansions.  For commands which are not internal to the shell, the
     command name is substituted separately from the argument list.  This oc-
     curs very late, after input-output redirection is performed, and in a
     child of the main shell.


   C✓Co✓om✓mm✓ma✓an✓nd✓d s✓su✓ub✓bs✓st✓ti✓it✓tu✓ut✓ti✓io✓on✓n
     Command substitution is indicated by a command enclosed in ``'.  The out-
     put from such a command is normally broken into separate words at blanks,
     tabs and newlines, with null words being discarded, this text then re-
     placing the original string.  Within `"'s, only newlines force new words;
     blanks and tabs are preserved.

     In any case, the single final newline does not force a new word.  Note
     that it is thus possible for a command substitution to yield only part of
     a word, even if the command outputs a complete line.

   F✓Fi✓il✓le✓en✓na✓am✓me✓e s✓su✓ub✓bs✓st✓ti✓it✓tu✓ut✓ti✓io✓on✓n
     If a word contains any of the characters `*', `?', `[' or `{' or begins
     with the character `~', then that word is a candidate for filename sub-
     stitution, also known as `globbing'.  This word is then regarded as a
     pattern, and replaced with an alphabetically sorted list of file names
     which match the pattern.  In a list of words specifying filename substi-
     tution it is an error for no pattern to match an existing file name, but
     it is not required for each pattern to match.  Only the metacharacters
     `*', `?' and `[' imply pattern matching, the characters `~' and `{' being
     more akin to abbreviations.

     In matching filenames, the character `.' at the beginning of a filename
     or immediately following a `/', as well as the character `/' must be
     matched explicitly.  The character `*' matches any string of characters,
     including the null string.  The character `?' matches any single charac-
     ter.  The sequence `[...]' matches any one of the characters enclosed.
     Within `[...]', a pair of characters separated by `-' matches any charac-
     ter lexically between the two.

     The character `~' at the beginning of a filename is used to refer to home
     directories.  Standing alone, i.e. `~' it expands to the invokers home
     directory as reflected in the value of the variable _✓h_✓o_✓m_✓e. When followed
     by a name consisting of letters, digits and `-' characters the shell
     searches for a user with that name and substitutes their home directory;
     thus `~ken' might expand to `/usr/ken' and `~ken/chmach' to
     `/usr/ken/chmach'.  If the character `~' is followed by a character other
     than a letter or `/' or appears not at the beginning of a word, it is
     left undisturbed.

     The metanotation `a{b,c,d}e' is a shorthand for `abe ace ade'.  Left to
     right order is preserved, with results of matches being sorted separately
     at a low level to preserve this order.  This construct may be nested.
     Thus `~source/s1/{oldls,ls}.c' expands to `/usr/source/s1/oldls.c
     /usr/source/s1/ls.c' whether or not these files exist without any chance
     of error if the home directory for `source' is `/usr/source'.  Similarly
     `../{memo,*box}' might expand to `../memo ../box ../mbox'.  (Note that
     `memo' was not sorted with the results of matching `*box'.)  As a special
     case `{', `}' and `{}' are passed undisturbed.

   I✓In✓np✓pu✓ut✓t/✓/o✓ou✓ut✓tp✓pu✓ut✓t
     The standard input and standard output of a command may be redirected
     with the following syntax:

           < name  Open file _✓n_✓a_✓m_✓e (which is first variable, command and file-
                   name expanded) as the standard input.
           << word
                   Read the shell input up to a line which is identical to
                   _✓w_✓o_✓r_✓d. _✓W_✓o_✓r_✓d is not subjected to variable, filename or com-
                   mand substitution, and each input line is compared to _✓w_✓o_✓r_✓d
                   before any substitutions are done on this input line.  Un-
                   less a quoting `\', `"', `' or ``' appears in _✓w_✓o_✓r_✓d variable
                   and command substitution is performed on the intervening
                   lines, allowing `\' to quote `$', `\' and ``'.  Commands
                   which are substituted have all blanks, tabs, and newlines
                   preserved, except for the final newline which is dropped.
                   The resultant text is placed in an anonymous temporary file
                   which is given to the command as standard input.
           > name
           >! name
           >& name
           >&! name
                   The file _✓n_✓a_✓m_✓e is used as standard output.  If the file does
                   not exist then it is created; if the file exists, its is
                   truncated, its previous contents being lost.

                   If the variable _✓n_✓o_✓c_✓l_✓o_✓b_✓b_✓e_✓r is set, then the file must not
                   exist or be a character special file (e.g. a terminal or
                   `/dev/null') or an error results.  This helps prevent acci-
                   dental destruction of files.  In this case the `!' forms
                   can be used and suppress this check.

                   The forms involving `&' route the diagnostic output into
                   the specified file as well as the standard output.  _✓N_✓a_✓m_✓e is
                   expanded in the same way as `<' input filenames are.
           >> name
           >>& name
           >>! name
           >>&! name
                   Uses file _✓n_✓a_✓m_✓e as standard output like `>' but places out-
                   put at the end of the file.  If the variable _✓n_✓o_✓c_✓l_✓o_✓b_✓b_✓e_✓r is
                   set, then it is an error for the file not to exist unless
                   one of the `!' forms is given.  Otherwise similar to `>'.

     A command receives the environment in which the shell was invoked as mod-
     ified by the input-output parameters and the presence of the command in a
     pipeline.  Thus, unlike some previous shells, commands run from a file of
     shell commands have no access to the text of the commands by default;
     rather they receive the original standard input of the shell.  The `<<'
     mechanism should be used to present inline data.  This permits shell com-
     mand scripts to function as components of pipelines and allows the shell
     to block read its input.  Note that the default standard input for a com-
     mand run detached is _✓n_✓o_✓t modified to be the empty file _✓/_✓d_✓e_✓v_✓/_✓n_✓u_✓l_✓l; rather
     the standard input remains as the original standard input of the shell.
     If this is a terminal and if the process attempts to read from the termi-
     nal, then the process will block and the user will be notified (see _✓J_✓o_✓b_✓s
     above).

     Diagnostic output may be directed through a pipe with the standard out-
     put.  Simply use the form `|&' rather than just `|'.

   E✓Ex✓xp✓pr✓re✓es✓ss✓si✓io✓on✓ns✓s
     A number of the builtin commands (to be described subsequently) take ex-
     pressions, in which the operators are similar to those of C, with the
     same precedence.  These expressions appear in the @✓@,✓, _✓e_✓x_✓i_✓t, _✓i_✓f, and _✓w_✓h_✓i_✓l_✓e
     commands.  The following operators are available:

           ||  &&  | *(ua  &  ==  !=  =~  !~  <=  >= <  > <<  >>  +  -  *  /
           %  !  ~  (  )

     Here the precedence increases to the right, `==' `!=' `=~' and `!~', `<='
     `>=' `<' and `>', `<<' and `>>', `+' and `-', `*' `/' and `%' being, in
     groups, at the same level.  The `==' `!=' `=~' and `!~' operators compare
     their arguments as strings; all others operate on numbers.  The operators
     `=~' and `!~' are like `!=' and `==' except that the right hand side is a
     _✓p_✓a_✓t_✓t_✓e_✓r_✓n (containing, e.g. `*'s, `?'s and instances of `[...]'  against
     which the left hand operand is matched.  This reduces the need for use of
     the _✓s_✓w_✓i_✓t_✓c_✓h statement in shell scripts when all that is really needed is
     pattern matching.

     Strings which begin with `0' are considered octal numbers.  Null or miss-
     ing arguments are considered `0'.  The result of all expressions are
     strings, which represent decimal numbers.  It is important to note that
     no two components of an expression can appear in the same word; except
     when adjacent to components of expressions which are syntactically sig-
     nificant to the parser (`&' `|' `<' `>' `(' `)') they should be surround-
     ed by spaces.

     Also available in expressions as primitive operands are command execu-
     tions enclosed in `{' and `}' and file enquiries of the form -✓-l✓l _✓n_✓a_✓m_✓e
     where l✓l is one of:

           r    read access w    write access x    execute access e    exis-
           tence o    ownership z    zero size f    plain file d    directory

     The specified name is command and filename expanded and then tested to
     see if it has the specified relationship to the real user.  If the file
     does not exist or is inaccessible then all enquiries return false, i.e.
     `0'.  Command executions succeed, returning true, i.e. `1', if the com-
     mand exits with status 0, otherwise they fail, returning false, i.e. `0'.
     If more detailed status information is required then the command should
     be executed outside of an expression and the variable _✓s_✓t_✓a_✓t_✓u_✓s examined.

   C✓Co✓on✓nt✓tr✓ro✓ol✓l f✓fl✓lo✓ow✓w
     The shell contains a number of commands which can be used to regulate the
     flow of control in command files (shell scripts) and (in limited but use-
     ful ways) from terminal input.  These commands all operate by forcing the
     shell to reread or skip in its input and, due to the implementation, re-
     strict the placement of some of the commands.

     The f✓fo✓or✓re✓ea✓ac✓ch✓h, s✓sw✓wi✓it✓tc✓ch✓h, and w✓wh✓hi✓il✓le✓e statements, as well as the i✓if✓f-✓-t✓th✓he✓en✓n-✓-e✓el✓ls✓se✓e
     form of the i✓if✓f statement require that the major keywords appear in a sin-
     gle simple command on an input line as shown below.

     If the shell's input is not seekable, the shell buffers up input whenever
     a loop is being read and performs seeks in this internal buffer to accom-
     plish the rereading implied by the loop.  (To the extent that this al-
     lows, backward goto's will succeed on non-seekable inputs.)

   B✓Bu✓ui✓il✓lt✓ti✓in✓n c✓co✓om✓mm✓ma✓an✓nd✓ds✓s
     Builtin commands are executed within the shell.  If a builtin command oc-
     curs as any component of a pipeline except the last then it is executed
     in a subshell.

           a✓al✓li✓ia✓as✓s
           a✓al✓li✓ia✓as✓s _✓n_✓a_✓m_✓e
           a✓al✓li✓ia✓as✓s _✓n_✓a_✓m_✓e _✓w_✓o_✓r_✓d_✓l_✓i_✓s_✓t
                   The first form prints all aliases.  The second form prints
                   the alias for name.  The final form assigns the specified
                   _✓w_✓o_✓r_✓d_✓l_✓i_✓s_✓t as the alias of _✓n_✓a_✓m_✓e; _✓w_✓o_✓r_✓d_✓l_✓i_✓s_✓t is command and
                   filename substituted.  _✓N_✓a_✓m_✓e is not allowed to be _✓a_✓l_✓i_✓a_✓s or
                   _✓u_✓n_✓a_✓l_✓i_✓a_✓s.

           a✓al✓ll✓lo✓oc✓c   Shows the amount of dynamic memory acquired, broken down
                   into used and free memory.  With an argument shows the num-
                   ber of free and used blocks in each size category.  The
                   categories start at size 8 and double at each step.  This
                   command's output may vary across system types, since sys-
                   tems other than the VAX may use a different memory alloca-
                   tor.

           b✓bg✓g
           b✓bg✓g %✓%_✓j_✓o_✓b _✓._✓._✓.
                   Puts the current or specified jobs into the background,
                   continuing them if they were stopped.



           b✓br✓re✓ea✓ak✓k   Causes execution to resume after the e✓en✓nd✓d of the nearest en-
                   closing f✓fo✓or✓re✓ea✓ac✓ch✓h or w✓wh✓hi✓il✓le✓e. The remaining commands on the
                   current line are executed.  Multi-level breaks are thus
                   possible by writing them all on one line.

           b✓br✓re✓ea✓ak✓ks✓sw✓w
                   Causes a break from a s✓sw✓wi✓it✓tc✓ch✓h, resuming after the e✓en✓nd✓ds✓sw✓w.

           c✓ca✓as✓se✓e _✓l_✓a_✓b_✓e_✓l:
                   A label in a s✓sw✓wi✓it✓tc✓ch✓h statement as discussed below.

           c✓cd✓d
           c✓cd✓d _✓n_✓a_✓m_✓e
           c✓ch✓hd✓di✓ir✓r
           c✓ch✓hd✓di✓ir✓r _✓n_✓a_✓m_✓e
                   Change the shell's working directory to directory _✓n_✓a_✓m_✓e. If
                   no argument is given then change to the home directory of
                   the user.  If _✓n_✓a_✓m_✓e is not found as a subdirectory of the
                   current directory (and does not begin with `/', `./' or
                   `../'), then each component of the variable c✓cd✓dp✓pa✓at✓th✓h is
                   checked to see if it has a subdirectory _✓n_✓a_✓m_✓e. Finally, if
                   all else fails but _✓n_✓a_✓m_✓e is a shell variable whose value be-
                   gins with `/', then this is tried to see if it is a direc-
                   tory.

           c✓co✓on✓nt✓ti✓in✓nu✓ue✓e
                   Continue execution of the nearest enclosing w✓wh✓hi✓il✓le✓e or
                   f✓fo✓or✓re✓ea✓ac✓ch✓h. The rest of the commands on the current line are
                   executed.

           d✓de✓ef✓fa✓au✓ul✓lt✓t:
                   Labels the default case in a s✓sw✓wi✓it✓tc✓ch✓h statement.  The default
                   should come after all c✓ca✓as✓se✓e labels.

           d✓di✓ir✓rs✓s    Prints the directory stack; the top of the stack is at the
                   left, the first directory in the stack being the current
                   directory.

           e✓ec✓ch✓ho✓o _✓w_✓o_✓r_✓d_✓l_✓i_✓s_✓t
           e✓ec✓ch✓ho✓o -✓-n✓n _✓w_✓o_✓r_✓d_✓l_✓i_✓s_✓t
                   The specified words are written to the shells standard out-
                   put, separated by spaces, and terminated with a newline un-
                   less the -✓-n✓n option is specified.

           e✓el✓ls✓se✓e
           e✓en✓nd✓d
           e✓en✓nd✓di✓if✓f
           e✓en✓nd✓ds✓sw✓w   See the description of the f✓fo✓or✓re✓ea✓ac✓ch✓h, i✓if✓f, s✓sw✓wi✓it✓tc✓ch✓h, and w✓wh✓hi✓il✓le✓e
                   statements below.

           e✓ev✓va✓al✓l _✓a_✓r_✓g _✓._✓._✓.
                   (As in sh(1).)  The arguments are read as input to the
                   shell and the resulting command(s) executed in the context
                   of the current shell.  This is usually used to execute com-
                   mands generated as the result of command or variable sub-
                   stitution, since parsing occurs before these substitutions.
                   See tset(1) for an example of using e✓ev✓va✓al✓l.

           e✓ex✓xe✓ec✓c _✓c_✓o_✓m_✓m_✓a_✓n_✓d
                   The specified command is executed in place of the current
                   shell.

           e✓ex✓xi✓it✓t
           e✓ex✓xi✓it✓t _✓(_✓e_✓x_✓p_✓r)
                   The shell exits either with the value of the s✓st✓ta✓at✓tu✓us✓s vari-
                   able (first form) or with the value of the specified e✓ex✓xp✓pr✓r
                   (second form).

           f✓fg✓g
           f✓fg✓g %✓% _✓j_✓o_✓b _✓._✓._✓.
                   Brings the current or specified jobs into the foreground,
                   continuing them if they were stopped.

           f✓fo✓or✓re✓ea✓ac✓ch✓h _✓n_✓a_✓m_✓e _✓(_✓w_✓o_✓r_✓d_✓l_✓i_✓s_✓t_✓)
           ...
           e✓en✓nd✓d     The variable n✓na✓am✓me✓e is successively set to each member of
                   w✓wo✓or✓rd✓dl✓li✓is✓st✓t and the sequence of commands between this command
                   and the matching e✓en✓nd✓d are executed.  (Both f✓fo✓or✓re✓ea✓ac✓ch✓h and e✓en✓nd✓d
                   must appear alone on separate lines.)  The builtin command
                   c✓co✓on✓nt✓ti✓in✓nu✓ue✓e may be used to continue the loop prematurely and
                   the builtin command b✓br✓re✓ea✓ak✓k to terminate it prematurely.
                   When this command is read from the terminal, the loop is
                   read up once prompting with `?' before any statements in
                   the loop are executed.  If you make a mistake typing in a
                   loop at the terminal you can rub it out.

           g✓gl✓lo✓ob✓b _✓w_✓o_✓r_✓d_✓l_✓i_✓s_✓t
                   Like e✓ec✓ch✓ho✓o but no `\' escapes are recognized and words are
                   delimited by null characters in the output.  Useful for
                   programs which wish to use the shell to filename expand a
                   list of words.

           g✓go✓ot✓to✓o _✓w_✓o_✓r_✓d
                   The specified w✓wo✓or✓rd✓d is filename and command expanded to
                   yield a string of the form `label'.  The shell rewinds its
                   input as much as possible and searches for a line of the
                   form `label:' possibly preceded by blanks or tabs.  Execu-
                   tion continues after the specified line.

           h✓ha✓as✓sh✓hs✓st✓ta✓at✓t
                   Print a statistics line indicating how effective the inter-
                   nal hash table has been at locating commands (and avoiding
                   e✓ex✓xe✓ec✓c's). An e✓ex✓xe✓ec✓c is attempted for each component of the
                   _✓p_✓a_✓t_✓h where the hash function indicates a possible hit, and
                   in each component which does not begin with a `/'.

           h✓hi✓is✓st✓to✓or✓ry✓y
           h✓hi✓is✓st✓to✓or✓ry✓y _✓n
           h✓hi✓is✓st✓to✓or✓ry✓y -✓-r✓r _✓n
           h✓hi✓is✓st✓to✓or✓ry✓y -✓-h✓h _✓n
                   Displays the history event list; if _✓n is given only the _✓n
                   most recent events are printed.  The -✓-r✓r option reverses the
                   order of printout to be most recent first rather than old-
                   est first.  The -✓-h✓h option causes the history list to be
                   printed without leading numbers.  This is used to produce
                   files suitable for sourceing using the -h option to s✓so✓ou✓ur✓rc✓ce✓e.

           i✓if✓f (_✓e_✓x_✓p_✓r command)
                   If the specified expression evaluates true, then the single
                   _✓c_✓o_✓m_✓m_✓a_✓n_✓d with arguments is executed.  Variable substitution
                   on _✓c_✓o_✓m_✓m_✓a_✓n_✓d happens early, at the same time it does for the
                   rest of the i✓if✓f command.  _✓C_✓o_✓m_✓m_✓a_✓n_✓d must be a simple command,
                   not a pipeline, a command list, or a parenthesized command
                   list.  Input/output redirection occurs even if _✓e_✓x_✓p_✓r is
                   false, when command is n✓no✓ot✓t executed (this is a bug).

           i✓if✓f (_✓e_✓x_✓p_✓r) t✓th✓he✓en✓n
           ...
           e✓el✓ls✓se✓e i✓if✓f (_✓e_✓x_✓p_✓r_✓2) t✓th✓he✓en✓n
           ...


           e✓el✓ls✓se✓e
           ...
           e✓en✓nd✓di✓if✓f   If the specified _✓e_✓x_✓p_✓r is true then the commands to the
                   first e✓el✓ls✓se✓e are executed; otherwise if _✓e_✓x_✓p_✓r_✓2 is true then
                   the commands to the second e✓el✓ls✓se✓e are executed, etc.  Any
                   number of e✓el✓ls✓se✓e-✓-i✓if✓f pairs are possible; only one e✓en✓nd✓di✓if✓f is
                   needed.  The e✓el✓ls✓se✓e part is likewise optional.  (The words
                   e✓el✓ls✓se✓e and e✓en✓nd✓di✓if✓f must appear at the beginning of input lines;
                   the i✓if✓f must appear alone on its input line or after an
                   e✓el✓ls✓se✓e.)

           j✓jo✓ob✓bs✓s
           j✓jo✓ob✓bs✓s -✓-l✓l
                   Lists the active jobs; given the -✓-l✓l options lists process
                   id's in addition to the normal information.

           k✓ki✓il✓ll✓l %✓% _✓j_✓o_✓b
           k✓ki✓il✓ll✓l _✓p_✓i_✓d
           k✓ki✓il✓ll✓l -✓-s✓si✓ig✓g _✓p_✓i_✓d _✓._✓._✓.
           k✓ki✓il✓ll✓l -✓-l✓l
                   Sends either the TERM (terminate) signal or the specified
                   signal to the specified jobs or processes.  Signals are ei-
                   ther given by number or by names (as given in
                   _✓/_✓u_✓s_✓r_✓/_✓i_✓n_✓c_✓l_✓u_✓d_✓e_✓/_✓s_✓i_✓g_✓n_✓a_✓l_✓._✓h_✓, stripped of the prefix ``SIG'').
                   The signal names are listed by ``kill -l''.  There is no
                   default, saying just `kill' does not send a signal to the
                   current job.  If the signal being sent is TERM (terminate)
                   or HUP (hangup), then the job or process will be sent a
                   CONT (continue) signal as well.

           l✓li✓im✓mi✓it✓t
           l✓li✓im✓mi✓it✓t _✓r_✓e_✓s_✓o_✓u_✓r_✓c_✓e
           l✓li✓im✓mi✓it✓t _✓r_✓e_✓s_✓o_✓u_✓r_✓c_✓e _✓m_✓a_✓x_✓i_✓m_✓u_✓m_✓-_✓u_✓s_✓e
           l✓li✓im✓mi✓it✓t -✓-h✓h
           l✓li✓im✓mi✓it✓t -✓-h✓h _✓r_✓e_✓s_✓o_✓u_✓r_✓c_✓e
           l✓li✓im✓mi✓it✓t -✓-h✓h _✓r_✓e_✓s_✓o_✓u_✓r_✓c_✓e _✓m_✓a_✓x_✓i_✓m_✓u_✓m_✓-_✓u_✓s_✓e
                   Limits the consumption by the current process and each pro-
                   cess it creates to not individually exceed _✓m_✓a_✓x_✓i_✓m_✓u_✓m_✓-_✓u_✓s_✓e on
                   the specified _✓r_✓e_✓s_✓o_✓u_✓r_✓c_✓e. If no _✓m_✓a_✓x_✓i_✓m_✓u_✓m_✓-_✓u_✓s_✓e is given, then
                   the current limit is printed; if no _✓r_✓e_✓s_✓o_✓u_✓r_✓c_✓e is given, then
                   all limitations are given.  If the -✓-h✓h flag is given, the
                   hard limits are used instead of the current limits.  The
                   hard limits impose a ceiling on the values of the current
                   limits.  Only the super-user may raise the hard limits, but
                   a user may lower or raise the current limits within the le-
                   gal range.

                   Resources controllable currently include _✓c_✓p_✓u_✓t_✓i_✓m_✓e (the maxi-
                   mum number of cpu-seconds to be used by each process),
                   _✓f_✓i_✓l_✓e_✓s_✓i_✓z_✓e (the largest single file which can be created),
                   _✓d_✓a_✓t_✓a_✓s_✓i_✓z_✓e (the maximum growth of the data+stack region via
                   sbrk(2) beyond the end of the program text), _✓s_✓t_✓a_✓c_✓k_✓s_✓i_✓z_✓e (the
                   maximum size of the automatically-extended stack region),
                   and _✓c_✓o_✓r_✓e_✓d_✓u_✓m_✓p_✓s_✓i_✓z_✓e (the size of the largest core dump that
                   will be created).

                   The _✓m_✓a_✓x_✓i_✓m_✓u_✓m_✓-_✓u_✓s_✓e may be given as a (floating point or inte-
                   ger) number followed by a scale factor.  For all limits
                   other than _✓c_✓p_✓u_✓t_✓i_✓m_✓e the default scale is `k' or `kilobytes'
                   (1024 bytes); a scale factor of `m' or `megabytes' may also
                   be used.  For _✓c_✓p_✓u_✓t_✓i_✓m_✓e the default scaling is `seconds',
                   while `m' for minutes or `h' for hours, or a time of the
                   form `mm:ss' giving minutes and seconds may be used.

                   For both _✓r_✓e_✓s_✓o_✓u_✓r_✓c_✓e names and scale factors, unambiguous pre-
                   fixes of the names suffice.

           l✓lo✓og✓gi✓in✓n   Terminate a login shell, replacing it with an instance of
                   _✓/_✓b_✓i_✓n_✓/_✓l_✓o_✓g_✓i_✓n_✓. This is one way to log off, included for com-
                   patibility with sh(1).

           l✓lo✓og✓go✓ou✓ut✓t  Terminate a login shell.  Especially useful if i✓ig✓gn✓no✓or✓re✓ee✓eo✓of✓f is
                   set.

           n✓ni✓ic✓ce✓e
           n✓ni✓ic✓ce✓e _✓+_✓n_✓u_✓m_✓b_✓e_✓r
           n✓ni✓ic✓ce✓e _✓c_✓o_✓m_✓m_✓a_✓n_✓d
           n✓ni✓ic✓ce✓e _✓+_✓n_✓u_✓m_✓b_✓e_✓r _✓c_✓o_✓m_✓m_✓a_✓n_✓d
                   The first form sets the scheduling priority for this shell
                   to 4.  The second form sets the priority to the given
                   _✓n_✓u_✓m_✓b_✓e_✓r. The final two forms run command at priority 4 and
                   _✓n_✓u_✓m_✓b_✓e_✓r respectively.  The greater the number, the less cpu
                   the process will get.  The super-user may specify negative
                   priority by using `nice -number ...'.  Command is always
                   executed in a sub-shell, and the restrictions placed on
                   commands in simple i✓if✓f statements apply.

           n✓no✓oh✓hu✓up✓p
           n✓no✓oh✓hu✓up✓p _✓c_✓o_✓m_✓m_✓a_✓n_✓d
                   The first form can be used in shell scripts to cause
                   hangups to be ignored for the remainder of the script.  The
                   second form causes the specified command to be run with
                   hangups ignored.  All processes detached with `&' are ef-
                   fectively n✓no✓oh✓hu✓up✓p'ed.

           n✓no✓ot✓ti✓if✓fy✓y
           n✓no✓ot✓ti✓if✓fy✓y %✓% _✓j_✓o_✓b _✓._✓._✓.
                   Causes the shell to notify the user asynchronously when the
                   status of the current or specified jobs changes; normally
                   notification is presented before a prompt.  This is auto-
                   matic if the shell variable n✓no✓ot✓ti✓if✓fy✓y is set.

           o✓on✓ni✓in✓nt✓tr✓r
           o✓on✓ni✓in✓nt✓tr✓r -✓-
           o✓on✓ni✓in✓nt✓tr✓r _✓l_✓a_✓b_✓e_✓l
                   Control the action of the shell on interrupts.  The first
                   form restores the default action of the shell on interrupts
                   which is to terminate shell scripts or to return to the
                   terminal command input level.  The second form `onintr -'
                   causes all interrupts to be ignored.  The final form causes
                   the shell to execute a `goto label' when an interrupt is
                   received or a child process terminates because it was in-
                   terrupted.

                   In any case, if the shell is running detached and inter-
                   rupts are being ignored, all forms of o✓on✓ni✓in✓nt✓tr✓r have no mean-
                   ing and interrupts continue to be ignored by the shell and
                   all invoked commands.

           p✓po✓op✓pd✓d
           p✓po✓op✓pd✓d _✓+_✓n
                   Pops the directory stack, returning to the new top directo-
                   ry.  With an argument `+ _✓n' discards the _✓n'th entry in the
                   stack.  The elements of the directory stack are numbered
                   from 0 starting at the top.

           p✓pu✓us✓sh✓hd✓d
           p✓pu✓us✓sh✓hd✓d _✓n_✓a_✓m_✓e
           p✓pu✓us✓sh✓hd✓d _✓n
                   With no arguments, p✓pu✓us✓sh✓hd✓d exchanges the top two elements of
                   the directory stack.  Given a _✓n_✓a_✓m_✓e argument, p✓pu✓us✓sh✓hd✓d changes
                   to the new directory (ala c✓cd✓d) and pushes the old current
                   working directory (as in c✓cs✓sw✓w) onto the directory stack.
                   With a numeric argument, rotates the _✓n'th argument of the
                   directory stack around to be the top element and changes to
                   it.  The members of the directory stack are numbered from
                   the top starting at 0.

           r✓re✓eh✓ha✓as✓sh✓h  Causes the internal hash table of the contents of the di-
                   rectories in the p✓pa✓at✓th✓h variable to be recomputed.  This is
                   needed if new commands are added to directories in the p✓pa✓at✓th✓h
                   while you are logged in.  This should only be necessary if
                   you add commands to one of your own directories, or if a
                   systems programmer changes the contents of one of the sys-
                   tem directories.

           r✓re✓ep✓pe✓ea✓at✓t _✓c_✓o_✓u_✓n_✓t _✓c_✓o_✓m_✓m_✓a_✓n_✓d
                   The specified _✓c_✓o_✓m_✓m_✓a_✓n_✓d which is subject to the same restric-
                   tions as the _✓c_✓o_✓m_✓m_✓a_✓n_✓d in the one line i✓if✓f statement above, is
                   executed _✓c_✓o_✓u_✓n_✓t times.  I/O redirections occur exactly once,
                   even if _✓c_✓o_✓u_✓n_✓t is 0.

           s✓se✓et✓t
           s✓se✓et✓t _✓n_✓a_✓m_✓e
           s✓se✓et✓t _✓n_✓a_✓m_✓e=word
           s✓se✓et✓t _✓n_✓a_✓m_✓e_✓[_✓i_✓n_✓d_✓e_✓x_✓]=word
           s✓se✓et✓t _✓n_✓a_✓m_✓e=(wordlist)
                   The first form of the command shows the value of all shell
                   variables.  Variables which have other than a single word
                   as value print as a parenthesized word list.  The second
                   form sets n✓na✓am✓me✓e to the null string.  The third form sets
                   n✓na✓am✓me✓e to the single w✓wo✓or✓rd✓d. The fourth form sets the _✓i_✓n_✓d_✓e_✓x'th
                   component of name to word; this component must already ex-
                   ist.  The final form sets _✓n_✓a_✓m_✓e to the list of words in
                   _✓w_✓o_✓r_✓d_✓l_✓i_✓s_✓t. In all cases the value is command and filename
                   expanded.

                   These arguments may be repeated to set multiple values in a
                   single set command.  Note however, that variable expansion
                   happens for all arguments before any setting occurs.

           s✓se✓et✓te✓en✓nv✓v
           s✓se✓et✓te✓en✓nv✓v _✓n_✓a_✓m_✓e _✓v_✓a_✓l_✓u_✓e
           s✓se✓et✓te✓en✓nv✓v _✓n_✓a_✓m_✓e
                   The first form lists all current environment variables.
                   The last form sets the value of environment variable _✓n_✓a_✓m_✓e
                   to be _✓v_✓a_✓l_✓u_✓e, a single string.  The second form sets _✓n_✓a_✓m_✓e to
                   an empty string.  The most commonly used environment vari-
                   able USER, TERM, and PATH are automatically imported to and
                   exported from the c✓cs✓sh✓h variables _✓u_✓s_✓e_✓r, [_✓t_✓e_✓r_✓m], and _✓p_✓a_✓t_✓h;
                   there is no need to use s✓se✓et✓te✓en✓nv✓v for these.

           s✓sh✓hi✓if✓ft✓t
           s✓sh✓hi✓if✓ft✓t _✓v_✓a_✓r_✓i_✓a_✓b_✓l_✓e
                   The members of a✓ar✓rg✓gv✓v are shifted to the left, discarding
                   a✓ar✓rg✓gv✓v [1]. It is an error for a✓ar✓rg✓gv✓v not to be set or to have
                   less than one word as value.  The second form performs the
                   same function on the specified variable.

           s✓so✓ou✓ur✓rc✓ce✓e _✓n_✓a_✓m_✓e
           s✓so✓ou✓ur✓rc✓ce✓e -✓-h✓h _✓n_✓a_✓m_✓e
                   The shell reads commands from n✓na✓am✓me✓e. S✓So✓ou✓ur✓rc✓ce✓e commands may be
                   nested; if they are nested too deeply the shell may run out
                   of file descriptors.  An error in a s✓so✓ou✓ur✓rc✓ce✓e at any level
                   terminates all nested s✓so✓ou✓ur✓rc✓ce✓e commands.  Normally input dur-
                   ing s✓so✓ou✓ur✓rc✓ce✓e commands is not placed on the history list; the
                   -h option causes the commands to be placed in the history
                   list without being executed.

           s✓st✓to✓op✓p
           s✓st✓to✓op✓p %✓%_✓j_✓o_✓b _✓._✓._✓.
                   Stops the current or specified job which is executing in
                   the background.

           s✓su✓us✓sp✓pe✓en✓nd✓d
                   Causes the shell to stop in its tracks, much as if it had
                   been sent a stop signal with ^✓^Z✓Z. This is most often used to
                   stop shells started by su(1).

           s✓sw✓wi✓it✓tc✓ch✓h _✓(_✓s_✓t_✓r_✓i_✓n_✓g_✓)
           c✓ca✓as✓se✓e _✓s_✓t_✓r_✓1:
               ...
               b✓br✓re✓ea✓ak✓ks✓sw✓w
               ...
           d✓de✓ef✓fa✓au✓ul✓lt✓t:
               ...
               b✓br✓re✓ea✓ak✓ks✓sw✓w
           e✓en✓nd✓ds✓sw✓w   Each case label is successively matched, against the speci-
                   fied _✓s_✓t_✓r_✓i_✓n_✓g which is first command and filename expanded.
                   The file metacharacters `*', `?' and `[...]'  may be used
                   in the case labels, which are variable expanded.  If none
                   of the labels match before a `default' label is found, then
                   the execution begins after the default label.  Each case
                   label and the default label must appear at the beginning of
                   a line.  The command b✓br✓re✓ea✓ak✓ks✓sw✓w causes execution to continue
                   after the e✓en✓nd✓ds✓sw✓w. Otherwise control may fall through case
                   labels and default labels as in C.  If no label matches and
                   there is no default, execution continues after the e✓en✓nd✓ds✓sw✓w.

           t✓ti✓im✓me✓e
           t✓ti✓im✓me✓e _✓c_✓o_✓m_✓m_✓a_✓n_✓d
                   With no argument, a summary of time used by this shell and
                   its children is printed.  If arguments are given the speci-
                   fied simple command is timed and a time summary as de-
                   scribed under the t✓ti✓im✓me✓e variable is printed.  If necessary,
                   an extra shell is created to print the time statistic when
                   the command completes.

           u✓um✓ma✓as✓sk✓k
           u✓um✓ma✓as✓sk✓k _✓v_✓a_✓l_✓u_✓e
                   The file creation mask is displayed (first form) or set to
                   the specified value (second form).  The mask is given in
                   octal.  Common values for the mask are 002 giving all ac-
                   cess to the group and read and execute access to others or
                   022 giving all access except no write access for users in
                   the group or others.

           u✓un✓na✓al✓li✓ia✓as✓s _✓p_✓a_✓t_✓t_✓e_✓r_✓n
                   All aliases whose names match the specified pattern are
                   discarded.  Thus all aliases are removed by `unalias *'.
                   It is not an error for nothing to be u✓un✓na✓al✓li✓ia✓as✓se✓ed✓d.

           u✓un✓nh✓ha✓as✓sh✓h  Use of the internal hash table to speed location of execut-
                   ed programs is disabled.

           u✓un✓nl✓li✓im✓mi✓it✓t
           u✓un✓nl✓li✓im✓mi✓it✓t _✓r_✓e_✓s_✓o_✓u_✓r_✓c_✓e
           u✓un✓nl✓li✓im✓mi✓it✓t -✓-h✓h
           u✓un✓nl✓li✓im✓mi✓it✓t -✓-h✓h _✓r_✓e_✓s_✓o_✓u_✓r_✓c_✓e
                   Removes the limitation on _✓r_✓e_✓s_✓o_✓u_✓r_✓c_✓e. If no _✓r_✓e_✓s_✓o_✓u_✓r_✓c_✓e is spec-
                   ified, then all _✓r_✓e_✓s_✓o_✓u_✓r_✓c_✓e limitations are removed.  If -✓-h✓h is
                   given, the corresponding hard limits are removed.  Only the
                   super-user may do this.


           u✓un✓ns✓se✓et✓t _✓p_✓a_✓t_✓t_✓e_✓r_✓n
                   All variables whose names match the specified pattern are
                   removed.  Thus all variables are removed by `unset *'; this
                   has noticeably distasteful side-effects.  It is not an er-
                   ror for nothing to be u✓un✓ns✓se✓et✓t.

           u✓un✓ns✓se✓et✓te✓en✓nv✓v _✓p_✓a_✓t_✓t_✓e_✓r_✓n
                   Removes all variables whose name match the specified pat-
                   tern from the environment.  See also the s✓se✓et✓te✓en✓nv✓v command
                   above and printenv(1).

           w✓wa✓ai✓it✓t    All background jobs are waited for.  It the shell is inter-
                   active, then an interrupt can disrupt the wait, at which
                   time the shell prints names and job numbers of all jobs
                   known to be outstanding.

           w✓wh✓hi✓il✓le✓e _✓(_✓e_✓x_✓p_✓r_✓)
           ...
           e✓en✓nd✓d     While the specified expression evaluates non-zero, the com-
                   mands between the w✓wh✓hi✓il✓le✓e and the matching end are evaluated.
                   B✓Br✓re✓ea✓ak✓k and c✓co✓on✓nt✓ti✓in✓nu✓ue✓e may be used to terminate or continue the
                   loop prematurely.  (The w✓wh✓hi✓il✓le✓e and e✓en✓nd✓d must appear alone on
                   their input lines.)  Prompting occurs here the first time
                   through the loop as for the f✓fo✓or✓re✓ea✓ac✓ch✓h statement if the input
                   is a terminal.

           %✓% _✓j_✓o_✓b   Brings the specified job into the foreground.

           %✓% _✓j_✓o_✓b &✓&
                   Continues the specified job in the background.

           @✓@
           @✓@_✓n_✓a_✓m_✓e= expr
           @✓@_✓n_✓a_✓m_✓e_✓[_✓i_✓n_✓d_✓e_✓x_✓]= expr
                   The first form prints the values of all the shell vari-
                   ables.  The second form sets the specified _✓n_✓a_✓m_✓e to the val-
                   ue of _✓e_✓x_✓p_✓r. If the expression contains `<', `>', `&' or `'
                   then at least this part of the expression must be placed
                   within `(' `)'.  The third form assigns the value of _✓e_✓x_✓p_✓r
                   to the _✓i_✓n_✓d_✓e_✓x'th argument of _✓n_✓a_✓m_✓e. Both _✓n_✓a_✓m_✓e and its
                   _✓i_✓n_✓d_✓e_✓x'th component must already exist.

     The operators `*=', `+=', etc are available as in C.  The space separat-
     ing the name from the assignment operator is optional.  Spaces are, how-
     ever, mandatory in separating components of _✓e_✓x_✓p_✓r which would otherwise be
     single words.

     Special postfix `++' and `--' operators increment and decrement _✓n_✓a_✓m_✓e re-
     spectively, i.e. `@  i++'.

   P✓Pr✓re✓e-✓-d✓de✓ef✓fi✓in✓ne✓ed✓d a✓an✓nd✓d e✓en✓nv✓vi✓ir✓ro✓on✓nm✓me✓en✓nt✓t v✓va✓ar✓ri✓ia✓ab✓bl✓le✓es✓s
     The following variables have special meaning to the shell.  Of these,
     _✓a_✓r_✓g_✓v, _✓c_✓w_✓d_✓, _✓h_✓o_✓m_✓e, _✓p_✓a_✓t_✓h_✓, _✓p_✓r_✓o_✓m_✓p_✓t, _✓s_✓h_✓e_✓l_✓l and _✓s_✓t_✓a_✓t_✓u_✓s are always set by the
     shell.  Except for _✓c_✓w_✓d and _✓s_✓t_✓a_✓t_✓u_✓s this setting occurs only at initializa-
     tion; these variables will not then be modified unless this is done ex-
     plicitly by the user.

     This shell copies the environment variable USER into the variable _✓u_✓s_✓e_✓r,
     TERM into _✓t_✓e_✓r_✓m, and HOME into _✓h_✓o_✓m_✓e, and copies these back into the envi-
     ronment whenever the normal shell variables are reset.  The environment
     variable PATH is likewise handled; it is not necessary to worry about its
     setting other than in the file _✓._✓c_✓s_✓h_✓r_✓c as inferior c✓cs✓sh✓h processes will im-
     port the definition of _✓p_✓a_✓t_✓h from the environment, and re-export it if you


     then change it.

     a✓ar✓rg✓gv✓v       Set to the arguments to the shell, it is from this variable
                that positional parameters are substituted, i.e. `$1' is re-
                placed by `$argv[1]', etc.

     c✓cd✓dp✓pa✓at✓th✓h     Gives a list of alternate directories searched to find subdi-
                rectories in _✓c_✓h_✓d_✓i_✓r commands.

     c✓cw✓wd✓d        The full pathname of the current directory.

     e✓ec✓ch✓ho✓o       Set when the -✓-x✓x command line option is given.  Causes each
                command and its arguments to be echoed just before it is exe-
                cuted.  For non-builtin commands all expansions occur before
                echoing.  Builtin commands are echoed before command and file-
                name substitution, since these substitutions are then done se-
                lectively.

     f✓fi✓il✓le✓ec✓c      Enable file name completion.

     h✓hi✓is✓st✓tc✓ch✓ha✓ar✓rs✓s  Can be given a string value to change the characters used in
                history substitution.  The first character of its value is
                used as the history substitution character, replacing the de-
                fault character `!'.  The second character of its value re-
                places the character `|✓^' in quick substitutions.

     h✓hi✓is✓st✓to✓or✓ry✓y    Can be given a numeric value to control the size of the histo-
                ry list.  Any command which has been referenced in this many
                events will not be discarded.  Too large values of _✓h_✓i_✓s_✓t_✓o_✓r_✓y may
                run the shell out of memory.  The last executed command is al-
                ways saved on the history list.

     h✓ho✓om✓me✓e       The home directory of the invoker, initialized from the envi-
                ronment.  The filename expansion of `_✓~' refers to this vari-
                able.

     i✓ig✓gn✓no✓or✓re✓ee✓eo✓of✓f  If set the shell ignores end-of-file from input devices which
                are terminals.  This prevents shells from accidentally being
                killed by control-D's.

     m✓ma✓ai✓il✓l       The files where the shell checks for mail.  This is done after
                each command completion which will result in a prompt, if a
                specified interval has elapsed.  The shell says `You have new
                mail.'  if the file exists with an access time not greater
                than its modify time.

                If the first word of the value of _✓m_✓a_✓i_✓l is numeric it specifies
                a different mail checking interval, in seconds, than the de-
                fault, which is 10 minutes.

                If multiple mail files are specified, then the shell says `New
                mail in _✓n_✓a_✓m_✓e' when there is mail in the file _✓n_✓a_✓m_✓e.

     n✓no✓oc✓cl✓lo✓ob✓bb✓be✓er✓r  As described in the section on _✓I_✓n_✓p_✓u_✓t_✓/_✓o_✓u_✓t_✓p_✓u_✓t, restrictions are
                placed on output redirection to insure that files are not ac-
                cidentally destroyed, and that `>>' redirections refer to ex-
                isting files.

     n✓no✓og✓gl✓lo✓ob✓b     If set, filename expansion is inhibited.  This is most useful
                in shell scripts which are not dealing with filenames, or af-
                ter a list of filenames has been obtained and further expan-
                sions are not desirable.

     n✓no✓on✓no✓om✓ma✓at✓tc✓ch✓h  If set, it is not an error for a filename expansion to not
                match any existing files; rather the primitive pattern is re-
                turned.  It is still an error for the primitive pattern to be

                malformed, i.e.  `echo [' still gives an error.

     n✓no✓ot✓ti✓if✓fy✓y     If set, the shell notifies asynchronously of job completions.
                The default is to rather present job completions just before
                printing a prompt.

     p✓pa✓at✓th✓h       Each word of the path variable specifies a directory in which
                commands are to be sought for execution.  A null word speci-
                fies the current directory.  If there is no _✓p_✓a_✓t_✓h variable then
                only full path names will execute.  The usual search path is
                `.', `/bin' and `/usr/bin', but this may vary from system to
                system.  For the super-user the default search path is `/etc',
                `/bin' and `/usr/bin'.  A shell which is given neither the -✓-c✓c
                nor the -✓-t✓t option will normally hash the contents of the di-
                rectories in the _✓p_✓a_✓t_✓h variable after reading _✓._✓c_✓s_✓h_✓r_✓c, and each
                time the _✓p_✓a_✓t_✓h variable is reset.  If new commands are added to
                these directories while the shell is active, it may be neces-
                sary to do a r✓re✓eh✓ha✓as✓sh✓h or the commands may not be found.

     p✓pr✓ro✓om✓mp✓pt✓t     The string which is printed before each command is read from
                an interactive terminal input.  If a `!' appears in the string
                it will be replaced by the current event number unless a pre-
                ceding `\' is given.  Default is `% ', or `# ' for the super-
                user.

     s✓sa✓av✓ve✓eh✓hi✓is✓st✓t   Is given a numeric value to control the number of entries of
                the history list that are saved in ~/.history when the user
                logs out.  Any command which has been referenced in this many
                events will be saved.  During start up the shell sources
                ~/.history into the history list enabling history to be saved
                across logins.  Too large values of _✓s_✓a_✓v_✓e_✓h_✓i_✓s_✓t will slow down
                the shell during start up.

     s✓sh✓he✓el✓ll✓l      The file in which the shell resides.  This is used in forking
                shells to interpret files which have execute bits set, but
                which are not executable by the system.  (See the description
                of _✓N_✓o_✓n_✓-_✓b_✓u_✓i_✓l_✓t_✓i_✓n _✓C_✓o_✓m_✓m_✓a_✓n_✓d _✓E_✓x_✓e_✓c_✓u_✓t_✓i_✓o_✓n below.)  Initialized to the
                (system-dependent) home of the shell.

     s✓st✓ta✓at✓tu✓us✓s     The status returned by the last command.  If it terminated ab-
                normally, then 0200 is added to the status.  Builtin commands
                which fail return exit status `1', all other builtin commands
                set status `0'.

     t✓ti✓im✓me✓e       Controls automatic timing of commands.  If set, then any com-
                mand which takes more than this many cpu seconds will cause a
                line giving user, system, and real times and a utilization
                percentage which is the ratio of user plus system times to re-
                al time to be printed when it terminates.

     v✓ve✓er✓rb✓bo✓os✓se✓e    Set by the -✓-v✓v command line option, causes the words of each
                command to be printed after history substitution.

   N✓No✓on✓n-✓-b✓bu✓ui✓il✓lt✓ti✓in✓n c✓co✓om✓mm✓ma✓an✓nd✓d e✓ex✓xe✓ec✓cu✓ut✓ti✓io✓on✓n
     When a command to be executed is found to not be a builtin command the
     shell attempts to execute the command via execve(2).  Each word in the
     variable _✓p_✓a_✓t_✓h names a directory from which the shell will attempt to exe-
     cute the command.  If it is given neither a -✓-c✓c nor a -✓-t✓t option, the shell
     will hash the names in these directories into an internal table so that
     it will only try an e✓ex✓xe✓ec✓c in a directory if there is a possibility that
     the command resides there.  This greatly speeds command location when a
     large number of directories are present in the search path.  If this
     mechanism has been turned off (via u✓un✓nh✓ha✓as✓sh✓h), or if the shell was given a
     -✓-c✓c or -✓-t✓t argument, and in any case for each directory component of _✓p_✓a_✓t_✓h
     which does not begin with a `/', the shell concatenates with the given
     command name to form a path name of a file which it then attempts to exe-
     cute.

     Parenthesized commands are always executed in a subshell.  Thus

           (cd; pwd); pwd

     prints the _✓h_✓o_✓m_✓e directory; leaving you where you were (printing this af-
     ter the home directory), while

           cd; pwd

     leaves you in the _✓h_✓o_✓m_✓e directory.  Parenthesized commands are most often
     used to prevent c✓ch✓hd✓di✓ir✓r from affecting the current shell.

     If the file has execute permissions but is not an executable binary to
     the system, then it is assumed to be a file containing shell commands and
     a new shell is spawned to read it.

     If there is an a✓al✓li✓ia✓as✓s for s✓sh✓he✓el✓ll✓l then the words of the alias will be
     prepended to the argument list to form the shell command.  The first word
     of the a✓al✓li✓ia✓as✓s should be the full path name of the shell (e.g. `$shell').
     Note that this is a special, late occurring, case of a✓al✓li✓ia✓as✓s substitution,
     and only allows words to be prepended to the argument list without modi-
     fication.

   S✓Si✓ig✓gn✓na✓al✓l h✓ha✓an✓nd✓dl✓li✓in✓ng✓g
     The shell normally ignores _✓q_✓u_✓i_✓t signals.  Jobs running detached (either
     by &✓& or the b✓bg✓g or %✓%.✓..✓..✓. &✓& commands) are immune to signals generated from
     the keyboard, including hangups.  Other signals have the values which the
     shell inherited from its parent.  The shell's handling of interrupts and
     terminate signals in shell scripts can be controlled by o✓on✓ni✓in✓nt✓tr✓r. Login
     shells catch the _✓t_✓e_✓r_✓m_✓i_✓n_✓a_✓t_✓e signal; otherwise this signal is passed on to
     children from the state in the shell's parent.  In no case are interrupts
     allowed when a login shell is reading the file _✓._✓l_✓o_✓g_✓o_✓u_✓t.

A✓AU✓UT✓TH✓HO✓OR✓R
     William Joy.  Job control and directory stack features first implemented
     by J.E. Kulp of IIASA, Laxenburg, Austria, with different syntax than
     that used now.  File name completion code written by Ken Greer, HP Labs.
     Eight-bit implementation Christos S. Zoulas, Cornell University.

F✓FI✓IL✓LE✓ES✓S
     ~/.cshrc     Read at beginning of execution by each shell.
     ~/.login     Read by login shell, after `.cshrc' at login.
     ~/.logout    Read by login shell, at logout.
     /bin/sh      Standard shell, for shell scripts not starting with a `#'.
     /tmp/sh*     Temporary file for `<<'.
     /etc/passwd  Source of home directories for `~name'.

L✓LI✓IM✓MI✓IT✓TA✓AT✓TI✓IO✓ON✓NS✓S
     Word lengths - Words can be no longer than 1024 characters.  The system
     limits argument lists to 10240 characters.  The number of arguments to a
     command which involves filename expansion is limited to 1/6'th the number
     of characters allowed in an argument list.  Command substitutions may
     substitute no more characters than are allowed in an argument list.  To
     detect looping, the shell restricts the number of a✓al✓li✓ia✓as✓s substitutions on
     a single line to 20.

S✓SE✓EE✓E A✓AL✓LS✓SO✓O
     sh(1),  access(2),  execve(2),  fork(2),  killpg(2),  pipe(2),
     sigvec(2),  umask(2),  setrlimit(2),  wait(2),  tty(4),  a.out(5),
     environ(7),
     introduction to the C shell

H✓HI✓IS✓ST✓TO✓OR✓RY✓Y
     C✓Cs✓sh✓h appeared in 3BSD. It was a first implementation of a command language
     interpreter incorporating a history mechanism (see _✓H_✓i_✓s_✓t_✓o_✓r_✓y
     _✓S_✓u_✓b_✓s_✓t_✓i_✓t_✓u_✓t_✓i_✓o_✓n_✓s), job control facilities (see _✓J_✓o_✓b_✓s), interactive file name
     and user name completion (see _✓F_✓i_✓l_✓e _✓N_✓a_✓m_✓e _✓C_✓o_✓m_✓p_✓l_✓e_✓t_✓i_✓o_✓n), and a C-like syntax.
     There are now many shells which also have these mechanisms, plus a few
     more (and maybe some bugs too), which are available thru the usenet, or
     with BSD UNIX as contributed software like the ksh(korn shell).

B✓BU✓UG✓GS✓S
     When a command is restarted from a stop, the shell prints the directory
     it started in if this is different from the current directory; this can
     be misleading (i.e. wrong) as the job may have changed directories inter-
     nally.

     Shell builtin functions are not stoppable/restartable.  Command sequences
     of the form `a ; b ; c' are also not handled gracefully when stopping is
     attempted.  If you suspend `b', the shell will then immediately execute
     `c'.  This is especially noticeable if this expansion results from an
     _✓a_✓l_✓i_✓a_✓s. It suffices to place the sequence of commands in ()'s to force it
     to a subshell, i.e. `( a ; b ; c )'.

     Control over tty output after processes are started is primitive; perhaps
     this will inspire someone to work on a good virtual terminal interface.
     In a virtual terminal interface much more interesting things could be
     done with output control.

     Alias substitution is most often used to clumsily simulate shell proce-
     dures; shell procedures should be provided rather than aliases.

     Commands within loops, prompted for by `?', are not placed in the h✓hi✓is✓st✓to✓or✓ry✓y
     list.  Control structure should be parsed rather than being recognized as
     built-in commands.  This would allow control commands to be placed any-
     where, to be combined with `|', and to be used with `&' and `;' metasyn-
     tax.

     It should be possible to use the `:' modifiers on the output of command
     substitutions.  All and more than one `:' modifier should be allowed on
     `$' substitutions.

     The way the f✓fi✓il✓le✓ec✓c facility is implemented is ugly and expensive.

4th Berkeley Distribution        June 7, 1991                               22