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CSH(1)			  BSD General Commands Manual			CSH(1)

NAME
     csh -- a shell (command interpreter) with C-like syntax

SYNOPSIS
     csh [-bcefimnstVvXx] [argument ...]
     csh [-l]

DESCRIPTION
     csh is a command language interpreter incorporating a history mechanism
     (see History substitutions), job control facilities (see Jobs), interac-
     tive file name and	user name completion (see File name completion), and a
     C-like syntax.  It	is used	both as	an interactive login shell and a shell
     script command processor.

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

     The rest of the flag arguments are	interpreted as follows:

     -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	    Commands are read from the (single)	following argument which must
	    be present.	 Any remaining arguments are placed in argv.

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

     -f	    The	shell will start faster, because it will neither search	for
	    nor	execute	commands from the file .cshrc in the invoker's home
	    directory.	Note: if the environment variable HOME is not set,
	    fast startup is the	default.

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

     -l	    The	shell is a login shell (only applicable	if -l is the only flag
	    specified).

     -m	    Read .cshrc, regardless of its owner and group.  This option is
	    dangerous and should only be used by su(1).

     -n	    Commands are parsed, but not executed.  This aids in syntactic
	    checking of	shell scripts.	When used interactively, the shell can
	    be terminated by pressing control-D	(end-of-file character), since
	    exit will not work.

     -s	    Command input is taken from	the standard input.

     -t	    A single line of input is read and executed.  A backslash (`\')
	    may	be used	to escape the newline at the end of this line and con-
	    tinue onto another line.

     -V	    Causes the verbose variable	to be set even before .cshrc is	exe-
	    cuted.

     -v	    Causes the verbose variable	to be set, with	the effect that	com-
	    mand input is echoed after history substitution.

     -X	    Causes the echo variable to	be set even before .cshrc is executed.

     -x	    Causes the echo variable to	be set,	so that	commands are echoed
	    immediately	before execution.

     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	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 hash mark
     (`#'); i.e., if the script	does not start with a comment.	Remaining ar-
     guments initialize	the variable argv.

     An	instance of csh	begins by executing commands from the file
     /etc/csh.cshrc and, if this is a login shell, /etc/csh.login.  It then
     executes commands from .cshrc in the home directory of the	invoker, and,
     if	this is	a login	shell, the file	.login in the same location.  It is
     typical for users on CRTs to put the command stty crt in their .login
     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
     later.

     The shell repeatedly performs the following actions: a line of command
     input is read and broken into "words".  This sequence of words is placed
     on	the command history list and parsed.  Finally each command in the cur-
     rent line is executed.

     When a login shell	terminates it executes commands	from the files .logout
     in	the user's home	directory and /etc/csh.logout.

   Lexical structure
     The shell splits input lines into words at	blanks and tabs	with the fol-
     lowing exceptions.	 The characters	`&', `|', `;', `<', `>', `(', and `)'
     form separate words.  If doubled in `&&', `||', `<<', or `>>', these
     pairs form	single words.  These parser metacharacters may be made part of
     other words, or have their	special	meaning	prevented, by preceding	them
     with a backslash (`\').  A	newline	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 later.  Within pairs of `'' or `"' characters, a	newline	pre-
     ceded by a	`\' gives a true newline character.

     When the shell's input is not a terminal, the character `#' introduces a
     comment that continues to the end of the input line.  This	special	mean-
     ing is prevented when preceded by `\' and in quotations using ``',	`'',
     and `"'.

   Commands
     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 a `&'.

     Any of the	above may be placed in `(' `)' to form a simple	command	(that
     may be a component	of a pipeline, for example).  It is also possible to
     separate pipelines	with `||' or `&&' showing, as in the C language, that
     the second	is to be executed only if the first fails or succeeds, respec-
     tively.  (See Expressions.)

   Jobs
     The shell associates a job	with each pipeline.  It	keeps a	table of cur-
     rent jobs,	printed	by the jobs command, and assigns them small integer
     numbers.  When a job is started asynchronously with `&', the shell	prints
     a line that looks like:

	   [1] 1234

     showing 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	^Z
     (control-Z), which	sends a	SIGSTOP	signal to the current job.  The	shell
     will then normally	show that the job has been "Stopped", and print	an-
     other prompt.  You	can then manipulate the	state of this job, putting it
     in	the background with the	bg command, or run some	other commands and
     eventually	bring the job back into	the foreground with the	fg command.  A
     ^Z	takes effect immediately and is	like an	interrupt in that pending out-
     put and unread input are discarded	when it	is typed.  There is another
     special key ^Y that does not generate a SIGSTOP signal until a program
     attempts to read(2) it.  This request can usefully	be typed ahead when
     you have prepared some commands for a job that 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 out-
     put 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 number 1 back	into the foreground.
     Similarly,	saying %1 & resumes job	number 1 in the	background.  Jobs can
     also be named by prefixes of the string typed in to start them, if	these
     prefixes 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 string, if there is only one such job.

     The shell maintains a notion of the current and previous jobs.  In	output
     about 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
     history mechanism (described below), `%%' is also a synonym for the cur-
     rent job.

     The job control mechanism requires	that the stty(1) option	new be set.
     It	is an artifact from a new implementation of the	tty driver that	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.

   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 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 notify, the	shell will notify you immediately of
     changes of	status in background jobs.  There is also a shell command
     notify that marks a single	process	so that	its status changes will	be im-
     mediately 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 try	to exit	again immediately, the shell will not
     warn you a	second time, and the suspended jobs will be terminated.

   File	name completion
     When the file name	completion feature is enabled by setting the shell
     variable filec (see set), csh 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 ex-
     ample, 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>

     csh will complete the prefix "ch" to the only matching file name
     "chaosnet", changing the input line to

	   % vi	chaosnet

     However, given

	   % vi	D<escape>

     csh 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, csh 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
     tilde 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 nobeep.

     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 fignore to the list of suffixes to be	ig-
     nored.  Thus, if fignore 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, fignore does not affect the listing of file names by
     control-D.	 All files are listed regardless of their suffixes.

   Substitutions
     We	now describe the various transformations the shell performs on the in-
     put in the	order in which they occur.

   History substitutions
     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 anywhere
     in	the input stream (with the proviso that	they do	not nest).  This `!'
     may be preceded by	a `\' to prevent its special meaning; for convenience,
     a `!' character 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.)  Any input	line that contains history substitution	is echoed on
     the terminal before it is executed	as it would have been typed without
     history substitution.

     Commands input from the terminal that 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 the history list is controlled by the history variable; the pre-
     vious command is always retained, regardless of the value of the history
     variable.	Commands are numbered sequentially from	1.

     For definiteness, consider	the following output from the history command:

	   09  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 prompt	by placing a `!' 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 change, simply reintroduce the
     words of the specified events, each separated by a	single blank.  As a
     special case, `!!'	refers to the previous command;	thus `!!' alone	is a
     redo.

     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? 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, a sequence of modifiers can be
     placed, 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 once on each word, prefixing the above;
		   e.g., `g&'.
	   a	   Apply the change as many times as possible on a single
		   word, prefixing the above.  It can be used together with
		   `g' to apply	a substitution globally.
	   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 new-
		   lines.

     Unless preceded by	a `g' the change is applied only to the	first modifi-
     able word.	 With substitutions, it	is an error for	no word	to be applica-
     ble.

     The left-hand side	of substitutions are not regular expressions in	the
     sense of the editors, but instead 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 `\'	also quotes `&'.  A NULL l (`//') uses the
     previous string either from an 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.,
     `!$'.  Here, the reference	is to the previous command unless a previous
     history reference occurred	on the same line in which case this form re-
     peats the previous	reference.  Thus "!?foo?^ !$" 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 previous
     command.  Finally,	a history substitution may be surrounded with `{' and
     `}' if necessary to insulate it from the characters that follow.  Thus,
     after ls -ld ~paul	we might do !{l}a to do	ls -ld ~paula, while !la would
     look for a	command	starting with "la".

   Quotations with ' and "
     The quotation of strings by `'' and `"' can be used to prevent all	or
     some of the remaining substitutions.  Strings enclosed in `'' are pre-
     vented from any further interpretation.  Strings enclosed in `"' may be
     expanded as described below.

     In	both cases the resulting text becomes (all or part of) a single	word;
     only in one special case (see Command Substitution	below) does a `"'
     quoted string yield parts of more than one	word; `'' quoted strings never
     do.

   Alias substitution
     The shell maintains a list	of aliases that	can be established, displayed
     and modified by the alias and unalias 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 that is the alias for that command is reread with the
     history mechanism available as though that	command	were the previous in-
     put 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 that pr's its
     arguments to the line printer.

   Variable substitution
     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 argv	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 set and
     unset 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	verbose	variable is a toggle that
     causes command input to be	echoed.	 The setting of	this variable results
     from the -v command-line option.

     Other operations treat variables numerically.  The	@ command permits nu-
     meric calculations	to be performed	and the	result assigned	to a variable.
     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 additional 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 double quotes (`"'), where it always occurs, and within single
     quotes (`''), where it never occurs.  Strings quoted by backticks (` `)
     are interpreted later (see	Command	substitution below), so	`$' substitu-
     tion does not occur there until later, if at all.	A `$' is passed	un-
     changed 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 argu-
     ments.

     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 sep-
     arated by blanks.	When the `:q' modifier is applied to a substitution
     the variable 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 that is not set.

	   $name
	   ${name}
		   Are replaced	by the words of	the value of variable name,
		   each	separated by a blank.  Braces insulate name from fol-
		   lowing characters that 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 name	is not a shell vari-
		   able, but is	set in the environment,	then that value	is re-
		   turned (but `:' modifiers and the other forms given below
		   are not available here).
	   $name[selector]
	   ${name[selector]}
		   May be used to select only some of the words	from the value
		   of name.  The selector is subjected to `$' 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	number 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	`{'
     `}' appear	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.  Do NOT use this mechanism for generating temporary
		   file	names; see mktemp(1) instead.
	   $!	   Substitute the (decimal) process number of the last back-
		   ground process started by this shell.
	   $<	   Substitutes a line from the standard	input, with no further
		   interpretation.  It can be used to read from	the keyboard
		   in a	shell script.

   Command and filename	substitution
     The remaining substitutions, command and filename substitution, are ap-
     plied selectively to the arguments	of built-in commands.  By selectively,
     we	mean that portions of expressions which	are not	evaluated are not sub-
     jected to these expansions.  For commands that 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 shown by a	command	enclosed in ``'.  The output
     from such a command is normally broken into separate words	at blanks,
     tabs, and newlines, with null words being discarded; this text then re-
     places the	original string.  Within double	quotes (`"'), 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.

   Filename substitution
     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
     that match	the pattern.  In a list	of words specifying filename substitu-
     tion 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	character lex-
     ically between the	two (inclusive).  Within "[...]", the name of a
     character class enclosed in `[:' and `:]' stands for the list of all
     characters	belonging to that class.  Supported character classes:

	   alnum   cntrl   lower   space
	   alpha   digit   print   upper
	   blank   graph   punct   xdigit

     These match characters using the macros specified in isalnum(3),
     isalpha(3), and so	on.  A character class may not be used as an endpoint
     of	a range.

     The character `~' at the beginning	of a filename refers to	home directo-
     ries.  Standing alone, i.e., `~', it expands to the invoker's home	direc-
     tory as reflected in the value of the variable home.  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 does not appear 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" without 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 re-
     sults of the match	to "*box".)  As	a special case `{', `}', and `{}' are
     passed undisturbed.

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

	   < name  Open	file name (which is first variable, command, and file-
		   name	expanded) as the standard input.
	   << word
		   Read	the shell input	up to a	line that is identical to
		   word.  word is not subjected	to variable, command, or file-
		   name	substitution, and each input line is compared to word
		   before any substitutions are	done on	the input line.	 Un-
		   less	a quoting `\', `"', `''	or ``' appears in word,	vari-
		   able	and command substitution is performed on the interven-
		   ing lines, allowing `\' to quote `$', `\' and ``'.  Com-
		   mands that are substituted have all blanks, tabs, and new-
		   lines preserved, except for the final newline which is
		   dropped.  The resultant text	is placed in an	anonymous tem-
		   porary file that is given to	the command as its standard
		   input.
	   > name
	   >! name
	   >& name
	   >&! name
		   The file name is used as the	standard output.  If the file
		   does	not exist then it is created; if the file exists, it
		   is truncated; its previous contents are lost.

		   If the 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 acci-
		   dental destruction of files.	 Here, the `!' forms can be
		   used	to suppress this check.

		   The forms involving `&' route the standard error 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
		   Uses	file name as the standard output; like `>' but places
		   output at the end of	the file.  If the variable noclobber
		   is set, then	it is an error for the file not	to exist un-
		   less	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; in-
     stead 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 not modified to be the empty file /dev/null; instead
     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 Jobs
     above).

     The standard error	output may be directed through a pipe with the stan-
     dard output.  Simply use the form `|&' instead of just `|'.

   Expressions
     Several of	the built-in commands (to be described later) take expres-
     sions, in which the operators are similar to those	of C, with the same
     precedence, but with the opposite grouping: right to left.	 These expres-
     sions appear in the @, exit, if, and while	commands.  The following oper-
     ators are available:

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

     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
     pattern (containing, e.g.,	*'s, ?'s, and instances	of "[...]") against
     which the left-hand operand is matched.  This reduces the need for	use of
     the switch	statement in shell scripts when	all that is really needed is
     pattern matching.

     Strings that begin	with `0' are considered	octal numbers.	Null or	miss-
     ing 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	that are syntactically signif-
     icant to the parser (`&', `|', `<', `>', `(', and `)'), they should be
     surrounded	by spaces.

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

	   r	   read	access
	   w	   write access
	   x	   execute access
	   e	   existence
	   o	   ownership
	   z	   zero	size
	   f	   plain file
	   d	   directory
	   p	   named pipe (FIFO)
	   l	   symbolic link

     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	an expression and the variable status exam-
     ined.

   Control flow
     The shell contains	several	commands that can be used to regulate the flow
     of	control	in command files (shell	scripts) and (in limited but useful
     ways) from	terminal input.	 These commands	all operate by forcing the
     shell to reread or	skip in	its input and, because of the implementation,
     restrict the placement of some of the commands.

     The foreach, switch, and while statements,	as well	as the if-then-else
     form of the if 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.)

   Built-in commands
     Built-in commands are executed within the shell.  If a built-in command
     occurs as any component of	a pipeline except the last then	it is executed
     in	a sub-shell.

	   alias
	   alias name
	   alias name wordlist
		   The first form prints all aliases.  The second form prints
		   the alias for name.	The final form assigns the specified
		   wordlist as the alias of name; wordlist is command and
		   filename substituted.  name is not allowed to be "alias" or
		   "unalias".

	   bg
	   bg %job ...
		   Puts	the current or specified jobs into the background,
		   continuing them if they were	stopped.

	   break   Causes execution to resume after the	end of the nearest en-
		   closing 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.

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

	   cd
	   cd name
	   chdir
	   chdir name
		   Change the shell's working directory	to directory name.  If
		   no argument is given	then change to the home	directory of
		   the user.  If name is not found as a	subdirectory of	the
		   current directory (and does not begin with `/', `./'	or
		   `../'), then	each component of the variable cdpath is
		   checked to see if it	has a subdirectory name.  Finally, if
		   all else fails but name is a	shell variable whose value be-
		   gins	with `/', then this is tried to	see if it is a direc-
		   tory.

	   continue
		   Continue execution of the nearest enclosing while or
		   foreach.  The rest of the commands on the current line are
		   executed.

	   default:
		   Labels the default case in a	switch statement.  The default
		   should come after all case labels.

	   dirs	   Prints the directory	stack; the top of the stack is at the
		   left, the first directory in	the stack being	the current
		   directory.

	   echo	wordlist
	   echo	-n wordlist
		   The specified words are written to the shell's standard
		   output, separated by	spaces,	and terminated with a newline
		   unless the -n option	is specified.

	   else
	   end
	   endif
	   endsw   See the description of the foreach, if, switch, and while
		   statements below.

	   eval	arg ...
		   (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 eval.

	   exec	command
		   The specified command is executed in	place of the current
		   shell.

	   exit
	   exit	(expr)
		   The shell exits either with the value of the	status vari-
		   able	(first form) or	with the value of the specified	expr
		   (second form).

	   fg
	   fg %job ...
		   Brings the current or specified jobs	into the foreground,
		   continuing them if they were	stopped.

	   foreach name	(wordlist)
	   ...
	   end	   The variable	name is	successively set to each member	of
		   wordlist and	the sequence of	commands between this command
		   and the matching end	are executed.  (Both foreach and end
		   must	appear alone on	separate lines.)  The built-in command
		   continue may	be used	to continue the	loop prematurely and
		   the built-in	command	break to terminate it prematurely.
		   When	this command is	read from the terminal,	the loop is
		   read	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.

	   glob	wordlist
		   Like	echo but no `\'	escapes	are recognized and words are
		   delimited by	NUL characters in the output.  Useful for pro-
		   grams that wish to use the shell to filename	expand a list
		   of words.

	   goto	word
		   The specified word 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.

	   hashstat
		   Print a statistics line showing how effective the internal
		   hash	table has been at locating commands (and avoiding
		   exec's).  An	exec is	attempted for each component of	the
		   path	where the hash function	indicates a possible hit, and
		   in each component that does not begin with a	`/'.

	   history
	   history n
	   history -h n
	   history -r n
		   Displays the	history	event list; if n is given, only	the n
		   most	recent events are printed.  The	-h option causes the
		   history list	to be printed without leading numbers.	This
		   format produces files suitable for sourcing using the -h
		   option to source.  The -r option reverses the order of
		   printout to be most recent first instead of oldest first.

	   if (expr) command
		   If the specified expression evaluates to true, then the
		   single command with arguments is executed.  Variable	sub-
		   stitution on	command	happens	early, at the same time	it
		   does	for the	rest of	the if command.	 command must be a
		   simple command, not a pipeline, a command list, or a	paren-
		   thesized command list.  Input/output	redirection occurs
		   even	if expr	is false, i.e.,	when command is	not executed
		   (this is a bug).

	   if (expr) then
	   ...
	   else	if (expr2) then
	   ...
	   else
	   ...
	   endif   If the specified expr is true then the commands up to the
		   first else are executed; otherwise if expr2 is true then
		   the commands	up to the second else are executed, etc.  Any
		   number of else-if pairs are possible; only one endif	is
		   needed.  The	else part is likewise optional.	 (The words
		   else	and endif must appear at the beginning of input	lines;
		   the if must appear alone on its input line or after an
		   else.)

	   jobs
	   jobs	-l
		   Lists the active jobs; the -l option	lists process IDs in
		   addition to the normal information.

	   kill	%job
	   kill	   [-s signal_name] pid
	   kill	-sig pid ...
	   kill	-l [exit_status]
		   Sends either	the SIGTERM (terminate)	signal or the speci-
		   fied	signal to the specified	jobs or	processes.  Signals
		   are either given by number or by names (as given in
		   <signal.h>, stripped	of the prefix "SIG").  The signal
		   names are listed by "kill -l"; if an	exit_status is speci-
		   fied, only the corresponding	signal name will be written.
		   There is no default;	just saying "kill" does	not send a
		   signal to the current job.  If the signal being sent	is
		   SIGTERM (terminate) or SIGHUP (hangup), then	the job	or
		   process will	be sent	a SIGCONT (continue) signal as well.

	   limit
	   limit resource
	   limit resource maximum-use
	   limit -h
	   limit -h resource
	   limit -h resource maximum-use
		   Limits the consumption by the current process and each
		   process it creates to not individually exceed maximum-use
		   on the specified resource.  If no maximum-use is given,
		   then	the current limit is printed; if no resource is	given,
		   then	all limitations	are given.  If the -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 cur-
		   rent	limits.	 Only the superuser may	raise the hard limits,
		   but a user may lower	or raise the current limits within the
		   legal range.

		   Resources controllable currently include:

		   cputime	 the maximum number of CPU-seconds to be used
				 by each process.

		   filesize	 the largest single file (in bytes) that can
				 be created.

		   datasize	 the maximum growth (in	bytes) of the data
				 segment.

		   stacksize	 the maximum size of the automatically-ex-
				 tended	stack region.

		   coredumpsize	 the size of the largest core dump (in bytes)
				 that will be created.

		   memoryuse	 the maximum size (in bytes) to	which a
				 process's resident set	size (RSS) may grow.
				 Not enforced.

		   memorylocked	 The maximum size (in bytes) which a process
				 may lock into memory using the	mlock(2) func-
				 tion.

		   maxproc	 The maximum number of simultaneous processes
				 for this user ID.

		   openfiles	 The maximum number of simultaneous open files
				 for this user ID.

		   vmemoryuse	 the maximum size (in bytes) to	which a
				 process's total size may grow.

		   The maximum-use may be given	as a (floating point or	inte-
		   ger)	number followed	by a scale factor.  For	all limits
		   other than cputime the default scale	is `k' or "kilobytes"
		   (1024 bytes); a scale factor	of `m' or "megabytes" may also
		   be used.  For cputime the default scale is "seconds"; a
		   scale factor	of `m' for minutes or `h' for hours, or	a time
		   of the form "mm:ss" giving minutes and seconds also may be
		   used.

		   For both resource names and scale factors, unambiguous pre-
		   fixes of the	names suffice.

	   login   Terminate a login shell, replacing it with an instance of
		   /usr/bin/login.  This is one	way to log off,	included for
		   compatibility with sh(1).

	   logout  Terminate a login shell.  Especially	useful if ignoreeof is
		   set.

	   nice
	   nice	+number
	   nice	command
	   nice	+number	command
		   The first form sets the scheduling priority for this	shell
		   to 4.  The second form sets the priority to the given
		   number.  The	final two forms	run command at priority	4 and
		   number respectively.	 The greater the number, the less CPU
		   the process will get.  The superuser	may specify negative
		   priority by using "nice -number ...".  command is always
		   executed in a sub-shell, and	the restrictions placed	on
		   commands in simple if statements apply.

	   nohup
	   nohup command
		   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 nohup'ed.

	   notify
	   notify %job ...
		   Causes the shell to notify the user asynchronously when the
		   status of the current or specified jobs change; normally
		   notification	is presented before a prompt.  This is auto-
		   matic if the	shell variable notify is set.

	   onintr
	   onintr -
	   onintr label
		   Control the action of the shell on interrupts.  The first
		   form	restores the default action of the shell on inter-
		   rupts, 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 re-
		   ceived or a child process terminates	because	it was inter-
		   rupted.

		   In any case,	if the shell is	running	detached and inter-
		   rupts are being ignored, all	forms of onintr	have no	mean-
		   ing and interrupts continue to be ignored by	the shell and
		   all invoked commands.  Finally, onintr statements are ig-
		   nored in the	system startup files where interrupts are dis-
		   abled (/etc/csh.cshrc, /etc/csh.login).

	   popd
	   popd	+n
		   Pops	the directory stack, returning to the new top direc-
		   tory.  With an argument "+n"	discards the n'th entry	in the
		   stack.  The members of the directory	stack are numbered
		   from	the top	starting at 0.

	   pushd
	   pushd name
	   pushd +n
		   With	no arguments, pushd exchanges the top two elements of
		   the directory stack.	 Given a name argument,	pushd changes
		   to the new directory	(ala cd) and pushes the	old current
		   working directory (as in cwd) onto the directory stack.
		   With	a numeric argument, pushd 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 num-
		   bered from the top starting at 0.

	   rehash  Causes the internal hash table of the contents of the di-
		   rectories in	the path variable to be	recomputed.  This is
		   needed if new commands are added to directories in the path
		   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 a	system direc-
		   tory.

	   repeat count	command
		   The specified command, which	is subject to the same re-
		   strictions as the command in	the one	line if	statement
		   above, is executed count times.  I/O	redirections occur ex-
		   actly once, even if count is	0.

	   set
	   set name
	   set name=word
	   set name[index]=word
	   set name=(wordlist)
		   The first form of the command shows the value of all	shell
		   variables.  Variables that have other than a	single word as
		   their value print as	a parenthesized	word list.  The	second
		   form	sets name to the null string.  The third form sets
		   name	to the single word.  The fourth	form sets the index'th
		   component of	name to	word; this component must already ex-
		   ist.	 The final form	sets name to the list of words in
		   wordlist.  The value	is always command and filename ex-
		   panded.

		   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.

	   setenv
	   setenv name
	   setenv name value
		   The first form lists	all current environment	variables.  It
		   is equivalent to printenv(1).  The last form	sets the value
		   of environment variable name	to be value, a single string.
		   The second form sets	name to	an empty string.  The most
		   commonly used environment variables USER, TERM, and PATH
		   are automatically imported to and exported from the csh
		   variables user, term, and path; there is no need to use
		   setenv for these.

	   shift
	   shift variable
		   The members of argv are shifted to the left,	discarding
		   argv[1].  It	is an error for	argv not to be set or to have
		   less	than one word as value.	 The second form performs the
		   same	function on the	specified variable.

	   source name
	   source -h name
		   The shell reads commands from name.	source commands	may be
		   nested; if they are nested too deeply the shell may run out
		   of file descriptors.	 An error in a source at any level
		   terminates all nested source	commands.  Normally input dur-
		   ing source commands is not placed on	the history list; the
		   -h option causes the	commands to be placed on the history
		   list	without	being executed.

	   stop
	   stop	%job ...
		   Stops the current or	specified jobs that are	executing in
		   the background.

	   suspend
		   Causes the shell to stop in its tracks, much	as if it had
		   been	sent a stop signal with	^Z.  This is most often	used
		   to stop shells started by su(1).

	   switch (string)
	   case	str1:
	       ...
	       breaksw
	       ...
	   default:
	       ...
	       breaksw
	   endsw   Each	case label is successively matched against the speci-
		   fied	string,	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 the "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	breaksw	causes execution to continue
		   after the endsw.  Otherwise control may fall	through	case
		   labels and the default label	as in C.  If no	label matches
		   and there is	no default, execution continues	after the
		   endsw.

	   time
	   time	command
		   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 time variable is printed.	If necessary,
		   an extra shell is created to	print the time statistic when
		   the command completes.

	   umask
	   umask value
		   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	write access for users in the
		   group or others.

	   unalias pattern
		   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 unaliased.

	   unhash  Use of the internal hash table to speed location of exe-
		   cuted programs is disabled.

	   unlimit
	   unlimit resource
	   unlimit -h
	   unlimit -h resource
		   Removes the limitation on resource.	If no resource is
		   specified, then all resource	limitations are	removed.  If
		   -h is given,	the corresponding hard limits are removed.
		   Only	the superuser may do this.

	   unset pattern
		   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 unset.

	   unsetenv pattern
		   Removes all variables whose names match the specified pat-
		   tern	from the environment.  See also	the setenv command
		   above and printenv(1).

	   wait	   Wait	for all	background jobs.  If the shell is interactive,
		   then	an interrupt can disrupt the wait.  After the inter-
		   rupt, the shell prints names	and job	numbers	of all jobs
		   known to be outstanding.

	   which command
		   Displays the	resolved command that will be executed by the
		   shell.

	   while (expr)
	   ...
	   end	   While the specified expression evaluates to non-zero, the
		   commands between the	while and the matching end are evalu-
		   ated.  break	and continue may be used to terminate or con-
		   tinue the loop prematurely.	(The while and end must	appear
		   alone on their input	lines.)	 Prompting occurs here the
		   first time through the loop as for the foreach statement if
		   the input is	a terminal.

	   %job	   Brings the specified	job into the foreground.

	   %job	&  Continues the specified job in the background.

	   @
	   @ name= expr
	   @ name[index]= expr
		   The first form prints the values of all the shell vari-
		   ables.  The second form sets	the specified name to the
		   value of expr.  If the expression contains `<', `>',	`&' or
		   `|' then at least this part of the expression must be
		   placed within `(' `)'.  The third form assigns the value of
		   expr	to the index'th	argument of name.  Both	name and its
		   index'th component must already exist.

		   The operators `*=', `+=', etc. are available	as in C.  The
		   space separating the	name from the assignment operator is
		   optional.  Spaces are, however, mandatory in	separating
		   components of expr, which would otherwise be	single words.

		   Special postfix `++'	and `--' operators increment and
		   decrement name respectively;	i.e., "@ i++".

   Pre-defined and environment variables
     The following variables have special meaning to the shell.	 Of these,
     argv, cwd,	home, path, prompt, shell and status are always	set by the
     shell.  Except for	cwd and	status,	this setting occurs only at initial-
     ization; these variables will not then be modified	unless done explicitly
     by	the user.

     The shell copies the environment variable USER into the variable user,
     TERM into term, and HOME into home, 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 .cshrc as inferior csh processes will im-
     port the definition of path from the environment, and re-export it	if you
     then change it.

     argv	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.

     cdpath	Gives a	list of	alternate directories searched to find subdi-
		rectories in chdir commands.

     cwd	The full pathname of the current directory.

     echo	Set when the -x	command-line option is given.  Causes each
		command	and its	arguments to be	echoed just before it is exe-
		cuted.	For non-built-in commands all expansions occur before
		echoing.  Built-in commands are	echoed before command and
		filename substitution, since these substitutions are then done
		selectively.

     filec	Enable file name completion.

     histchars	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.

     histfile	Can be set to the pathname where history is going to be
		saved/restored.

     history	Can be given a numeric value to	control	the size of the	his-
		tory list.  Any	command	that has been referenced in this many
		events will not	be discarded.  Too large values	of history may
		run the	shell out of memory.  The last executed	command	is al-
		ways saved on the history list.

     home	The home directory of the invoker, initialized from the	envi-
		ronment.  The filename expansion of "~"	refers to this vari-
		able.

     ignoreeof	If set the shell ignores end-of-file from input	devices	which
		are terminals.	This prevents shells from accidentally being
		killed by control-Ds.

     mail	The files where	the shell checks for mail.  This checking is
		done after each	command	completion that	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 mail 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	name" when there is mail in the	file name.

     noclobber	As described in	the section on Input/output, restrictions are
		placed on output redirection to	ensure that files are not ac-
		cidentally destroyed, and that `>>' redirections refer to ex-
		isting files.

     noglob	If set,	filename expansion is inhibited.  This inhibition is
		most useful in shell scripts that are not dealing with file-
		names, or after	a list of filenames has	been obtained and fur-
		ther expansions	are not	desirable.

     nonomatch	If set,	it is not an error for a filename expansion to not
		match any existing files; instead 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.

     notify	If set,	the shell notifies asynchronously of job completions;
		the default is to present job completions just before printing
		a prompt.

     path	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 path variable then
		only full path names will execute.  The	usual search path is
		".", "/bin", "/usr/bin", "/sbin" and "/usr/sbin", but this may
		vary from system to system.  For the superuser the default
		search path is "/bin", "/usr/bin", "/sbin", and	"/usr/sbin".
		A shell	that is	given neither the -c nor the -t	option will
		normally hash the contents of the directories in the path
		variable after reading .cshrc, and each	time the path variable
		is reset.  If new commands are added to	these directories
		while the shell	is active, it may be necessary to do a rehash
		or the commands	may not	be found.

     prompt	The string that	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 preced-
		ing `\'	is given.  Default is the first	part of	the hostname,
		followed by "%", or "#"	for the	superuser.

     savehist	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 that 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 savehist will slow down
		the shell during start up.  If savehist	is just	set, the shell
		will use the value of history.

     shell	The file in which the shell resides.  This variable is used in
		forking	shells to interpret files that have execute bits set,
		but which are not executable by	the system.  (See the descrip-
		tion of	Non-built-in command execution below.)	Initialized to
		the (system-dependent) home of the shell.

     status	The status returned by the last	command.  If it	terminated ab-
		normally, then 0200 is added to	the status.  Built-in commands
		that fail return exit status 1,	all other built-in commands
		set status to 0.

     time	Controls automatic timing of commands.	If set,	then any com-
		mand that 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
		real time to be	printed	when it	terminates.

     verbose	Set by the -v command-line option, causes the words of each
		command	to be printed after history substitution.

   Non-built-in	command	execution
     When a command to be executed is found to not be a	built-in command the
     shell attempts to execute the command via execve(2).  Each	word in	the
     variable path names a directory from which	the shell will attempt to exe-
     cute the command.	If it is given neither a -c nor	a -t option, the shell
     will hash the names in these directories into an internal table so	that
     it	will only try an exec in a directory if	there is a possibility that
     the command resides there.	 This shortcut greatly speeds command location
     when many directories are present in the search path.  If this mechanism
     has been turned off (via unhash), or if the shell was given a -c or -t
     argument, and in any case for each	directory component of path that 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 execute.

     Parenthesized commands are	always executed	in a sub-shell.	 Thus

	   (cd;	pwd); pwd

     prints the	home directory;	leaving	you where you were (printing this af-
     ter the home directory), while

	   cd; pwd

     leaves you	in the home directory.	Parenthesized commands are most	often
     used to prevent chdir 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 alias for shell then the words of the alias	will be
     prepended to the argument list to form the	shell command.	The first word
     of	the alias should be the	full path name of the shell (e.g., "$shell").
     Note that this is a special, late occurring, case of alias	substitution,
     and only allows words to be prepended to the argument list	without
     change.

   Signal handling
     The shell normally	ignores	SIGQUIT	signals.  Jobs running detached	(ei-
     ther by & or the bg 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 in-
     terrupts and terminate signals in shell scripts can be controlled by
     onintr.  Login shells catch the SIGTERM (terminate) signal; otherwise
     this signal is passed on to children from the state in the	shell's	par-
     ent.  Interrupts are not allowed when a login shell is reading the	file
     .logout.

LIMITATIONS
     Word lengths: Words can be	no longer than 1024 characters.	 The number of
     arguments to a command that involves filename expansion is	limited	to
     1/6th the number of characters allowed in an argument list.  Command sub-
     stitutions	may substitute no more characters than are allowed in an argu-
     ment list.	 To detect looping, the	shell restricts	the number of alias
     substitutions on a	single line to 20.

FILES
     ~/.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"

SEE ALSO
     sh(1), access(2), execve(2), fork(2), pipe(2), setrlimit(2), umask(2),
     wait(2), killpg(3), sigvec(3), tty(4), environ(7),	script(7)

HISTORY
     csh first appeared	in 2BSD.  It was a first implementation	of a command
     language interpreter incorporating	a history mechanism (see History
     substitutions), job control facilities (see Jobs),	interactive file name
     and user name completion (see File	name completion), and a	C-like syntax.
     There are now many	shells that also have these mechanisms,	plus a few
     more (and maybe some bugs too), which are available through the usenet.

AUTHORS
     Bill Joy, 1978.  Job control and directory	stack features first imple-
     mented 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 by	Christos S. Zoulas, Cornell Univer-
     sity.

BUGS
     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 in-
     ternally.

     Shell built-in functions are not stoppable/restartable.  Command se-
     quences of	the form "a ; b	; c" are also not handled gracefully when
     stopping is attempted.  If	you suspend `b', the shell will	immediately
     execute `c'.  This	is especially noticeable if this expansion results
     from an alias.  It	suffices to place the sequence of commands in ()'s to
     force it to a sub-shell; 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	instead	of aliases.

     Commands within loops, prompted for by `?', are not placed	on the history
     list.  Control structure should be	parsed instead of 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.

     The way the filec facility	is implemented is ugly and expensive.

BSD			       November	10, 2018			   BSD

NAME | SYNOPSIS | DESCRIPTION | LIMITATIONS | FILES | SEE ALSO | HISTORY | AUTHORS | BUGS

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