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csh(1)

NAME

       tcsh - C shell with file name completion and command line editing

SYNOPSIS

       tcsh [-bcdefFimnqstvVxX] [-Dname[=value]] [arg ...]
       tcsh -l

DESCRIPTION

       tcsh  is  an enhanced but completely compatible version of the Berkeley
       UNIX C shell, csh(1).  It is a command language interpreter usable both
       as an interactive login shell and a shell script command processor.  It
       includes a command-line editor  (see  The  command-line	editor),  pro-
       grammable  word	completion (see Completion and listing), spelling cor-
       rection (see Spelling correction), a  history  mechanism  (see  History
       substitution),  job  control  (see  Jobs) and a C-like syntax.  The NEW
       FEATURES section describes major  enhancements  of  tcsh  over  csh(1).
       Throughout  this  manual,  features  of	tcsh  not found in most csh(1)
       implementations (specifically, the 4.4BSD csh) are labeled with	`(+)',
       and features which are present in csh(1) but not usually documented are
       labeled with `(u)'.

   Argument list processing
       If the first argument (argument 0) to the shell is `-'  then  it  is  a
       login shell.  A login shell can be also specified by invoking the shell
       with the -l flag as the only argument.

       The rest of the flag arguments are interpreted as follows:

       -b  Forces a ``break'' from  option  processing,  causing  any  further
	   shell arguments to be treated as non-option arguments.  The remain-
	   ing arguments will not be interpreted as shell options.   This  may
	   be used to pass options to a shell script without confusion or pos-
	   sible subterfuge.  The shell will not  run  a  set-user  ID	script
	   without this option.

       -c  Commands  are  read	from  the  following  argument	(which must be
	   present, and must be a single  argument),  stored  in  the  command
	   shell  variable  for  reference, and executed.  Any remaining argu-
	   ments are placed in the argv shell variable.

       -d  The shell loads the directory stack from  ~/.cshdirs  as  described
	   under Startup and shutdown, whether or not it is a login shell. (+)

       -Dname[=value]
	   Sets the environment variable name to value. (Domain/OS only) (+)

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

       -f  The shell ignores ~/.tcshrc, and thus starts faster.

       -F  The	shell  uses  fork(2)  instead  of vfork(2) to spawn processes.
	   (Convex/OS only) (+)

       -i  The shell is interactive and prompts for its top-level input,  even

       -n  The shell parses commands but does not execute them.  This aids  in
	   debugging shell scripts.

       -q  The shell accepts SIGQUIT (see Signal handling) and behaves when it
	   is used under a debugger.  Job control is disabled. (u)

       -s  Command input is taken from the standard input.

       -t  The shell reads and executes a single line of input.  A `\' may  be
	   used  to  escape  the  newline at the end of this line and continue
	   onto another line.

       -v  Sets the verbose shell variable, so that command  input  is	echoed
	   after history substitution.

       -x  Sets  the  echo shell variable, so that commands are echoed immedi-
	   ately before execution.

       -V  Sets the verbose shell variable even before executing ~/.tcshrc.

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

       After processing of flag arguments, if arguments remain but none of the
       -c,  -i,  -s,  or -t options were given, the first argument is taken as
       the name of a file of commands, or ``script'',  to  be  executed.   The
       shell opens this file and saves its name for possible resubstitution by
       `$0'.  Because many systems use either the standard version 6  or  ver-
       sion  7	shells whose shell scripts are not compatible with this shell,
       the shell uses such a `standard' shell to execute a script whose  first
       character is not a `#', i.e., that does not start with a comment.

       Remaining arguments are placed in the argv shell variable.

   Startup and shutdown
       A  login  shell	begins	by  executing  commands  from the system files
       /etc/csh.cshrc and /etc/csh.login.   It	then  executes	commands  from
       files  in  the  user's  home  directory:  first	~/.tcshrc  (+)	or, if
       ~/.tcshrc is not found, ~/.cshrc, then ~/.history (or the value of  the
       histfile shell variable), then ~/.login, and finally ~/.cshdirs (or the
       value of  the  dirsfile	shell  variable)  (+).	 The  shell  may  read
       /etc/csh.login  before  instead	of  after /etc/csh.cshrc, and ~/.login
       before instead of after ~/.tcshrc or ~/.cshrc  and  ~/.history,	if  so
       compiled; see the version shell variable. (+)

       Non-login  shells read only /etc/csh.cshrc and ~/.tcshrc or ~/.cshrc on
       startup.

       For examples of startup	files,	please	consult  http://tcshrc.source-
       forge.net.

       Commands  like  stty(1)	and  tset(1),  which need be run only once per
       login, usually go in one's ~/.login file.  Users who need  to  use  the
       same  set  of  files with both csh(1) and tcsh can have only a ~/.cshrc
       which checks for the existence of the tcsh shell variable (q.v.) before
       using  tcsh-specific  commands,	or  can  have  both  a	~/.cshrc and a
       ~/.tcshrc which sources (see the builtin command) ~/.cshrc.   The  rest
       of  this manual uses `~/.tcshrc' to mean `~/.tcshrc or, if ~/.tcshrc is

       One can log out by typing `^D' on an empty line, `logout' or `login' or
       via the shell's autologout mechanism (see the  autologout  shell  vari-
       able).  When a login shell terminates it sets the logout shell variable
       to `normal' or `automatic' as appropriate, then executes commands  from
       the  files  /etc/csh.logout  and  ~/.logout.  The shell may drop DTR on
       logout if so compiled; see the version shell variable.

       The names of the system login and logout files vary from system to sys-
       tem for compatibility with different csh(1) variants; see FILES.

   Editing
       We  first describe The command-line editor.  The Completion and listing
       and Spelling correction sections describe  two  sets  of  functionality
       that  are  implemented  as  editor commands but which deserve their own
       treatment.  Finally, Editor commands lists  and	describes  the	editor
       commands specific to the shell and their default bindings.

   The command-line editor (+)
       Command-line  input  can  be edited using key sequences much like those
       used in GNU Emacs or vi(1).  The editor is active only  when  the  edit
       shell  variable	is  set, which it is by default in interactive shells.
       The bindkey builtin can display and change key  bindings.   Emacs-style
       key  bindings are used by default (unless the shell was compiled other-
       wise; see the version shell variable), but bindkey can change  the  key
       bindings to vi-style bindings en masse.

       The  shell always binds the arrow keys (as defined in the TERMCAP envi-
       ronment variable) to

	   down    down-history
	   up	   up-history
	   left    backward-char
	   right   forward-char

       unless doing so would alter another single-character binding.  One  can
       set  the  arrow	key escape sequences to the empty string with settc to
       prevent these bindings.	The ANSI/VT100 sequences for  arrow  keys  are
       always bound.

       Other  key  bindings are, for the most part, what Emacs and vi(1) users
       would expect and can easily be displayed by bindkey,  so  there	is  no
       need to list them here.	Likewise, bindkey can list the editor commands
       with a short description of each.

       Note that editor commands do not have the same notion of a ``word''  as
       does  the  shell.   The editor delimits words with any non-alphanumeric
       characters not in the shell variable wordchars, while the shell	recog-
       nizes  only whitespace and some of the characters with special meanings
       to it, listed under Lexical structure.

   Completion and listing (+)
       The shell is often able to complete words when given a unique abbrevia-
       tion.  Type part of a word (for example `ls /usr/lost') and hit the tab
       key to run the complete-word editor command.  The shell	completes  the
       filename  `/usr/lost'  to  `/usr/lost+found/', replacing the incomplete
       word with the complete word in the input buffer.   (Note  the  terminal
       `/';  completion  adds  a `/' to the end of completed directories and a
       Completion works anywhere in the line, not at just the  end;  completed
       text  pushes the rest of the line to the right.	Completion in the mid-
       dle of a word often results in leftover characters to the right of  the
       cursor that need to be deleted.

       Commands  and  variables  can  be  completed in much the same way.  For
       example, typing `em[tab]' would complete `em' to `emacs' if emacs  were
       the  only  command  on your system beginning with `em'.	Completion can
       find a command in any directory in path or if given  a  full  pathname.
       Typing  `echo  $ar[tab]'  would	complete  `$ar' to `$argv' if no other
       variable began with `ar'.

       The shell parses the input buffer to determine  whether	the  word  you
       want  to  complete  should be completed as a filename, command or vari-
       able.  The first word in the buffer and the first word  following  `;',
       `|',  `|&',  `&&' or `||' is considered to be a command.  A word begin-
       ning with `$' is considered to be a variable.  Anything else is a file-
       name.  An empty line is `completed' as a filename.

       You  can  list the possible completions of a word at any time by typing
       `^D' to run the delete-char-or-list-or-eof editor command.   The  shell
       lists  the  possible completions using the ls-F builtin (q.v.)  and re-
       prints the prompt and unfinished command line, for example:

	   > ls /usr/l[^D]
	   lbin/       lib/	   local/      lost+found/
	   > ls /usr/l

       If the autolist shell variable is set, the shell  lists	the  remaining
       choices (if any) whenever completion fails:

	   > set autolist
	   > nm /usr/lib/libt[tab]
	   libtermcap.a@ libtermlib.a@
	   > nm /usr/lib/libterm

       If autolist is set to `ambiguous', choices are listed only when comple-
       tion fails and adds no new characters to the word being completed.

       A filename to be completed can contain variables, your own  or  others'
       home  directories  abbreviated with `~' (see Filename substitution) and
       directory stack entries abbreviated with `=' (see Directory stack  sub-
       stitution).  For example,

	   > ls ~k[^D]
	   kahn    kas	   kellogg
	   > ls ~ke[tab]
	   > ls ~kellogg/

       or

	   > set local = /usr/local
	   > ls $lo[tab]
	   > ls $local/[^D]
	   bin/ etc/ lib/ man/ src/
	   > ls $local/

       Note  that  variables  can also be expanded explicitly with the expand-
       listed under delete-char-or-list-or-eof) can be bound to `^D' with  the
       bindkey builtin command if so desired.

       The complete-word-fwd and complete-word-back editor commands (not bound
       to any keys by default) can be used to cycle up and  down  through  the
       list  of possible completions, replacing the current word with the next
       or previous word in the list.

       The shell variable fignore can be set to  a  list  of  suffixes	to  be
       ignored by completion.  Consider the following:

	   > ls
	   Makefile	   condiments.h~   main.o	   side.c
	   README	   main.c	   meal 	   side.o
	   condiments.h    main.c~
	   > set fignore = (.o \~)
	   > emacs ma[^D]
	   main.c   main.c~  main.o
	   > emacs ma[tab]
	   > emacs main.c

       `main.c~'  and  `main.o'  are  ignored by completion (but not listing),
       because they end in suffixes in fignore.  Note that a `\' was needed in
       front  of  `~'  to  prevent it from being expanded to home as described
       under Filename substitution.  fignore is ignored if only one completion
       is possible.

       If  the	complete  shell  variable  is  set to `enhance', completion 1)
       ignores case and 2) considers periods, hyphens  and  underscores  (`.',
       `-'  and  `_')  to be word separators and hyphens and underscores to be
       equivalent.  If you had the following files

	   comp.lang.c	    comp.lang.perl   comp.std.c++
	   comp.lang.c++    comp.std.c

       and typed `mail -f c.l.c[tab]', it  would  be  completed  to  `mail  -f
       comp.lang.c',  and  ^D  would  list  `comp.lang.c' and `comp.lang.c++'.
       `mail -f c..c++[^D]' would  list  `comp.lang.c++'  and  `comp.std.c++'.
       Typing `rm a--file[^D]' in the following directory

	   A_silly_file    a-hyphenated-file	another_silly_file

       would  list  all  three	files, because case is ignored and hyphens and
       underscores are equivalent.  Periods, however, are  not	equivalent  to
       hyphens or underscores.

       Completion  and	listing are affected by several other shell variables:
       recexact can be set to complete on the shortest possible unique	match,
       even if more typing might result in a longer match:

	   > ls
	   fodder   foo      food     foonly
	   > set recexact
	   > rm fo[tab]

       just beeps, because `fo' could expand to `fod' or `foo', but if we type
       another `o',

       ically  after  one hits `return'.  matchbeep can be set to make comple-
       tion beep or not beep in a variety of situations, and nobeep can be set
       to  never  beep	at  all.   nostat  can be set to a list of directories
       and/or patterns that match directories to prevent the completion mecha-
       nism from stat(2)ing those directories.	listmax and listmaxrows can be
       set to limit the number of  items  and  rows  (respectively)  that  are
       listed  without asking first.  recognize_only_executables can be set to
       make the shell list only executables when listing commands, but	it  is
       quite slow.

       Finally, the complete builtin command can be used to tell the shell how
       to complete words other than filenames, commands and  variables.   Com-
       pletion	and listing do not work on glob-patterns (see Filename substi-
       tution), but the list-glob  and	expand-glob  editor  commands  perform
       equivalent functions for glob-patterns.

   Spelling correction (+)
       The shell can sometimes correct the spelling of filenames, commands and
       variable names as well as completing and listing them.

       Individual words can be spelling-corrected with the  spell-word	editor
       command (usually bound to M-s and M-S) and the entire input buffer with
       spell-line (usually bound to M-$).  The correct shell variable  can  be
       set to `cmd' to correct the command name or `all' to correct the entire
       line each time return is typed, and autocorrect can be set  to  correct
       the word to be completed before each completion attempt.

       When  spelling correction is invoked in any of these ways and the shell
       thinks that any part of the command line is misspelled, it prompts with
       the corrected line:

	   > set correct = cmd
	   > lz /usr/bin
	   CORRECT>ls /usr/bin (y|n|e|a)?

       One can answer `y' or space to execute the corrected line, `e' to leave
       the uncorrected command in the input buffer, `a' to abort  the  command
       as if `^C' had been hit, and anything else to execute the original line
       unchanged.

       Spelling correction recognizes user-defined completions (see  the  com-
       plete  builtin  command).   If  an input word in a position for which a
       completion is defined resembles a word in the completion list, spelling
       correction  registers  a  misspelling and suggests the latter word as a
       correction.  However, if the input word does not match any of the  pos-
       sible  completions for that position, spelling correction does not reg-
       ister a misspelling.

       Like completion, spelling correction works anywhere in the line,  push-
       ing  the rest of the line to the right and possibly leaving extra char-
       acters to the right of the cursor.

       Beware: spelling correction is not  guaranteed  to  work  the  way  one
       intends,  and  is  provided mostly as an experimental feature.  Sugges-
       tions and improvements are welcome.

   Editor commands (+)
       `bindkey' lists	key  bindings  and  `bindkey  -l'  lists  and  briefly
       ters by default are bound to both lower- and uppercase letters for con-
       venience.

       complete-word (tab)
	       Completes a word as described under Completion and listing.

       complete-word-back (not bound)
	       Like complete-word-fwd, but steps up from the end of the  list.

       complete-word-fwd (not bound)
	       Replaces  the  current  word with the first word in the list of
	       possible completions.  May be repeated to step down through the
	       list.   At the end of the list, beeps and reverts to the incom-
	       plete word.

       complete-word-raw (^X-tab)
	       Like complete-word, but ignores user-defined completions.

       copy-prev-word (M-^_)
	       Copies the previous word in the current	line  into  the  input
	       buffer.	See also insert-last-word.

       dabbrev-expand (M-/)
	       Expands	the  current word to the most recent preceding one for
	       which the current is a leading substring, wrapping  around  the
	       history	list  (once)  if  necessary.  Repeating dabbrev-expand
	       without any intervening typing changes  to  the	next  previous
	       word etc., skipping identical matches much like history-search-
	       backward does.

       delete-char (not bound)
	       Deletes the character under the cursor.	See also  delete-char-
	       or-list-or-eof.

       delete-char-or-eof (not bound)
	       Does  delete-char  if  there is a character under the cursor or
	       end-of-file on an empty line.  See also delete-char-or-list-or-
	       eof.

       delete-char-or-list (not bound)
	       Does  delete-char  if  there is a character under the cursor or
	       list-choices at the end of the line.  See also  delete-char-or-
	       list-or-eof.

       delete-char-or-list-or-eof (^D)
	       Does  delete-char  if  there  is  a character under the cursor,
	       list-choices at the end of the line or end-of-file on an  empty
	       line.  See also those three commands, each of which does only a
	       single action, and delete-char-or-eof, delete-char-or-list  and
	       list-or-eof,  each  of  which  does  a different two out of the
	       three.

       down-history (down-arrow, ^N)
	       Like up-history, but steps down, stopping at the original input
	       line.

       end-of-file (not bound)
	       Signals	an  end  of file, causing the shell to exit unless the

       expand-glob (^X-*)
	       Expands	the glob-pattern to the left of the cursor.  See File-
	       name substitution.

       expand-line (not bound)
	       Like expand-history, but expands history substitutions in  each
	       word in the input buffer,

       expand-variables (^X-$)
	       Expands	the  variable to the left of the cursor.  See Variable
	       substitution.

       history-search-backward (M-p, M-P)
	       Searches backwards through  the	history  list  for  a  command
	       beginning  with	the current contents of the input buffer up to
	       the cursor and copies it into the  input  buffer.   The	search
	       string  may  be a glob-pattern (see Filename substitution) con-
	       taining `*', `?', `[]' or `{}'.	 up-history  and  down-history
	       will  proceed  from  the appropriate point in the history list.
	       Emacs mode only.  See also history-search-forward and i-search-
	       back.

       history-search-forward (M-n, M-N)
	       Like history-search-backward, but searches forward.

       i-search-back (not bound)
	       Searches  backward  like  history-search-backward,  copies  the
	       first match into the input buffer with the cursor positioned at
	       the  end of the pattern, and prompts with `bck: ' and the first
	       match.  Additional  characters  may  be	typed  to  extend  the
	       search,	i-search-back  may be typed to continue searching with
	       the same pattern, wrapping around the history  list  if	neces-
	       sary,  (i-search-back  must  be bound to a single character for
	       this to work) or one of the following special characters may be
	       typed:

		   ^W	   Appends  the  rest  of the word under the cursor to
			   the search pattern.
		   delete (or any character bound to backward-delete-char)
			   Undoes the effect of the last character  typed  and
			   deletes  a  character  from	the  search pattern if
			   appropriate.
		   ^G	   If the previous search was successful,  aborts  the
			   entire  search.  If not, goes back to the last suc-
			   cessful search.
		   escape  Ends the search, leaving the current  line  in  the
			   input buffer.

	       Any other character not bound to self-insert-command terminates
	       the search, leaving the current line in the input  buffer,  and
	       is then interpreted as normal input.  In particular, a carriage
	       return causes the current line  to  be  executed.   Emacs  mode
	       only.  See also i-search-fwd and history-search-backward.

       i-search-fwd (not bound)
	       Like i-search-back, but searches forward.

       insert-last-word (M-_)
       list-choices-raw (^X-^D)
	       Like list-choices, but ignores user-defined completions.

       list-glob (^X-g, ^X-G)
	       Lists (via the ls-F builtin) matches to the  glob-pattern  (see
	       Filename substitution) to the left of the cursor.

       list-or-eof (not bound)
	       Does  list-choices  or  end-of-file on an empty line.  See also
	       delete-char-or-list-or-eof.

       magic-space (not bound)
	       Expands history substitutions in the current line, like expand-
	       history,  and  inserts  a space.  magic-space is designed to be
	       bound to the space bar, but is not bound by default.

       normalize-command (^X-?)
	       Searches for the current word in PATH  and,  if	it  is	found,
	       replaces  it  with  the	full  path to the executable.  Special
	       characters are quoted.  Aliases are  expanded  and  quoted  but
	       commands  within  aliases are not.  This command is useful with
	       commands that take commands as arguments, e.g., `dbx'  and  `sh
	       -x'.

       normalize-path (^X-n, ^X-N)
	       Expands	the  current word as described under the `expand' set-
	       ting of the symlinks shell variable.

       overwrite-mode (unbound)
	       Toggles between input and overwrite modes.

       run-fg-editor (M-^Z)
	       Saves the current input line and looks for a stopped job with a
	       name  equal  to the last component of the file name part of the
	       EDITOR or VISUAL environment variables, or, if neither is  set,
	       `ed'  or  `vi'.	 If such a job is found, it is restarted as if
	       `fg %job' had been typed.  This is  used  to  toggle  back  and
	       forth between an editor and the shell easily.  Some people bind
	       this command to `^Z' so they can do this even more easily.

       run-help (M-h, M-H)
	       Searches for documentation on the current  command,  using  the
	       same  notion  of  `current command' as the completion routines,
	       and prints it.  There is no way to use  a  pager;  run-help  is
	       designed  for  short help files.  If the special alias helpcom-
	       mand is defined, it is run with the  command  name  as  a  sole
	       argument.   Else,  documentation should be in a file named com-
	       mand.help, command.1, command.6, command.8  or  command,  which
	       should  be  in one of the directories listed in the HPATH envi-
	       ronment variable.  If there is more than one help file only the
	       first is printed.

       self-insert-command (text characters)
	       In  insert mode (the default), inserts the typed character into
	       the input line after the character under the cursor.  In  over-
	       write  mode,  replaces  the character under the cursor with the
	       typed character.  The input mode is normally preserved  between
	       lines,  but the inputmode shell variable can be set to `insert'
	       with  a	character  bound  to  sequence-lead-in are effectively
	       bound to undefined-key unless bound to another command.

       spell-line (M-$)
	       Attempts to correct the spelling of  each  word	in  the  input
	       buffer,	like spell-word, but ignores words whose first charac-
	       ter is one of `-', `!', `^' or `%', or which contain  `\',  `*'
	       or  `?', to avoid problems with switches, substitutions and the
	       like.  See Spelling correction.

       spell-word (M-s, M-S)
	       Attempts to  correct  the  spelling  of	the  current  word  as
	       described  under Spelling correction.  Checks each component of
	       a word which appears to be a pathname.

       toggle-literal-history (M-r, M-R)
	       Expands or  `unexpands'	history  substitutions	in  the  input
	       buffer.	See also expand-history and the autoexpand shell vari-
	       able.

       undefined-key (any unbound key)
	       Beeps.

       up-history (up-arrow, ^P)
	       Copies the previous entry in the history list  into  the  input
	       buffer.	If histlit is set, uses the literal form of the entry.
	       May be repeated to step up through the history  list,  stopping
	       at the top.

       vi-search-back (?)
	       Prompts	with `?' for a search string (which may be a glob-pat-
	       tern, as with history-search-backward),	searches  for  it  and
	       copies it into the input buffer.  The bell rings if no match is
	       found.  Hitting return ends the	search	and  leaves  the  last
	       match  in the input buffer.  Hitting escape ends the search and
	       executes the match.  vi mode only.

       vi-search-fwd (/)
	       Like vi-search-back, but searches forward.

       which-command (M-?)
	       Does a which (see the description of the  builtin  command)  on
	       the first word of the input buffer.

       yank-pop (M-y)
	       When  executed  immediately  after  a yank or another yank-pop,
	       replaces the yanked string with the next previous  string  from
	       the  killring.  This  also has the effect of rotating the kill-
	       ring, such  that  this  string  will  be  considered  the  most
	       recently  killed  by  a	later yank command. Repeating yank-pop
	       will cycle through the killring any number of times.

   Lexical structure
       The shell splits input lines into words at blanks and tabs.   The  spe-
       cial  characters  `&', `|', `;', `<', `>', `(', and `)' and the doubled
       characters `&&', `||', `<<' and `>>' are always separate words, whether
       or not they are surrounded by whitespace.

       newline	preceded  by a `\' is equivalent to a blank, but inside quotes
       this sequence results in a newline.

       Furthermore, all Substitutions (see below) except History  substitution
       can  be	prevented  by  enclosing  the strings (or parts of strings) in
       which they appear with single quotes or by quoting the crucial  charac-
       ter(s) (e.g., `$' or ``' for Variable substitution or Command substitu-
       tion respectively) with `\'.   (Alias  substitution  is	no  exception:
       quoting	in any way any character of a word for which an alias has been
       defined prevents substitution of the alias.  The usual way  of  quoting
       an  alias  is  to precede it with a backslash.) History substitution is
       prevented by backslashes but not by single quotes.  Strings quoted with
       double  or  backward  quotes  undergo Variable substitution and Command
       substitution, but other substitutions are prevented.

       Text inside single or double quotes becomes a single word (or  part  of
       one).   Metacharacters  in these strings, including blanks and tabs, do
       not form separate words.  Only in one special case (see Command substi-
       tution  below)  can a double-quoted string yield parts of more than one
       word; single-quoted strings never do.   Backward  quotes  are  special:
       they  signal Command substitution (q.v.), which may result in more than
       one word.

       Quoting complex strings, particularly strings which themselves  contain
       quoting characters, can be confusing.  Remember that quotes need not be
       used as they are in human writing!  It may be easier to	quote  not  an
       entire  string,	but only those parts of the string which need quoting,
       using different types of quoting to do so if appropriate.

       The backslash_quote shell variable (q.v.) can  be  set  to  make  back-
       slashes	always	quote  `\',  `'',  and `"'.  (+) This may make complex
       quoting tasks easier, but it can cause syntax errors in csh(1) scripts.

   Substitutions
       We  now	describe the various transformations the shell performs on the
       input in the order in which they occur.	We note in  passing  the  data
       structures  involved  and the commands and variables which affect them.
       Remember that substitutions can be prevented by	quoting  as  described
       under Lexical structure.

   History substitution
       Each  command,  or  ``event'',  input from the terminal is saved in the
       history list.  The previous command is always saved,  and  the  history
       shell  variable can be set to a number to save that many commands.  The
       histdup shell variable can be set to not save duplicate events or  con-
       secutive duplicate events.

       Saved  commands	are  numbered sequentially from 1 and stamped with the
       time.  It is not usually necessary to use event numbers, but  the  cur-
       rent  event  number can be made part of the prompt by placing an `!' in
       the prompt shell variable.

       The shell actually saves history in expanded and  literal  (unexpanded)
       forms.  If the histlit shell variable is set, commands that display and
       store history use the literal form.

       The history builtin command can print, store in	a  file,  restore  and
       clear the history list at any time, and the savehist and histfile shell

       History	substitutions  begin  with  the character `!'.	They may begin
       anywhere in the input stream, but they do not nest.   The  `!'  may  be
       preceded  by  a	`\' to prevent its special meaning; for convenience, 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  later.   The
       characters  used  to  signal  history substitution (`!' and `^') can be
       changed by setting the histchars shell variable.  Any input line  which
       contains a history substitution is printed before it is executed.

       A history substitution may have an ``event specification'', which indi-
       cates the event from which words are to be  taken,  a  ``word  designa-
       tor'',  which  selects particular words from the chosen event, and/or a
       ``modifier'', which manipulates the selected words.

       An event specification can be

	   n	   A number, referring to a particular event
	   -n	   An offset, referring to the	event  n  before  the  current
		   event
	   #	   The	current  event.   This	should	be  used  carefully in
		   csh(1), where there is no check for recursion.  tcsh allows
		   10 levels of recursion.  (+)
	   !	   The previous event (equivalent to `-1')
	   s	   The	most  recent  event  whose  first word begins with the
		   string s
	   ?s?	   The most recent event which contains  the  string  s.   The
		   second  `?' can be omitted if it is immediately followed by
		   a newline.

       For example, consider this bit of someone's history list:

	    9  8:30    nroff -man wumpus.man
	   10  8:31    cp wumpus.man wumpus.man.old
	   11  8:36    vi wumpus.man
	   12  8:37    diff wumpus.man.old wumpus.man

       The commands are shown with their event numbers and time  stamps.   The
       current	event,	which we haven't typed in yet, is event 13.  `!11' and
       `!-2' refer to event 11.  `!!' refers to the previous event, 12.   `!!'
       can  be	abbreviated  `!'  if  it  is followed by `:' (`:' is described
       below).	`!n' refers to event 9, which begins with `n'.	`!?old?'  also
       refers  to event 12, which contains `old'.  Without word designators or
       modifiers history references simply expand to the entire event,	so  we
       might  type  `!cp'  to redo the copy command or `!!|more' if the `diff'
       output scrolled off the top of the screen.

       History references may be insulated  from  the  surrounding  text  with
       braces  if  necessary.	For  example, `!vdoc' would look for a command
       beginning with  `vdoc',	and,  in  this	example,  not  find  one,  but
       `!{v}doc'  would  expand  unambiguously to `vi wumpus.mandoc'.  Even in
       braces, history substitutions do not nest.

       (+) While csh(1) expands, for example, `!3d' to event 3 with the letter
       `d'  appended  to  it, tcsh expands it to the last event beginning with
       `3d'; only completely numeric arguments are treated as  event  numbers.
       This  makes  it	possible  to recall events beginning with numbers.  To

	   0	   The first (command) word
	   n	   The nth argument
	   ^	   The first argument, equivalent to `1'
	   $	   The last argument
	   %	   The word matched by an ?s? search
	   x-y	   A range of words
	   -y	   Equivalent to `0-y'
	   *	   Equivalent to `^-$', but returns nothing if the event  con-
		   tains only 1 word
	   x*	   Equivalent to `x-$'
	   x-	   Equivalent to `x*', but omitting the last word (`$')

       Selected  words	are inserted into the command line separated by single
       blanks.	For example, the `diff' command in the previous example  might
       have been typed as `diff !!:1.old !!:1' (using `:1' to select the first
       argument from the previous event) or `diff !-2:2 !-2:1' to  select  and
       swap  the arguments from the `cp' command.  If we didn't care about the
       order of the `diff' we might have said `diff !-2:1-2' or  simply  `diff
       !-2:*'.	 The  `cp'  command  might  have  been	written `cp wumpus.man
       !#:1.old', using `#' to refer to the current event.  `!n:-  hurkle.man'
       would  reuse the first two words from the `nroff' command to say `nroff
       -man hurkle.man'.

       The `:' separating the event specification from the word designator can
       be omitted if the argument selector begins with a `^', `$', `*', `%' or
       `-'.  For example, our `diff' command might  have  been	`diff  !!^.old
       !!^'  or, equivalently, `diff !!$.old !!$'.  However, if `!!' is abbre-
       viated `!', an argument selector beginning with `-' will be interpreted
       as an event specification.

       A  history reference may have a word designator but no event specifica-
       tion.  It then references the previous command.	Continuing our	`diff'
       example,  we  could  have  said	simply `diff !^.old !^' or, to get the
       arguments in the opposite order, just `diff !*'.

       The word or words in a history reference  can  be  edited,  or  ``modi-
       fied'',	by following it with one or more modifiers, each preceded by a
       `:':

	   h	   Remove a trailing pathname component, leaving the head.
	   t	   Remove all leading pathname components, leaving the tail.
	   r	   Remove a filename extension `.xxx', leaving the root  name.
	   e	   Remove all but the extension.
	   u	   Uppercase the first lowercase letter.
	   l	   Lowercase the first uppercase letter.
	   s/l/r/  Substitute  l  for  r.   l is simply a string like r, not a
		   regular expression as in the eponymous ed(1) command.   Any
		   character  may  be used as the delimiter in place of `/'; a
		   `\' can be used to quote the delimiter inside l and r.  The
		   character  `&'  in  the r is replaced by l; `\' also quotes
		   `&'.  If l is empty (``''), the l from a previous substitu-
		   tion  or the s from a previous `?s?' event specification is
		   used.  The trailing delimiter may be omitted if it is imme-
		   diately followed by a newline.
	   &	   Repeat the previous substitution.
	   g	   Apply the following modifier once to each word.
	   a (+)   Apply the following modifier as many times as possible to a
		   single word.  `a' and `g' can be used together to  apply  a

       Modifiers are applied to only the first modifiable word (unless `g'  is
       used).  It is an error for no word to be modifiable.

       For  example,  the `diff' command might have been written as `diff wum-
       pus.man.old !#^:r', using `:r' to remove `.old' from the first argument
       on  the	same  line (`!#^').  We could say `echo hello out there', then
       `echo !*:u' to capitalize `hello', `echo !*:au' to say it out loud,  or
       `echo  !*:agu'  to really shout.  We might follow `mail -s "I forgot my
       password" rot' with `!:s/rot/root' to correct the  spelling  of	`root'
       (but see Spelling correction for a different approach).

       There is a special abbreviation for substitutions.  `^', when it is the
       first character on an input line, is equivalent	to  `!:s^'.   Thus  we
       might have said `^rot^root' to make the spelling correction in the pre-
       vious example.  This is the only history substitution  which  does  not
       explicitly begin with `!'.

       (+) In csh as such, only one modifier may be applied to each history or
       variable expansion.  In tcsh, more than one may be used, for example

	   % mv wumpus.man /usr/man/man1/wumpus.1
	   % man !$:t:r
	   man wumpus

       In csh, the result would be `wumpus.1:r'.  A substitution followed by a
       colon may need to be insulated from it with braces:

	   > mv a.out /usr/games/wumpus
	   > setenv PATH !$:h:$PATH
	   Bad ! modifier: $.
	   > setenv PATH !{-2$:h}:$PATH
	   setenv PATH /usr/games:/bin:/usr/bin:.

       The  first attempt would succeed in csh but fails in tcsh, because tcsh
       expects another modifier after the second colon rather than `$'.

       Finally, history can be accessed through the editor as well as  through
       the  substitutions  just described.  The up- and down-history, history-
       search-backward and -forward, i-search-back  and  -fwd,	vi-search-back
       and  -fwd,  copy-prev-word  and insert-last-word editor commands search
       for events in the history list and copy them  into  the	input  buffer.
       The toggle-literal-history editor command switches between the expanded
       and literal forms of history lines in the input buffer.	expand-history
       and expand-line expand history substitutions in the current word and in
       the entire input buffer respectively.

   Alias substitution
       The shell maintains a list of aliases  which  can  be  set,  unset  and
       printed	by  the  alias	and unalias commands.  After a command line is
       parsed into simple commands (see Commands) the first word of each  com-
       mand,  left-to-right, is checked to see if it has an alias.  If so, the
       first word is replaced by the alias.  If the alias contains  a  history
       reference, it undergoes History substitution (q.v.) as though the orig-
       inal command were the previous input line.  If the alias does not  con-
       tain a history reference, the argument list is left untouched.

       Thus  if  the  alias  for `ls' were `ls -l' the command `ls /usr' would
       in the previous example) it is flagged to prevent a loop.  Other  loops
       are detected and cause an error.

       Some aliases are referred to by the shell; see Special aliases.

   Variable substitution
       The  shell  maintains a list of variables, each of which has as value a
       list of zero or more words.  The values of shell variables can be  dis-
       played  and  changed with the set and unset commands.  The system main-
       tains its own list of ``environment'' variables.   These  can  be  dis-
       played and changed with printenv, setenv and unsetenv.

       (+)  Variables  may  be	made read-only with `set -r' (q.v.)  Read-only
       variables may not be modified or unset; attempting to do so will  cause
       an  error.  Once made read-only, a variable cannot be made writable, so
       `set -r' should be used with caution.  Environment variables cannot  be
       made read-only.

       Some  variables	are  set  by  the  shell  or  referred	to by it.  For
       instance, the argv variable is an image of the shell's  argument  list,
       and  words  of  this  variable's value are referred to in special ways.
       Some of the variables referred to by the shell are toggles;  the  shell
       does  not  care	what their value is, only whether they are set or not.
       For instance, the verbose variable is a	toggle	which  causes  command
       input  to  be  echoed.	The -v command line option sets this variable.
       Special shell variables lists all variables which are  referred	to  by
       the shell.

       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 considered to be zero, and the second and subsequent words of multi-
       word values 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	always	occurs, and within `''s where it never
       occurs.	Strings quoted by ``' are interpreted later (see Command  sub-
       stitution  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  vari-
       able  substitution  may eventually be command and filename substituted.
       Within `"', a variable whose value consists of multiple	words  expands
       to a (portion of a) single word, with the words of the variable's value
       separated by blanks.  When the `:q' modifier is applied to a  substitu-
       tion  the  variable  will expand to multiple words with each word sepa-
       rated by a blank and quoted to prevent later command or	filename  sub-
	       rated by a blank.  Braces insulate name from following  charac-
	       ters 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 character is considered a letter.  If
	       name is not a shell variable, but is set  in  the  environment,
	       then  that  value  is returned (but `:' modifiers and the other
	       forms given below are not available in this case).
       $name[selector]
       ${name[selector]}
	       Substitutes only the selected words from  the  value  of  name.
	       The  selector  is subjected to `$' substitution and may consist
	       of a single number or two numbers  separated  by  a  `-'.   The
	       first word of a variable's 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 defaults 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.
       $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', which is equivalent to `$argv[*]'.

       The `:' modifiers described  under  History  substitution,  except  for
       `:p',  can be applied to the substitutions above.  More than one may be
       used.  (+) Braces may be needed to  insulate  a	variable  substitution
       from a literal colon just as with History substitution (q.v.); any mod-
       ifiers must appear within the braces.

       The following substitutions can 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.  Always `0' in interactive shells.
       $#name
       ${#name}
	       Substitutes the number of words in name.
       $#      Equivalent to `$#argv'.	(+)
       $%name
       ${%name}
	       Substitutes the number of characters in name.  (+)
       $%number
       ${%number}
	       Substitutes the number of characters in $argv[number].  (+)
       $?      Equivalent to `$status'.  (+)
       $$      Substitutes the (decimal) process number of the (parent) shell.
       $!      Substitutes the (decimal) process number of the last background
	       process started by this shell.  (+)
       $_      Substitutes the command line of the last command executed.  (+)
       $<      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.  (+) While csh always quotes $<, as
	       if  it  were equivalent to `$<:q', tcsh does not.  Furthermore,
	       when tcsh is waiting for a line to be typed the user  may  type
	       an  interrupt  to interrupt the sequence into which the line is

       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 occurs very late, after input-
       output redirection is performed, and in a child of the main shell.

   Command substitution
       Command substitution is indicated by a command enclosed	in  ``'.   The
       output  from  such  a  command is broken into separate words at blanks,
       tabs and newlines, and null words are discarded.  The output  is  vari-
       able and command substituted and put in place of the original string.

       Command	substitutions  inside  double  quotes  (`"') retain blanks and
       tabs; only newlines force new words.  The single final newline does not
       force  a  new word in any case.	It is thus possible for a command sub-
       stitution to yield only part of a word, even if the command  outputs  a
       complete line.

   Filename substitution
       If a word contains any of the characters `*', `?', `[' or `{' or begins
       with the character `~' it is a  candidate  for  filename  substitution,
       also  known  as	``globbing''.  This word is then regarded as a pattern
       (``glob-pattern''), and replaced with an alphabetically sorted list  of
       file names which match the pattern.

       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 charac-
       ters, including the null string.  The character `?' matches any	single
       character.   The  sequence  `[...]'  matches  any one of the characters
       enclosed.  Within `[...]',  a  pair  of	characters  separated  by  `-'
       matches any character lexically between the two.

       (+)  Some  glob-patterns  can be negated: The sequence `[^...]' matches
       any single character not specified by the characters and/or  ranges  of
       characters in the braces.

       An entire glob-pattern can also be negated with `^':

	   > echo *
	   bang crash crunch ouch
	   > echo ^cr*
	   bang ouch

       Glob-patterns  which  do not use `?', `*', or `[]' or which use `{}' or
       `~' (below) are not negated correctly.

       The metanotation `a{b,c,d}e' is a shorthand for `abe ace  ade'.	 Left-
       to-right  order	is preserved: `/usr/source/s1/{oldls,ls}.c' expands to
       `/usr/source/s1/oldls.c /usr/source/s1/ls.c'.  The results  of  matches
       are   sorted  separately  at  a	low  level  to	preserve  this	order:
       `../{memo,*box}' might expand to `../memo ../box ../mbox'.  (Note  that
       `memo'  was not sorted with the results of matching `*box'.)  It is not
       an error when this construct expands to files which do not  exist,  but
       it  is  possible  to  get an error from a command to which the expanded
       list is passed.	This construct may be nested.  As a special  case  the
       words `{', `}' and `{}' are passed undisturbed.

       The  character `~' at the beginning of a filename refers to home direc-
       /usr/man:/usr/local/man:~/lib/man' does not, therefore, do home	direc-
       tory substitution as one might hope.

       It is an error for a glob-pattern containing `*', `?', `[' or `~', with
       or without `^', not to match any files.	However, only one pattern in a
       list  of  glob-patterns	must  match a file (so that, e.g., `rm *.a *.c
       *.o' would fail only if there were no files in  the  current  directory
       ending  in `.a', `.c', or `.o'), and if the nonomatch shell variable is
       set a pattern (or list of  patterns)  which  matches  nothing  is  left
       unchanged rather than causing an error.

       The  noglob shell variable can be set to prevent filename substitution,
       and the expand-glob editor command, normally bound to  `^X-*',  can  be
       used to interactively expand individual filename substitutions.

   Directory stack substitution (+)
       The  directory stack is a list of directories, numbered from zero, used
       by the pushd, popd and dirs builtin commands (q.v.).  dirs  can	print,
       store in a file, restore and clear the directory stack at any time, and
       the savedirs and dirsfile shell variables  can  be  set	to  store  the
       directory  stack  automatically on logout and restore it on login.  The
       dirstack shell variable can be examined to see the directory stack  and
       set to put arbitrary directories into the directory stack.

       The character `=' followed by one or more digits expands to an entry in
       the directory stack.  The special case `=-' expands to the last	direc-
       tory in the stack.  For example,

	   > dirs -v
	   0	   /usr/bin
	   1	   /usr/spool/uucp
	   2	   /usr/accts/sys
	   > echo =1
	   /usr/spool/uucp
	   > echo =0/calendar
	   /usr/bin/calendar
	   > echo =-
	   /usr/accts/sys

       The  noglob  and  nonomatch  shell variables and the expand-glob editor
       command apply to directory stack as well as filename substitutions.

   Other substitutions (+)
       There  are  several  more  transformations  involving  filenames,   not
       strictly related to the above but mentioned here for completeness.  Any
       filename may be expanded to a full  path  when  the  symlinks  variable
       (q.v.)  is  set	to `expand'.  Quoting prevents this expansion, and the
       normalize-path editor command does it on demand.  The normalize-command
       editor  command	expands  commands  in  PATH into full paths on demand.
       Finally, cd and pushd  interpret  `-'  as  the  old  working  directory
       (equivalent  to the shell variable owd).  This is not a substitution at
       all, but an abbreviation recognized by only those  commands.   Nonethe-
       less, it too can be prevented by quoting.

   Commands
       The  next  three  sections describe how the shell executes commands and
       deals with their input and output.

       joined  into  sequences with `||' or `&&', indicating, as in the C lan-
       guage, that the second is to be executed only if  the  first  fails  or
       succeeds respectively.

       A  simple  command,  pipeline or sequence may be placed in parentheses,
       `()', to form a simple command, which may in turn be a component  of  a
       pipeline  or sequence.  A command, pipeline or sequence can be executed
       without waiting for it to terminate by following it with an `&'.

   Builtin and non-builtin command execution
       Builtin commands are executed within the shell.	If any component of  a
       pipeline except the last is a builtin command, the pipeline is executed
       in a subshell.

       Parenthesized commands are always executed in a subshell.

	   (cd; pwd); pwd

       thus prints the home directory, leaving you where  you  were  (printing
       this after the home directory), while

	   cd; pwd

       leaves  you  in	the  home  directory.  Parenthesized commands are most
       often used to prevent cd from affecting the current shell.

       When a command to be executed is found not to be a builtin command  the
       shell  attempts to execute the command via execve(2).  Each word in the
       variable path names a directory in which the shell will	look  for  the
       command.  If it is given neither a -c nor a -t option, the shell hashes
       the names in these directories into an internal table so that  it  will
       try  an execve(2) in only a directory where 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 unhash), if the shell was given a -c
       or  -t  argument  or  in  any case for each directory component of path
       which does not begin with a `/', the  shell  concatenates  the  current
       working	directory with the given command name to form a path name of a
       file which it then attempts to execute.

       If the file has execute permissions but is not  an  executable  to  the
       system  (i.e.,  it  is  neither	an executable binary nor a script that
       specifies its interpreter), then it is assumed to be a file  containing
       shell  commands	and a new shell is spawned to read it.	The shell spe-
       cial alias may be set to specify an interpreter other  than  the  shell
       itself.

       On  systems which do not understand the `#!' script interpreter conven-
       tion the shell may be compiled to emulate it;  see  the	version  shell
       variable.  If so, the shell checks the first line of the file to see if
       it is of the form `#!interpreter arg ...'.  If it is, the shell	starts
       interpreter  with  the  given args and feeds the file to it on standard
       input.

   Input/output
       The standard input and standard output of a command may	be  redirected
       with the following syntax:

	       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 stan-
	       dard input.
       > name
       >! name
       >& name
       >&! name
	       The file name is used as standard output.  If the file does not
	       exist  then it is created; if the file exists, it is truncated,
	       its previous contents being lost.

	       If the shell variable noclobber 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  acciden-
	       tal  destruction  of  files.  In this case the `!' forms can be
	       used to suppress this check.

	       The forms involving `&' route the diagnostic  output  into  the
	       specified  file	as  well  as  the  standard  output.   name is
	       expanded in the same way as `<' input filenames are.
       >> name
       >>& name
       >>! name
       >>&! name
	       Like `>', but appends output to the end of name.  If the  shell
	       variable noclobber is set, then it is an error for the file not
	       to exist, unless one of the `!' forms is given.

       A command receives the environment in which the shell  was  invoked  as
       modified 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 command scripts to function as components of pipelines and allows
       the  shell  to  block  read  its input.	Note that the default standard
       input for a command run detached is not the empty file  /dev/null,  but
       the original standard input of the shell.  If this is a terminal and if
       the process attempts to read from the terminal, then the  process  will
       block and the user will be notified (see Jobs).

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

       The shell cannot presently  redirect  diagnostic  output  without  also
       redirecting  standard  output,  but  `(command > output-file) >& error-
       file' is often an acceptable workaround.  Either output-file or	error-
       file may be `/dev/tty' to send output to the terminal.

   Features
       Having  described  how  the  shell accepts, parses and executes command
       lines, we now turn to a variety of its useful features.

   Control flow
       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
       If the shell's input is not seekable, the shell buffers up input  when-
       ever a loop is being read and performs seeks in this internal buffer to
       accomplish the rereading implied by the loop.  (To the extent that this
       allows, backward gotos will succeed on non-seekable inputs.)

   Expressions
       The  if,  while and exit builtin commands use expressions with a common
       syntax.	The expressions can include any of the operators described  in
       the  next  three  sections.  Note that the @ builtin command (q.v.) has
       its own separate syntax.

   Logical, arithmetical and comparison operators
       These operators are similar to those of C and have the same precedence.
       They include

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

       Here  the  precedence  increases to the right, `==' `!=' `=~' and `!~',
       `<=' `>=' `<' and `>', `<<' and `>>', `+' and  `-',  `*'  `/'  and  `%'
       being, in groups, at the same level.  The `==' `!=' `=~' and `!~' oper-
       ators compare their arguments as strings; all others  operate  on  num-
       bers.   The  operators `=~' and `!~' are like `!=' and `==' except that
       the right hand side  is	a  glob-pattern  (see  Filename  substitution)
       against	which the left hand operand is matched.  This reduces the need
       for use of the switch builtin command in shell scripts when all that is
       really needed is pattern matching.

       Strings	which  begin  with  `0' are considered octal numbers.  Null or
       missing arguments are considered `0'.  The results 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 syntacti-
       cally significant to the parser (`&' `|' `<' `>' `(' `)')  they	should
       be surrounded by spaces.

   Command exit status
       Commands  can be executed in expressions and their exit status returned
       by enclosing them in braces (`{}').  Remember that the braces should be
       separated  from the words of the command by spaces.  Command executions
       succeed, returning true, i.e., `1', if the command exits with status 0,
       otherwise they fail, returning false, i.e., `0'.  If more detailed sta-
       tus information is required then the command should be executed outside
       of an expression and the status shell variable examined.

   File inquiry operators
       Some  of  these operators perform true/false tests on files and related
       objects.  They are of the form -op file, where op is one of

	   r   Read access
	   w   Write access
	   x   Execute access
	   X   Executable in the path or shell builtin, e.g., `-X ls' and  `-X
	       ls-F' are generally true, but `-X /bin/ls' is not (+)
	   e   Existence
	   o   Ownership
	   z   Zero size
	   s   Non-zero size (+)
	   g   Set-group-ID bit is set (+)
	   k   Sticky bit is set (+)
	   t   file  (which  must be a digit) is an open file descriptor for a
	       terminal device (+)
	   R   Has been migrated (convex only) (+)
	   L   Applies subsequent operators in a multiple-operator test  to  a
	       symbolic  link rather than to the file to which the link points
	       (+) *

       file is command and filename expanded and then tested to see if it  has
       the specified relationship to the real user.  If file does not exist or
       is inaccessible or, for the operators indicated by `*', if  the	speci-
       fied file type does not exist on the current system, then all enquiries
       return false, i.e., `0'.

       These operators may be combined for conciseness: `-xy file' is  equiva-
       lent  to `-x file && -y file'.  (+) For example, `-fx' is true (returns
       `1') for plain executable files, but not for directories.

       L may be used in a multiple-operator test to apply subsequent operators
       to  a  symbolic	link rather than to the file to which the link points.
       For example, `-lLo' is true for links owned by the invoking user.   Lr,
       Lw  and	Lx are always true for links and false for non-links.  L has a
       different meaning when it is the last operator in  a  multiple-operator
       test; see below.

       It  is  possible  but  not useful, and sometimes misleading, to combine
       operators which expect file to be a file with operators which  do  not,
       (e.g., X and t).  Following L with a non-file operator can lead to par-
       ticularly strange results.

       Other operators return other information, i.e., not just  `0'  or  `1'.
       (+) They have the same format as before; op may be one of

	   A	   Last  file  access time, as the number of seconds since the
		   epoch
	   A:	   Like A, but in timestamp format, e.g., `Fri May 14 16:36:10
		   1993'
	   M	   Last file modification time
	   M:	   Like M, but in timestamp format
	   C	   Last inode modification time
	   C:	   Like C, but in timestamp format
	   D	   Device number
	   I	   Inode number
	   F	   Composite file identifier, in the form device:inode
	   L	   The name of the file pointed to by a symbolic link
	   N	   Number of (hard) links
	   P	   Permissions, in octal, without leading zero
	   P:	   Like P, with leading zero
	   Pmode   Equivalent  to  `-P file & mode', e.g., `-P22 file' returns
		   `22' if file is writable by group and  other,  `20'	if  by
		   group only, and `0' if by neither
	   Pmode:  Like Pmode:, with leading zero
	   U	   Numeric userid
	   U:	   Username, or the numeric userid if the username is unknown
	   G	   Numeric groupid
	   G:	   Groupname,  or  the	numeric  groupid  if  the groupname is
		   unknown
       If the shell is compiled with POSIX  defined  (see  the	version  shell
       variable), the result of a file inquiry is based on the permission bits
       of the file and not on the result of the access(2)  system  call.   For
       example, if one tests a file with -w whose permissions would ordinarily
       allow writing but which is on a file system mounted read-only, the test
       will succeed in a POSIX shell but fail in a non-POSIX shell.

       File  inquiry operators can also be evaluated with the filetest builtin
       command (q.v.) (+).

   Jobs
       The shell associates a job with each pipeline.  It  keeps  a  table  of
       current jobs, printed by the jobs command, and assigns them small inte-
       ger 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
       suspend	key  (usually  `^Z'), which sends a STOP signal to the current
       job.  The shell will then normally indicate that the job has been `Sus-
       pended'	and  print  another prompt.  If the listjobs shell variable is
       set, all jobs will be listed like the jobs builtin command;  if	it  is
       set  to `long' the listing will be in long format, like `jobs -l'.  You
       can then manipulate the state of the suspended job.  You can put it  in
       the  ``background''  with the bg command or run some other commands and
       eventually bring the job back into the ``foreground''  with  fg.   (See
       also  the  run-fg-editor  editor command.)  A `^Z' takes effect immedi-
       ately and is like an interrupt in that pending output and unread  input
       are  discarded  when  it is typed.  The wait builtin command causes the
       shell to wait for all background jobs to complete.

       The `^]' key sends a delayed suspend signal, which does not generate  a
       STOP signal until a program attempts to read(2) it, to the current job.
       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.  The `^Y' key
       performs this function in csh(1); in tcsh, `^Y' is an editing  command.
       (+)

       A  job  being  run in the background stops 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  pro-
       duce 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  fore-
       ground.	Similarly, saying `%1 &' resumes job 1 in the background, just
       like `bg %1'.  A job can also be named by an unambiguous prefix of  the
       string  typed  in to start it: `%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' to specify a
       job whose text contains string, if there is only one such job.
       on  some systems.  It is an artifact from a `new' implementation of the
       tty driver which allows generation of  interrupt  characters  from  the
       keyboard  to tell jobs to stop.	See stty(1) and the setty builtin com-
       mand for details on setting options in the new tty driver.

   Status reporting
       The 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 right before it prints a	prompt.   This
       is  done so that it does not otherwise disturb your work.  If, however,
       you set the shell variable notify, the shell will  notify  you  immedi-
       ately  of  changes of status in background jobs.  There is also a shell
       command notify which marks a single process so that its status  changes
       will  be  immediately  reported.   By  default notify marks the current
       process; simply 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  jobs  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.

   Automatic, periodic and timed events (+)
       There are various ways to run commands and take other actions automati-
       cally at various times in the ``life cycle'' of the  shell.   They  are
       summarized  here, and described in detail under the appropriate Builtin
       commands, Special shell variables and Special aliases.

       The sched builtin command puts commands in a scheduled-event  list,  to
       be executed by the shell at a given time.

       The  beepcmd,  cwdcmd,  periodic,  precmd,  postcmd, and jobcmd Special
       aliases can be set, respectively, to execute commands  when  the  shell
       wants  to ring the bell, when the working directory changes, every tpe-
       riod minutes, before each prompt, before each  command  gets  executed,
       after  each  command  gets  executed,  and  when a job is started or is
       brought into the foreground.

       The autologout shell variable can be set to log out or lock  the  shell
       after a given number of minutes of inactivity.

       The  mail shell variable can be set to check for new mail periodically.

       The printexitvalue shell variable can be set to print the  exit	status
       of commands which exit with a status other than zero.

       The  rmstar  shell  variable can be set to ask the user, when `rm *' is
       typed, if that is really what was meant.

       The time shell variable can be set to execute the time builtin  command
       after the completion of any process that takes more than a given number
       of CPU seconds.

       The watch and who shell variables can be set to	report	when  selected
       users log in or out, and the log builtin command reports on those users
       at any time.

       respects.

       When  using  the  system's  NLS, the setlocale(3) function is called to
       determine appropriate character classification and sorting.  This func-
       tion  typically	examines  the LANG and LC_CTYPE environment variables;
       refer to the system documentation for further details.  When not  using
       the  system's  NLS,  the  shell	simulates  it by assuming that the ISO
       8859-1 character set is used whenever either of the LANG  and  LC_CTYPE
       variables are set, regardless of their values.  Sorting is not affected
       for the simulated NLS.

       In addition, with both real and simulated NLS, all printable characters
       in  the	range  \200-\377,  i.e.,  those that have M-char bindings, are
       automatically rebound to self-insert-command.  The corresponding  bind-
       ing for the escape-char sequence, if any, is left alone.  These charac-
       ters are not rebound if the NOREBIND environment variable is set.  This
       may  be	useful	for  the  simulated  NLS or a primitive real NLS which
       assumes full ISO 8859-1.  Otherwise, all M-char bindings in  the  range
       \240-\377  are  effectively  undone.  Explicitly rebinding the relevant
       keys with bindkey is of course still possible.

       Unknown characters (i.e., those that are neither printable nor  control
       characters) are printed in the format \nnn.  If the tty is not in 8 bit
       mode, other 8 bit characters are printed by converting  them  to  ASCII
       and  using  standout mode.  The shell never changes the 7/8 bit mode of
       the tty and tracks user-initiated changes of 7/8 bit mode.   NLS  users
       (or,  for  that	matter,  those who want to use a meta key) may need to
       explicitly set the tty in 8 bit mode through  the  appropriate  stty(1)
       command in, e.g., the ~/.login file.

   OS variant support (+)
       A  number  of  new builtin commands are provided to support features in
       particular operating systems.  All  are	described  in  detail  in  the
       Builtin commands section.

       On  systems  that  support  TCF	(aix-ibm370,  aix-ps2),  getspath  and
       setspath get and set the system execution path, getxvers  and  setxvers
       get  and  set the experimental version prefix and migrate migrates pro-
       cesses between sites.  The jobs builtin prints the site on  which  each
       job is executing.

       Under  BS2000,  bs2cmd  executes  commands of the underlying BS2000/OSD
       operating system.

       Under Domain/OS, inlib adds shared libraries to	the  current  environ-
       ment, rootnode changes the rootnode and ver changes the systype.

       Under Mach, setpath is equivalent to Mach's setpath(1).

       Under Masscomp/RTU and Harris CX/UX, universe sets the universe.

       Under  Harris CX/UX, ucb or att runs a command under the specified uni-
       verse.

       Under Convex/OS, warp prints or sets the universe.

       The VENDOR, OSTYPE and MACHTYPE environment variables indicate  respec-
       tively  the  vendor,  operating system and machine type (microprocessor

       The  version shell variable indicates what options were chosen when the
       shell was compiled.

       Note also the newgrp builtin, the afsuser and  echo_style  shell  vari-
       ables  and  the	system-dependent  locations of the shell's input files
       (see FILES).

   Signal handling
       Login shells ignore interrupts when reading the	file  ~/.logout.   The
       shell  ignores quit signals unless started with -q.  Login shells catch
       the terminate signal, but non-login shells inherit the terminate behav-
       ior  from their parents.  Other signals have the values which the shell
       inherited from its parent.

       In shell scripts, the shell's handling of interrupt and terminate  sig-
       nals  can be controlled with onintr, and its handling of hangups can be
       controlled with hup and nohup.

       The shell exits on a hangup (see also the logout shell  variable).   By
       default,  the shell's children do too, but the shell does not send them
       a hangup when it exits.	hup arranges for the shell to send a hangup to
       a child when it exits, and nohup sets a child to ignore hangups.

   Terminal management (+)
       The  shell  uses  three	different  sets  of  terminal (``tty'') modes:
       `edit', used when editing, `quote', used when quoting  literal  charac-
       ters,  and  `execute',  used  when executing commands.  The shell holds
       some settings in each mode constant, so commands which leave the tty in
       a  confused  state  do  not  interfere  with the shell.	The shell also
       matches changes in the speed and padding of the tty.  The list  of  tty
       modes  that  are  kept  constant  can be examined and modified with the
       setty builtin.  Note that although the editor uses CBREAK mode (or  its
       equivalent), it takes typed-ahead characters anyway.

       The  echotc,  settc  and  telltc commands can be used to manipulate and
       debug terminal capabilities from the command line.

       On systems that support SIGWINCH or SIGWINDOW, the shell adapts to win-
       dow  resizing automatically and adjusts the environment variables LINES
       and COLUMNS if set.  If the environment variable TERMCAP  contains  li#
       and  co# fields, the shell adjusts them to reflect the new window size.

REFERENCE

       The next sections of this manual describe all of the available  Builtin
       commands, Special aliases and Special shell variables.

   Builtin commands
       %job    A synonym for the fg builtin command.

       %job &  A synonym for the bg builtin command.

       :       Does nothing, successfully.

       @
       @ name = expr
       @ name[index] = expr
       @ name++|--
	       expr  contains  `<',  `>', `&' or `' then at least that part of
	       expr must be placed within `()'.  Note that the syntax of  expr
	       has nothing to do with that described under Expressions.

	       The fourth and fifth forms increment (`++') or decrement (`--')
	       name or its index'th component.

	       The space between `@' and name is required.  The spaces between
	       name and `=' and between `=' and expr are optional.  Components
	       of expr must be separated by spaces.

       alias [name [wordlist]]
	       Without arguments, prints all aliases.  With name,  prints  the
	       alias  for  name.   With name and wordlist, assigns wordlist as
	       the alias of name.  wordlist is command	and  filename  substi-
	       tuted.	name  may  not	be `alias' or `unalias'.  See also the
	       unalias builtin command.

       alloc   Shows the amount of dynamic memory acquired, broken  down  into
	       used  and  free	memory.   With an argument shows the number 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, because systems  other  than  the
	       VAX may use a different memory allocator.

       bg [%job ...]
	       Puts  the  specified  jobs  (or, without arguments, the current
	       job) into the background, continuing each  if  it  is  stopped.
	       job may be a number, a string, `', `%', `+' or `-' as described
	       under Jobs.

       bindkey [-l|-d|-e|-v|-u] (+)
       bindkey [-a] [-b] [-k] [-r] [--] key (+)
       bindkey [-a] [-b] [-k] [-c|-s] [--] key command (+)
	       Without options, the first form lists all bound	keys  and  the
	       editor  command	to  which each is bound, the second form lists
	       the editor command to which key is bound  and  the  third  form
	       binds the editor command command to key.  Options include:

	       -l  Lists  all editor commands and a short description of each.
	       -d  Binds all keys to the standard  bindings  for  the  default
		   editor.
	       -e  Binds all keys to the standard GNU Emacs-like bindings.
	       -v  Binds all keys to the standard vi(1)-like bindings.
	       -a  Lists  or  changes key-bindings in the alternative key map.
		   This is the key map used in vi command mode.
	       -b  key is interpreted as a control character written  ^charac-
		   ter (e.g., `^A') or C-character (e.g., `C-A'), a meta char-
		   acter written M-character (e.g.,  `M-A'),  a  function  key
		   written  F-string (e.g., `F-string'), or an extended prefix
		   key written X-character (e.g., `X-A').
	       -k  key is interpreted as a symbolic arrow key name, which  may
		   be one of `down', `up', `left' or `right'.
	       -r  Removes  key's  binding.  Be careful: `bindkey -r' does not
		   bind key to self-insert-command (q.v.), it unbinds key com-
		   pletely.
	       -c  command  is	interpreted  as  a builtin or external command
		   instead of an editor command.

	       key may be a single character or a string.   If	a  command  is
	       bound  to  a string, the first character of the string is bound
	       to sequence-lead-in and the entire string is bound to the  com-
	       mand.

	       Control	characters in key can be literal (they can be typed by
	       preceding them with the editor command quoted-insert,  normally
	       bound  to  `^V')  or written caret-character style, e.g., `^A'.
	       Delete is written `^?'  (caret-question mark).  key and command
	       can  contain backslashed escape sequences (in the style of Sys-
	       tem V echo(1)) as follows:

		   \a	   Bell
		   \b	   Backspace
		   \e	   Escape
		   \f	   Form feed
		   \n	   Newline
		   \r	   Carriage return
		   \t	   Horizontal tab
		   \v	   Vertical tab
		   \nnn    The ASCII character corresponding to the octal num-
			   ber nnn

	       `\'  nullifies  the special meaning of the following character,
	       if it has any, notably `\' and `^'.

       bs2cmd bs2000-command (+)
	       Passes bs2000-command to the  BS2000  command  interpreter  for
	       execution.  Only  non-interactive commands can be executed, and
	       it is not possible to execute any command  that	would  overlay
	       the image of the current process, like /EXECUTE or /CALL-PROCE-
	       DURE. (BS2000 only)

       break   Causes execution to resume after the end of the nearest enclos-
	       ing  foreach  or  while.  The remaining commands on the current
	       line are executed.  Multi-level breaks  are  thus  possible  by
	       writing them all on one line.

       breaksw Causes a break from a switch, resuming after the endsw.

       builtins (+)
	       Prints the names of all builtin commands.

       bye (+) A  synonym  for	the logout builtin command.  Available only if
	       the shell was so compiled; see the version shell variable.

       case label:
	       A label in a switch statement as discussed below.

       cd [-p] [-l] [-n|-v] [name]
	       If a directory name  is	given,	changes  the  shell's  working
	       directory to name.  If not, changes to home.  If name is `-' it
	       is interpreted as the previous  working	directory  (see  Other
	       substitutions).	 (+) If name is not a subdirectory of the cur-
	       rent directory (and does not begin with `/',  `./'  or  `../'),
	       each  component	of the variable cdpath is checked to see if it
	       has a subdirectory name.  Finally, if all else fails  but  name

       chdir   A synonym for the cd builtin command.

       complete [command [word/pattern/list[:select]/[[suffix]/] ...]] (+)
	       Without arguments, lists all completions.  With command,  lists
	       completions  for  command.  With command and word etc., defines
	       completions.

	       command may be a full command name or a glob-pattern (see File-
	       name  substitution).   It  can  begin with `-' to indicate that
	       completion should be used only when command is ambiguous.

	       word specifies which word relative to the current word is to be
	       completed, and may be one of the following:

		   c   Current-word  completion.   pattern  is	a glob-pattern
		       which must match the beginning of the current  word  on
		       the  command  line.  pattern is ignored when completing
		       the current word.
		   C   Like c, but includes pattern when completing  the  cur-
		       rent word.
		   n   Next-word  completion.  pattern is a glob-pattern which
		       must match the beginning of the previous  word  on  the
		       command line.
		   N   Like  n,  but  must match the beginning of the word two
		       before the current word.
		   p   Position-dependent completion.  pattern	is  a  numeric
		       range,  with  the same syntax used to index shell vari-
		       ables, which must include the current word.

	       list, the list of possible completions, may be one of the  fol-
	       lowing:

		   a	   Aliases
		   b	   Bindings (editor commands)
		   c	   Commands (builtin or external commands)
		   C	   External  commands  which  begin  with the supplied
			   path prefix
		   d	   Directories
		   D	   Directories which begin with the supplied path pre-
			   fix
		   e	   Environment variables
		   f	   Filenames
		   F	   Filenames which begin with the supplied path prefix
		   g	   Groupnames
		   j	   Jobs
		   l	   Limits
		   n	   Nothing
		   s	   Shell variables
		   S	   Signals
		   t	   Plain (``text'') files
		   T	   Plain (``text'') files which begin  with  the  sup-
			   plied path prefix
		   v	   Any variables
		   u	   Usernames
		   x	   Like  n,  but  prints  select  when list-choices is
			   used.
		   X	   Completions
	       message when the list-choices editor command is used.

	       suffix is a single character to be  appended  to  a  successful
	       completion.  If null, no character is appended.	If omitted (in
	       which case the fourth delimiter can also be omitted),  a  slash
	       is appended to directories and a space to other words.

	       Now  for some examples.	Some commands take only directories as
	       arguments, so there's no point completing plain files.

		   > complete cd 'p/1/d/'

	       completes only the first word following	`cd'  (`p/1')  with  a
	       directory.   p-type  completion can also be used to narrow down
	       command completion:

		   > co[^D]
		   complete compress
		   > complete -co* 'p/0/(compress)/'
		   > co[^D]
		   > compress

	       This completion completes commands (words in position 0, `p/0')
	       which  begin with `co' (thus matching `co*') to `compress' (the
	       only word in the list).	The leading `-'  indicates  that  this
	       completion is to be used with only ambiguous commands.

		   > complete find 'n/-user/u/'

	       is  an example of n-type completion.  Any word following `find'
	       and immediately following `-user' is completed from the list of
	       users.

		   > complete cc 'c/-I/d/'

	       demonstrates  c-type  completion.   Any word following `cc' and
	       beginning with `-I' is completed as a directory.  `-I'  is  not
	       taken as part of the directory because we used lowercase c.

	       Different lists are useful with different commands.

		   > complete alias 'p/1/a/'
		   > complete man 'p/*/c/'
		   > complete set 'p/1/s/'
		   > complete true 'p/1/x:Truth has no options./'

	       These complete words following `alias' with aliases, `man' with
	       commands, and `set' with shell variables.  `true' doesn't  have
	       any options, so x does nothing when completion is attempted and
	       prints `Truth has no  options.'	when  completion  choices  are
	       listed.

	       Note  that  the	man example, and several other examples below,
	       could just as well have used 'c/*' or 'n/*' as 'p/*'.

	       Words can be completed from a variable evaluated at  completion
	       time,

		   rtfm.mit.edu tesla.ee.cornell.edu uunet.uu.net

	       or from a command run at completion time:

		   > complete kill 'p/*/`ps | awk \{print\ \$1\}`/'
		   > kill -9 [^D]
		   23113 23377 23380 23406 23429 23529 23530 PID

	       Note that the complete command does not itself quote its  argu-
	       ments,  so  the	braces,  space and `$' in `{print $1}' must be
	       quoted explicitly.

	       One command can have multiple completions:

		   > complete dbx 'p/2/(core)/' 'p/*/c/'

	       completes the second argument to `dbx' with the word `core' and
	       all  other  arguments  with commands.  Note that the positional
	       completion  is  specified  before  the  next-word   completion.
	       Because	completions  are  evaluated from left to right, if the
	       next-word completion were specified first it would always match
	       and the positional completion would never be executed.  This is
	       a common mistake when defining a completion.

	       The select pattern is useful when a command  takes  files  with
	       only particular forms as arguments.  For example,

		   > complete cc 'p/*/f:*.[cao]/'

	       completes `cc' arguments to files ending in only `.c', `.a', or
	       `.o'.  select can also exclude files, using negation of a glob-
	       pattern	as  described  under Filename substitution.  One might
	       use

		   > complete rm 'p/*/f:^*.{c,h,cc,C,tex,1,man,l,y}/'

	       to exclude precious  source  code  from	`rm'  completion.   Of
	       course,	one  could still type excluded names manually or over-
	       ride the completion mechanism using  the  complete-word-raw  or
	       list-choices-raw editor commands (q.v.).

	       The  `C', `D', `F' and `T' lists are like `c', `d', `f' and `t'
	       respectively, but they use the select argument in  a  different
	       way:  to restrict completion to files beginning with a particu-
	       lar path prefix.  For example, the Elm mail program uses `=' as
	       an abbreviation for one's mail directory.  One might use

		   > complete elm c@=@F:$HOME/Mail/@

	       to  complete  `elm  -f =' as if it were `elm -f ~/Mail/'.  Note
	       that we used `@' instead of `/' to  avoid  confusion  with  the
	       select  argument,  and  we  used `$HOME' instead of `~' because
	       home directory substitution works at only the  beginning  of  a
	       word.

	       suffix  is  used  to add a nonstandard suffix (not space or `/'
	       for directories