+.de sh
+.br
+.ne 5
+.PP
+\fB\\$1\fR
+.PP
+..
+.if n .ds ua \o'^|'
+.if t .ds ua \(ua
+.if n .ds aa '
+.if t .ds aa \(aa
+.if n .ds ga `
+.if t .ds ga \(ga
+.if t .tr *\(**
+.TH CSH 1 9/1/81
+.UC 4
+.SH NAME
+csh \- a shell (command interpreter) with C-like syntax
+.SH SYNOPSIS
+.B csh
+[
+.B \-cef\^instvVxX
+] [
+arg ...
+]
+.SH DESCRIPTION
+.I Csh
+is a first implementation of a command language interpreter
+incorporating a history mechanism (see
+.B "History Substitutions)"
+job control facilities
+(see
+.B Jobs)
+and a C-like syntax.
+So as to be able to use its job control facilities, users of
+.I csh
+must (and automatically) use the new tty driver summarized in
+.IR newtty (4)
+and fully described in
+.IR tty (4).
+This new tty driver allows generation of interrupt characters
+from the keyboard to tell jobs to stop.
+See
+.IR stty (1)
+for details on setting options in the new tty driver.
+.PP
+An instance of
+.I csh
+begins by executing commands from the file `.cshrc'
+in the
+.I home
+directory of the invoker.
+If this is a login shell then it also executes commands from the file
+`.login' there.
+It is typical for users on crt's to put the command ``stty crt'' in their
+.I \&.login
+file, and to also invoke
+.IR tset (1)
+there.
+.PP
+In the normal case, the shell will then begin reading commands from the
+terminal, prompting with `% '.
+Processing of arguments and the use of the shell to process files
+containing command scripts will be described later.
+.PP
+The shell then repeatedly performs the following actions:
+a line of command input is read and broken into
+.I words.
+This sequence of words is placed on the command history list and then parsed.
+Finally each command in the current line is executed.
+.PP
+When a login shell terminates it executes commands from the file `.logout'
+in the users home directory.
+.sh "Lexical structure"
+The shell splits input lines into words at blanks and tabs with the
+following exceptions.
+The characters
+`&' `|' `;' `<' `>' `(' `)'
+form separate words.
+If doubled in `&&', `|\|\||', `<<' or `>>' these pairs form single words.
+These parser metacharacters may be made part of other words, or prevented their
+special meaning, by preceding them with `\e'.
+A newline preceded by a `\e' is equivalent to a blank.
+.PP
+In addition strings enclosed in matched pairs of quotations,
+`\*(aa', `\*(ga' or `"',
+form parts of a word; metacharacters in these strings, including blanks
+and tabs, do not form separate words.
+These quotations have semantics to be described subsequently.
+Within pairs of `\'' or `"' characters a newline preceded by a `\e' gives
+a true newline character.
+.PP
+When the shell's input is not a terminal,
+the character `#' introduces a comment which continues to the end of the
+input line.
+It is prevented this special meaning when preceded by `\e'
+and in quotations using `\`', `\'', and `"'.
+.sh "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 commands separated by `|' characters
+forms a pipeline.
+The output of each command in a pipeline is connected to the input of the next.
+Sequences of pipelines may be separated by `;', and are then executed
+sequentially.
+A sequence of pipelines may be executed without immediately
+waiting for it to terminate by following it with an `&'.
+.PP
+Any of the above may be placed in `(' `)' to form a simple command (which
+may be a component of a pipeline, etc.)
+It is also possible to separate pipelines with `|\|\||' or `&&' indicating,
+as in the C language,
+that the second is to be executed only if the first fails or succeeds
+respectively. (See
+.I Expressions.)
+.sh "Jobs"
+The shell associates a \fIjob\fR with each pipeline. It keeps
+a table of current jobs, printed by the
+\fIjobs\fR command, and assigns them small integer numbers. When
+a job is started asynchronously with `&', the shell prints a line which looks
+like:
+.PP
+.DT
+ [1] 1234
+.PP
+indicating that the jobs which was started asynchronously was job number
+1 and had one (top-level) process, whose process id was 1234.
+.PP
+If you are running a job and wish to do something else you may hit the key
+\fB^Z\fR (control-Z) which sends a STOP signal to the current job.
+The shell will then normally indicate that the job has been `Stopped',
+and print another prompt. You can then manipulate the state of this job,
+putting it in the background with the \fIbg\fR command, or run some other
+commands and then eventually bring the job back into the foreground with
+the foreground command \fIfg\fR. A \fB^Z\fR takes effect immediately and
+is like an interrupt in that pending output and unread input are discarded
+when it is typed. There is another special key \fB^Y\fR which does
+not generate a STOP signal until a program attempts to
+.IR read (2)
+it.
+This can usefully be typed ahead when you have prepared some commands
+for a job which you wish to stop after it has read them.
+.PP
+A job being run in the background will stop if it tries to read
+from the terminal. Background jobs are normally allowed to produce output,
+but this can be disabled by giving the command ``stty tostop''.
+If you set this
+tty option, then background jobs will stop when they try to produce
+output like they do when they try to read input.
+.PP
+There are several ways to refer to jobs in the shell. The character
+`%' introduces a job name. If you wish to refer to job number 1, you can
+name it as `%1'. Just naming a job brings it to the foreground; thus
+`%1' is a synonym for `fg %1', bringing job 1 back into the foreground.
+Similarly saying `%1 &' resumes job 1 in the background.
+Jobs can also be named by prefixes of the string typed in to start them,
+if these prefixes are unambiguous, thus `%ex' would normally restart
+a suspended
+.IR 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
+.I string,
+if there is only one such job.
+.PP
+The shell maintains a notion of the current and previous jobs.
+In output pertaining to jobs, the current job is marked with a `+'
+and the previous job with a `\-'. The abbreviation `%+' refers
+to the current job and `%\-' refers to the previous job. For close
+analogy with the syntax of the
+.I history
+mechanism (described below),
+`%%' is also a synonym for the current job.
+.sh "Status reporting"
+This shell learns immediately whenever a process changes state.
+It normally 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
+.I notify,
+the shell will notify you immediately of changes of status in background
+jobs.
+There is also a shell command
+.I notify
+which marks a single process so that its status changes will be immediately
+reported. By default
+.I notify
+marks the current process;
+simply say `notify' after starting a background job to mark it.
+.PP
+When you try to leave the shell while jobs are stopped, you will
+be warned that `You have stopped jobs.' You may use the \fIjobs\fR
+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.
+.sh Substitutions
+We now describe the various transformations the shell performs on the
+input in the order in which they occur.
+.sh "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
+.B anywhere
+in the input stream (with the proviso that they
+.B "do not"
+nest.)
+This `!' may be preceded by an `\e' 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 `\*(ua'.
+This special abbreviation will be described later.)
+Any input line which contains history substitution is echoed on the terminal
+before it is executed as it could have been typed without history substitution.
+.PP
+Commands input from the terminal which consist of one or more words
+are saved on the history list.
+The history substitutions reintroduce sequences of words from these
+saved commands into the input stream.
+The size of which is controlled by the
+.I history
+variable; the previous command is always retained, regardless of its value.
+Commands are numbered sequentially from 1.
+.PP
+For definiteness, consider the following output from the
+.I history
+command:
+.PP
+.DT
+.br
+ \09 write michael
+.br
+ 10 ex write.c
+.br
+ 11 cat oldwrite.c
+.br
+ 12 diff *write.c
+.PP
+The commands are shown with their event numbers.
+It is not usually necessary to use event numbers, but the current event
+number can be made part of the
+.I prompt
+by placing an `!' in the prompt string.
+.PP
+With the current event 13 we can refer to previous events by event
+number `!11', relatively as in `!\-2' (referring to the same event),
+by a prefix of a command word
+as in `!d' for event 12 or `!wri' for event 9, or by a string contained in
+a word in the command as in `!?mic?' also referring to event 9.
+These forms, without further modification, simply 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 essentially a
+.I redo.
+.PP
+To select words from an event we can follow the event specification by
+a `:' and a designator for the desired words.
+The words of a 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:
+.PP
+.DT
+.nf
+ 0 first (command) word
+ \fIn\fR \fIn\fR\|'th argument
+ \*(ua first argument, i.e. `1'
+ $ last argument
+ % word matched by (immediately preceding) ?\fIs\fR\|? search
+ \fIx\fR\|\-\fIy\fR range of words
+ \-\fIy\fR abbreviates `0\-\fIy\fR\|'
+ * abbreviates `\*(ua\-$', or nothing if only 1 word in event
+ \fIx\fR\|* abbreviates `\fIx\fR\|\-$'
+ \fIx\fR\|\- like `\fIx\fR\|*' but omitting word `$'
+.fi
+.PP
+The `:' separating the event specification from the word designator
+can be omitted if the argument selector begins with a `\*(ua', `$', `*'
+`\-' or `%'.
+After the optional word designator can be
+placed a sequence of modifiers, each preceded by a `:'.
+The following modifiers are defined:
+.ta .5i 1.2i
+.PP
+.nf
+ 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/\fIl\fR\|/\fIr\fR\|/ Substitute \fIl\fR for \fIr\fR
+ t Remove all leading pathname components, leaving the tail.
+ & Repeat the previous substitution.
+ g Apply the change globally, prefixing the above, e.g. `g&'.
+ p Print the new command but do not execute it.
+ q Quote the substituted words, preventing further substitutions.
+ x Like q, but break into words at blanks, tabs and newlines.
+.fi
+.PP
+Unless preceded by a `g' the modification is applied only to the first
+modifiable word. With substitutions, it is an error for no word to be
+applicable.
+.PP
+The left hand side of substitutions are not regular expressions in the sense
+of the editors, but rather strings.
+Any character may be used as the delimiter in place of `/';
+a `\e' quotes the delimiter into the
+.IR l ""
+and
+.IR r ""
+strings.
+The character `&' in the right hand side is replaced by the text from
+the left.
+A `\e' quotes `&' also.
+A null
+.IR l ""
+uses the previous string either from a
+.IR l ""
+or from a
+contextual scan string
+.IR s ""
+in `!?\fIs\fR\|?'.
+The trailing delimiter in the substitution may be omitted if a newline
+follows immediately as may the trailing `?' in a contextual scan.
+.PP
+A history reference may be given without an event specification, e.g. `!$'.
+In this case the reference is to the previous command unless a previous
+history reference occurred on the same line in which case this form repeats
+the previous reference.
+Thus `!?foo?\*(ua !$' gives the first and last arguments
+from the command matching `?foo?'.
+.PP
+A special abbreviation of a history reference occurs when the first
+non-blank character of an input line is a `\*(ua'.
+This is equivalent to `!:s\*(ua' providing a convenient shorthand for substitutions
+on the text of the previous line.
+Thus `\*(ualb\*(ualib' 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 which follow.
+Thus, after `ls \-ld ~paul' we might do `!{l}a' to do `ls \-ld ~paula',
+while `!la' would look for a command starting `la'.
+.PP
+.if n .ul
+\fBQuotations\ with\ \'\ and\ "\fR
+.PP
+The quotation of strings by `\'' and `"' can be used
+to prevent all or some of the remaining substitutions.
+Strings enclosed in `\'' are prevented any further interpretation.
+Strings enclosed in `"' are yet variable and command expanded
+as described below.
+.PP
+In both cases the resulting text becomes (all or part of) a single word;
+only in one special case (see
+.I "Command Substitition"
+below) does a `"' quoted string yield parts of more than one word;
+`\'' quoted strings never do.
+.sh "Alias substitution"
+The shell maintains a list of aliases which can be established, displayed
+and modified by the
+.I alias
+and
+.I 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 which is the alias for that command is reread
+with the history mechanism available
+as though that command were the previous input line.
+The resulting words replace the
+command and argument list.
+If no reference is made to the history list, then the argument list is
+left unchanged.
+.PP
+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 !\*(ua /etc/passwd' then
+`lookup bill' would map to `grep bill /etc/passwd'.
+.PP
+If an alias is found, the word transformation of the input text
+is performed 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.
+.PP
+Note that the mechanism allows aliases to introduce parser metasyntax.
+Thus we can `alias print \'pr \e!* \||\| lpr\'' to make a command which
+.I pr's
+its arguments to the line printer.
+.sh "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
+.I argv
+variable is an image of the shell's argument list, and words of this
+variable's value are referred to in special ways.
+.PP
+The values of variables may be displayed and changed by using the
+.I set
+and
+.I 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
+.I verbose
+variable is a toggle which causes command input to be echoed.
+The setting of this variable results from the
+.B \-v
+command line option.
+.PP
+Other operations treat variables numerically.
+The `@' command permits numeric 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 considered to be
+zero, and the second and subsequent words of multiword values are ignored.
+.PP
+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 `\e' except
+within `"'s where it
+.B always
+occurs, and within `\''s where it
+.B never
+occurs.
+Strings quoted by `\*(ga' are interpreted later (see
+.I "Command substitution"
+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.
+.PP
+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.
+.PP
+Unless enclosed in `"' or given the `:q' modifier the results of variable
+substitution may eventually be command and filename substituted.
+Within `"' a variable whose value consists of multiple words expands to a
+(portion of) a single word, with the words of the variables value
+separated 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.
+.PP
+The following metasequences are provided for introducing variable values into
+the shell input.
+Except as noted, it is an error to reference a variable which is not set.
+.HP 5
+$name
+.br
+.ns
+.HP 5
+${name}
+.br
+Are replaced by the words of the value of variable
+.I name,
+each separated by a blank.
+Braces insulate
+.I name
+from following characters which would otherwise be part of it.
+Shell variables have names consisting of up to 20 letters and digits
+starting with a letter. The underscore character is considered a letter.
+.br
+If
+.I name
+is not a shell variable, but is set in the environment, then
+that value is returned (but \fB:\fR modifiers and the other forms
+given below are not available in this case).
+.HP 5
+$name[selector]
+.br
+.ns
+.HP 5
+${name[selector]}
+.br
+May be used to select only some of the words from the value of
+.I name.
+The selector is subjected to `$' substitution and may consist of a single
+number or two numbers separated by a `\-'.
+The first word of a variables value is numbered `1'.
+If the first number of a range is omitted it defaults to `1'.
+If the last member of a range is omitted it defaults to `$#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.
+.HP 5
+$#name
+.br
+.ns
+.HP 5
+${#name}
+.br
+Gives the number of words in the variable.
+This is useful for later use in a `[selector]'.
+.HP 5
+$0
+.br
+Substitutes the name of the file from which command input is being read.
+An error occurs if the name is not known.
+.HP 5
+$number
+.br
+.ns
+.HP 5
+${number}
+.br
+Equivalent to `$argv[number]'.
+.HP 5
+$*
+.br
+Equivalent to `$argv[*]'.
+.PP
+The modifiers `: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.
+.B "The current implementation allows only one `:' modifier on each `$' expansion."
+.PP
+The following substitutions may not be modified with `:' modifiers.
+.HP 5
+$?name
+.br
+.ns
+.HP 5
+${?name}
+.br
+Substitutes the string `1' if name is set, `0' if it is not.
+.HP 5
+$?0
+.br
+Substitutes `1' if the current input filename is know, `0' if it is not.
+.HP 5
+$$
+.br
+Substitute the (decimal) process number of the (parent) shell.
+.HP 5
+$<
+.br
+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.
+.sh "Command and filename substitution"
+The remaining substitutions, command and filename substitution,
+are applied selectively to the arguments of builtin commands.
+This means that portions of expressions which are not evaluated are
+not subjected to these expansions.
+For commands which are not internal to the shell, the command
+name is substituted separately from the argument list.
+This occurs very late,
+after input-output redirection is performed, and in a child
+of the main shell.
+.sh "Command substitution"
+Command substitution is indicated by a command enclosed in `\*(ga'.
+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 replacing the original string.
+Within `"'s, only newlines force new words; blanks and tabs are preserved.
+.PP
+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.
+.sh "Filename substitution"
+If a word contains any of the characters `*', `?', `[' or `{'
+or begins with the character `~', then that word is a candidate for
+filename substitution, also known as `globbing'.
+This word is then regarded as a pattern, and replaced with an alphabetically
+sorted list of file names which match the pattern.
+In a list of words specifying filename substitution 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.
+.PP
+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 character.
+The sequence `[...]' matches any one of the characters enclosed.
+Within `[...]',
+a pair of characters separated by `\-' matches any character lexically between
+the two.
+.PP
+The character `~' at the beginning of a filename is used to refer to home
+directories.
+Standing alone, i.e. `~' it expands to the invokers home directory as reflected
+in the value of the variable
+.I 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 appears not at the beginning of a word,
+it is left undisturbed.
+.PP
+The metanotation `a{b,c,d}e' is a shorthand for `abe ace ade'.
+Left to right order is preserved, with results of matches being sorted
+separately at a low level to preserve this order.
+This construct may be nested.
+Thus `~source/s1/{oldls,ls}.c' expands to
+`/usr/source/s1/oldls.c /usr/source/s1/ls.c'
+whether or not these files exist without any chance of error
+if the home directory for `source' is `/usr/source'.
+Similarly `../{memo,*box}' might expand to `../memo ../box ../mbox'.
+(Note that `memo' was not sorted with the results of matching `*box'.)
+As a special case `{', `}' and `{}' are passed undisturbed.
+.sh Input/output
+The standard input and standard output of a command may be redirected
+with the following syntax:
+.HP 5
+< name
+.br
+Open file
+.I name
+(which is first variable, command and filename expanded) as the standard
+input.
+.HP 5
+<< word
+.br
+Read the shell input up to a line which is identical to
+.I word.
+.I Word
+is not subjected to variable, filename or command substitution,
+and each input line is compared to
+.I word
+before any substitutions are done on this input line.
+Unless a quoting `\e', `"', `\*(aa' or `\*(ga' appears in
+.I word
+variable and command substitution is performed on the intervening lines,
+allowing `\e' to quote `$', `\e' and `\*(ga'.
+Commands which are substituted have all blanks, tabs, and newlines
+preserved, except for the final newline which is dropped.
+The resultant text is placed in an anonymous temporary file which
+is given to the command as standard input.
+.HP 5
+> name
+.br
+.ns
+.HP 5
+>! name
+.br
+.ns
+.HP 5
+>& name
+.br
+.ns
+.HP 5
+>&! name
+.br
+The file
+.I name
+is used as standard output.
+If the file does not exist then it is created;
+if the file exists, its is truncated, its previous contents being lost.
+.IP
+If the variable
+.I 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 accidental destruction of files.
+In this case the `!' forms can be used and suppress this check.
+.IP
+The forms involving `&' route the diagnostic output into the specified
+file as well as the standard output.
+.I Name
+is expanded in the same way as `<' input filenames are.
+.HP 5
+>> name
+.br
+.ns
+.HP 5
+>>& name
+.br
+.ns
+.HP 5
+>>! name
+.br
+.ns
+.HP 5
+>>&! name
+.br
+Uses file
+.I name
+as standard output like `>' but places output at the end of the file.
+If the variable
+.I noclobber
+is set, then
+it is an error for the file not to exist unless
+one of the `!' forms is given.
+Otherwise similar to `>'.
+.PP
+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
+.B not
+modified to be the empty file `/dev/null'; rather the standard input
+remains as the original standard input of the shell. If this is a terminal
+and if the process attempts to read from the terminal, then the process
+will block and the user will be notified (see
+.B Jobs
+above.)
+.PP
+Diagnostic output may be directed through a pipe with the standard output.
+Simply use the form `|\|&' rather than just `|'.
+.sh Expressions
+A number of the builtin commands (to be described subsequently)
+take expressions, in which the operators are similar to those of C, with
+the same precedence.
+These expressions appear in the
+.I @,
+.I exit,
+.I if,
+and
+.I while
+commands.
+The following operators are available:
+.DT
+.PP
+ |\|\|| && | \*(ua & == != =~ !~ <= >= < > << >> + \- * / % ! ~ ( )
+.PP
+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
+.I 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
+.I switch
+statement in shell scripts when all that is really needed is pattern matching.
+.PP
+Strings which begin with `0' are considered octal numbers.
+Null or missing arguments are considered `0'.
+The result of all expressions are strings,
+which represent decimal numbers.
+It is important to note that no two components of an expression can appear
+in the same word; except when adjacent to components of expressions which
+are syntactically significant to the parser (`&' `|' `<' `>' `(' `)')
+they should be surrounded by spaces.
+.PP
+Also available in expressions as primitive operands are command executions
+enclosed in `{' and `}'
+and file enquiries of the form `\-\fIl\fR name' where
+.I l
+is one of:
+.PP
+.DT
+.nf
+ r read access
+ w write access
+ x execute access
+ e existence
+ o ownership
+ z zero size
+ f plain file
+ d directory
+.fi
+.PP
+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 command exits with status 0, otherwise they fail, returning
+false, i.e. `0'.
+If more detailed status information is required then the command
+should be executed outside of an expression and the variable
+.I status
+examined.
+.sh "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 but useful ways) from terminal input.
+These commands all operate by forcing the shell to reread or skip in its
+input and, due to the implementation, restrict the placement of some
+of the commands.
+.PP
+The
+.I foreach,
+.I switch,
+and
+.I while
+statements, as well as the
+.I if\-then\-else
+form of the
+.I if
+statement require that the major keywords appear in a single simple command
+on an input line as shown below.
+.PP
+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 accomplish the rereading
+implied by the loop.
+(To the extent that this allows, backward goto's will succeed on
+non-seekable inputs.)
+.sh "Builtin commands"
+Builtin commands are executed within the shell.
+If a builtin command occurs as any component of a pipeline
+except the last then it is executed in a subshell.
+.HP 5
+.B alias
+.br
+.ns
+.HP 5
+.BR alias " name"
+.br
+.ns
+.HP 5
+.BR alias " name wordlist"
+.br
+The first form prints all aliases.
+The second form prints the alias for name.
+The final form assigns the specified
+.I wordlist
+as the alias of
+.I name;
+.I wordlist
+is command and filename substituted.
+.I Name
+is not allowed to be
+.I alias
+or
+.I unalias.
+.HP 5
+.B alloc
+.br
+Shows the amount of dynamic core in use, broken down into used and
+free core, and address of the last location in the heap.
+With an argument shows each used and free block on the internal dynamic
+memory chain indicating its address, size, and whether it is used or free.
+This is a debugging command and may not work in production versions of the
+shell; it requires a modified version of the system memory allocator.
+.HP 5
+.B bg
+.br
+.ns
+.HP 5
+\fBbg\ %\fRjob\ ...
+.br
+Puts the current or specified jobs into the background, continuing them
+if they were stopped.
+.HP 5
+.B break
+.br
+Causes execution to resume after the
+.I end
+of the nearest enclosing
+.I foreach
+or
+.I while.
+The remaining commands on the current line are executed.
+Multi-level breaks are thus possible by writing them all on one line.
+.HP 5
+.B breaksw
+.br
+Causes a break from a
+.I switch,
+resuming after the
+.I endsw.
+.HP 5
+.BR case " label:"
+.br
+A label in a
+.I switch
+statement as discussed below.
+.HP 5
+.B cd
+.br
+.ns
+.HP 5
+.BR cd " name"
+.br
+.ns
+.HP 5
+.B chdir
+.br
+.ns
+.HP 5
+.BR chdir " name"
+.br
+Change the shells working directory to directory
+.I name.
+If no argument is given then change to the home directory of the user.
+.br
+If
+.I name
+is not found as a subdirectory of the current directory (and does not begin
+with `/', `./' or `../'), then each
+component of the variable
+.I cdpath
+is checked to see if it has a subdirectory
+.I name.
+Finally, if all else fails but
+.I name
+is a shell variable whose value begins with `/', then this
+is tried to see if it is a directory.
+.HP 5
+.B continue
+.br
+Continue execution of the nearest enclosing
+.I while
+or
+.I foreach.
+The rest of the commands on the current line are executed.
+.HP 5
+.B default:
+.br
+Labels the default case in a
+.I switch
+statement.
+The default should come after all
+.I case
+labels.
+.HP 5
+.BR "dirs"
+.br
+Prints the directory stack; the top of the stack is at the left,
+the first directory in the stack being the current directory.
+.HP 5
+.BR echo " wordlist"
+.br
+.ns
+.HP 5
+.BR "echo \-n" " wordlist"
+.br
+The specified words are written to the shells standard output, separated
+by spaces, and terminated with a newline unless the
+.B \-n
+option is specified.
+.HP 5
+.B else
+.br
+.ns
+.HP 5
+.B end
+.br
+.ns
+.HP 5
+.B endif
+.br
+.ns
+.HP 5
+.B endsw
+.br
+See the description of the
+.I foreach,
+.I if,
+.I switch,
+and
+.I while
+statements below.
+.HP 5
+.BR eval " arg ..."
+.br
+(As in
+.IR sh (1).)
+The arguments are read as input to the shell and the resulting
+command(s) executed. This is usually used to execute commands
+generated as the result of command or variable substitution, since
+parsing occurs before these substitutions. See
+.IR tset (1)
+for an example of using
+.I eval.
+.HP 5
+.BR exec " command"
+.br
+The specified command is executed in place of the current shell.
+.HP 5
+.B exit
+.br
+.ns
+.HP 5
+.BR exit (expr)
+.br
+The shell exits either with the value of the
+.I status
+variable (first form) or with the value of the specified
+.I expr
+(second form).
+.HP 5
+.B fg
+.br
+.ns
+.HP 5
+\fBfg\ %\fRjob\ ...
+.br
+Brings the current or specified jobs into the foreground, continuing them if
+they were stopped.
+.HP 5
+.BR foreach " name (wordlist)"
+.br
+.ns
+.HP 5
+\ ...
+.br
+.ns
+.HP 5
+.B end
+.br
+The variable
+.I name
+is successively set to each member of
+.I wordlist
+and the sequence of commands between this command and the matching
+.I end
+are executed.
+(Both
+.I foreach
+and
+.I end
+must appear alone on separate lines.)
+.IP
+The builtin command
+.I continue
+may be used to continue the loop prematurely and the builtin
+command
+.I break
+to terminate it prematurely.
+When this command is read from the terminal, the loop is read up once
+prompting with `?' before any statements in the loop are executed.
+If you make a mistake typing in a loop at the terminal you can rub it out.
+.HP 5
+.BR glob " wordlist"
+.br
+Like
+.I echo
+but no `\e' escapes are recognized and words are delimited
+by null characters in the output.
+Useful for programs which wish to use the shell to filename expand a list
+of words.
+.HP 5
+.BR goto " word"
+.br
+The specified
+.I 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.
+Execution continues after the specified line.
+.HP 5
+.BR hashstat
+.br
+Print a statistics line indicating how effective the internal hash
+table has been at locating commands (and avoiding
+.I exec's).
+An
+.I exec
+is attempted for each component of the
+.I path
+where the hash function indicates a possible hit, and in each component
+which does not begin with a `/'.
+.HP 5
+.B history
+.br
+.ns
+.HP 5
+.BI history " n"
+.br
+.ns
+.HP 5
+.BI "history \-r" " n"
+.br
+Displays the history event list; if \fIn\fR is given only the
+.I n
+most recent events are printed.
+The
+.B \-r
+option reverses the order of printout to be most recent first
+rather than oldest first.
+.HP 5
+.BR if " (expr) command"
+.br
+If the specified expression evaluates true, then the single
+.I command
+with arguments is executed.
+Variable substitution on
+.IR command ""
+happens early, at the same
+time it does for the rest of the
+.I if
+command.
+.I Command
+must be a simple command, not
+a pipeline, a command list, or a parenthesized command list.
+Input/output redirection occurs even if
+.I expr
+is false, when command is
+.B not
+executed (this is a bug).
+.HP 5
+.BR if " (expr) " "then"
+.br
+.ns
+.HP 5
+\ ...
+.br
+.ns
+.HP 5
+.BR else " " "if\fR (expr2) \fBthen"
+.br
+.ns
+.HP 5
+\ ...
+.br
+.ns
+.HP 5
+.B else
+.br
+.ns
+.HP 5
+\ ...
+.br
+.ns
+.HP 5
+.B endif
+.br
+If the specified
+.IR expr ""
+is true then the commands to the first
+.I else
+are executed; else if
+.IR expr2 ""
+is true then the commands to the
+second else are executed, etc.
+Any number of
+.I else-if
+pairs are possible; only one
+.I endif
+is needed.
+The
+.I else
+part is likewise optional.
+(The words
+.I else
+and
+.I endif
+must appear at the beginning of input lines;
+the
+.I if
+must appear alone on its input line or after an
+.I else.)
+.HP 5
+.B jobs
+.br
+.ns
+.HP 5
+.B "jobs \-l"
+.br
+Lists the active jobs; given the
+.B \-l
+options lists process id's in addition to the normal information.
+.HP 5
+\fBkill %\fRjob
+.br
+.ns
+.HP 5
+\fBkill\ \-\fRsig\ \fB%\fRjob\ ...
+.br
+.ns
+.HP 5
+\fBkill\fR\ pid
+.br
+.ns
+.HP 5
+\fBkill\ \-\fRsig\ pid\ ...
+.br
+.ns
+.HP 5
+\fBkill\ \-l\fR
+.br
+Sends either the TERM (terminate) signal or the
+specified signal to the specified jobs or processes.
+Signals are either given by number or by names (as given in
+.I /usr/include/signal.h,
+stripped of the prefix ``SIG'').
+The signal names are listed by ``kill \-l''.
+There is no default, saying just `kill' does not
+send a signal to the current job.
+If the signal being sent is TERM (terminate) or HUP (hangup),
+then the job or process will be sent a CONT (continue) signal as well.
+.HP
+\fBlimit\fR
+.br
+.ns
+.HP 5
+\fBlimit\fR \fIresource\fR
+.br
+.ns
+.HP 5
+\fBlimit\fR \fIresource\fR \fImaximum-use\fR
+.br
+Limits the consumption by the current process and each process
+it creates to not individually exceed \fImaximum-use\fR on the
+specified \fIresource\fR. If no \fImaximum-use\fR is given, then
+the current limit is printed; if no \fIresource\fR is given, then
+all limitations are given.
+.IP
+Resources controllable currently include \fIcputime\fR (the maximum
+number of cpu-seconds to be used by each process), \fIfilesize\fR
+(the largest single file which can be created), \fIdatasize\fR
+(the maximum growth of the data+stack region via
+.IR sbrk (2)
+beyond the end of the program text), \fIstacksize\fR (the maximum
+size of the automatically-extended stack region), and \fIcoredumpsize\fR
+(the size of the largest core dump that will be created).
+.IP
+The \fImaximum-use\fR may be given as a (floating point or integer)
+number followed by a scale factor. For all limits other than \fIcputime\fR
+the default scale is `k' or `kilobytes' (1024 bytes);
+a scale factor of `m' or `megabytes' may also be used.
+For
+.I cputime
+the default scaling is `seconds', while `m' for minutes
+or `h' for hours, or a time of the form `mm:ss' giving minutes
+and seconds may be used.
+.IP
+For both \fIresource\fR names and scale factors, unambiguous prefixes
+of the names suffice.
+.HP 5
+.B login
+.br
+Terminate a login shell, replacing it with an instance of
+.B /bin/login.
+This is one way to log off, included for compatibility with
+.IR sh (1).
+.HP 5
+.B logout
+.br
+Terminate a login shell.
+Especially useful if
+.I ignoreeof
+is set.
+.HP 5
+.B newgrp
+.br
+Changes the group identification of the caller; for details see
+.IR newgrp (1).
+A new shell is executed by
+.I newgrp
+so that the shell state is lost.
+.HP 5
+.B nice
+.br
+.ns
+.HP 5
+.BR nice " \+number"
+.br
+.ns
+.HP 5
+.BR nice " command"
+.br
+.ns
+.HP 5
+.BR nice " \+number command"
+.br
+The first form sets the
+.I nice
+for this shell to 4.
+The second form sets the
+.I nice
+to the given number.
+The final two forms run command at priority 4 and
+.I number
+respectively.
+The super-user may specify negative niceness by using `nice \-number ...'.
+Command is always executed in a sub-shell, and the restrictions
+place on commands in simple
+.I if
+statements apply.
+.HP 5
+.B nohup
+.br
+.ns
+.HP 5
+.BR "nohup" " command"
+.br
+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 effectively
+.I nohup'ed.
+.HP 5
+.B notify
+.br
+.ns
+.HP 5
+\fBnotify\ %\fRjob\ ...
+.br
+Causes the shell to notify the user asynchronously when the status of the
+current or specified jobs changes; normally notification is presented
+before a prompt. This is automatic if the shell variable
+.I notify
+is set.
+.HP 5
+.B onintr
+.br
+.ns
+.HP 5
+.BR onintr " \-"
+.br
+.ns
+.HP 5
+.BR onintr " label"
+.br
+Control the action of the shell on interrupts.
+The first form restores the default action of the shell on interrupts
+which is to terminate shell scripts or to return to the terminal command
+input level.
+The second form `onintr \-' causes all interrupts to be ignored.
+The final form causes the shell to execute a `goto label' when
+an interrupt is received or a child process terminates because
+it was interrupted.
+.IP
+In any case, if the shell is running detached and interrupts are
+being ignored, all forms of
+.I onintr
+have no meaning and interrupts
+continue to be ignored by the shell and all invoked commands.
+.HP 5
+.BR "popd"
+.br
+.ns
+.HP 5
+.BR "popd" " +n"
+.br
+Pops the directory stack, returning to the new top directory.
+With a argument `+\fIn\fR' discards the \fIn\fR\|th
+entry in the stack.
+The elements of the directory stack are numbered from 0 starting at the top.
+.HP 5
+.BR "pushd"
+.br
+.ns
+.HP 5
+.BR "pushd" " name"
+.br
+.ns
+.HP 5
+.BR "pushd" " +n"
+.br
+With no arguments,
+.I pushd
+exchanges the top two elements of the directory stack.
+Given a
+.I name
+argument,
+.I pushd
+changes to the new directory (ala
+.I cd)
+and pushes the old current working directory
+(as in
+.I csw)
+onto the directory stack.
+With a numeric argument, rotates the \fIn\fR\|th argument of the directory
+stack around to be the top element and changes to it. The members
+of the directory stack are numbered from the top starting at 0.
+.HP 5
+.BR rehash
+.br
+Causes the internal hash table of the contents of the directories in
+the
+.I path
+variable to be recomputed. This is needed if new commands are added
+to directories in the
+.I 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 one of the system directories.
+.HP 5
+.BR repeat " count command"
+.br
+The specified
+.I command
+which is subject to the same restrictions
+as the
+.I command
+in the one line
+.I if
+statement above,
+is executed
+.I count
+times.
+I/O redirections occur exactly once, even if
+.I count
+is 0.
+.HP 5
+.B set
+.br
+.ns
+.HP 5
+.BR set " name"
+.br
+.ns
+.HP 5
+.BR set " name=word"
+.br
+.ns
+.HP 5
+.BR set " name[index]=word"
+.br
+.ns
+.HP 5
+.BR set " name=(wordlist)"
+.br
+The first form of the command shows the value of all shell variables.
+Variables which have other than a single word as value print as a parenthesized
+word list.
+The second form sets
+.I name
+to the null string.
+The third form sets
+.I name
+to the single
+.I word.
+The fourth form sets
+the
+.I index'th
+component of name to word;
+this component must already exist.
+The final form sets
+.I name
+to the list of words in
+.I wordlist.
+In all cases the value is command and filename expanded.
+.IP
+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.
+.HP 5
+.BR setenv " name value"
+.br
+Sets the value of environment variable
+.I name
+to be
+.I value,
+a single string.
+The most commonly used environment variable USER, TERM, and PATH
+are automatically imported to and exported from the
+.I csh
+variables
+.I user,
+.I term,
+and
+.I path;
+there is no need to use
+.I setenv
+for these.
+.HP 5
+.B shift
+.br
+.ns
+.HP 5
+.BR shift " variable"
+.br
+The members of
+.I argv
+are shifted to the left, discarding
+.I argv[1].
+It is an error for
+.I 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.
+.HP 5
+.BR source " name"
+.br
+The shell reads commands from
+.I name.
+.I Source
+commands may be nested; if they are nested too deeply the shell may
+run out of file descriptors.
+An error in a
+.I source
+at any level terminates all nested
+.I source
+commands.
+Input during
+.I source
+commands is
+.B never
+placed on the history list.
+.HP 5
+.B stop
+.br
+.ns
+.HP 5
+\fBstop\ %\fRjob\ ...
+.br
+Stops the current or specified job which is executing in the background.
+.HP 5
+.B suspend
+.br
+.ns
+Causes the shell to stop in its tracks, much as if it had been sent a stop
+signal with \fB^Z\fR. This is most often used to stop shells started by
+.IR su (1).
+.HP 5
+.BR switch " (string)"
+.br
+.ns
+.HP 5
+.BR case " str1:"
+.br
+.ns
+.HP 5
+\ ...
+.br
+.ns
+.HP 5
+\
+.B breaksw
+.br
+.ns
+.HP 5
+\&...
+.br
+.ns
+.HP 5
+.B default:
+.br
+.ns
+.HP 5
+\ ...
+.br
+.ns
+.HP 5
+\
+.B breaksw
+.br
+.ns
+.HP 5
+.B endsw
+.br
+Each case label is successively matched, against the specified
+.I 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 a `default' label is found, then
+the execution begins after the default label.
+Each case label and the default label must appear at the beginning of a line.
+The command
+.I breaksw
+causes execution to continue after the
+.I endsw.
+Otherwise control may fall through case labels and default labels as in C.
+If no label matches and there is no default, execution continues after
+the
+.I endsw.
+.HP 5
+.B time
+.br
+.ns
+.HP 5
+.BR time " command"
+.br
+With no argument, a summary of time used by this shell and its children
+is printed.
+If arguments are given
+the specified simple command is timed and a time summary
+as described under the
+.I time
+variable is printed.
+If necessary, an extra shell is created to print the time
+statistic when the command completes.
+.HP 5
+.B umask
+.br
+.ns
+.HP 5
+.BR umask " value"
+.br
+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 access to the group and read and execute
+access to others or 022 giving all access except no write access for
+users in the group or others.
+.HP 5
+.BR unalias " pattern"
+.br
+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
+.I unaliased.
+.HP 5
+.BR unhash
+.br
+Use of the internal hash table to speed location of executed programs
+is disabled.
+.HP 5
+\fBunlimit\fR \fIresource\fR
+.br
+.ns
+.HP 5
+\fBunlimit\fR
+.br
+Removes the limitation on \fIresource\fR. If no \fIresource\fR
+is specified, then all \fIresource\fR limitations are removed.
+.HP 5
+.BR unset " pattern"
+.br
+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 error for nothing to be
+.I unset.
+.HP 5
+.BR unsetenv " pattern"
+.br
+Removes all variables whose name match the specified pattern from the
+environment. See also the
+.I setenv
+command above and
+.IR printenv (1).
+.HP 5
+.B wait
+.br
+All background jobs are waited for.
+It the shell is interactive, then an interrupt can disrupt the wait,
+at which time the shell prints names and job numbers of all jobs
+known to be outstanding.
+.HP 5
+.BR while " (expr)"
+.br
+.ns
+.HP 5
+\ ...
+.br
+.ns
+.HP 5
+.B end
+.br
+While the specified expression evaluates non-zero, the commands between
+the
+.I while
+and the matching end are evaluated.
+.I Break
+and
+.I continue
+may be used to terminate or continue the loop prematurely.
+(The
+.I while
+and
+.I end
+must appear alone on their input lines.)
+Prompting occurs here the first time through the loop as for the
+.I foreach
+statement if the input is a terminal.
+.HP 5
+\fB%\fRjob
+.br
+Brings the specified job into the foreground.
+.HP 5
+\fB%\fRjob \fB&\fR
+.br
+Continues the specified job in the background.
+.HP 5
+.B "@"
+.br
+.ns
+.HP 5
+.BR "@" " name = expr"
+.br
+.ns
+.HP 5
+.BR "@" " name[index] = expr"
+.br
+The first form prints the values of all the shell variables.
+The second form sets the specified
+.I name
+to the value of
+.I 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
+.I expr
+to the
+.I index'th
+argument of
+.I name.
+Both
+.I name
+and its
+.I index'th
+component must already exist.
+.IP
+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
+.I expr
+which would otherwise be single words.
+.IP
+Special postfix `++' and `\-\-' operators increment and decrement
+.I name
+respectively, i.e. `@ i++'.
+.sh "Pre-defined and environment variables"
+The following variables have special meaning to the shell.
+Of these,
+.I argv,
+.I cwd,
+.I home,
+.I path,
+.I prompt,
+.I shell
+and
+.I status
+are always set by the shell.
+Except for
+.I cwd
+and
+.I status
+this setting occurs only at initialization;
+these variables will not then be modified unless this is done
+explicitly by the user.
+.PP
+This shell copies the environment variable USER into the variable
+.I user,
+TERM into
+.I term,
+and
+HOME into
+.I home,
+and copies these back into the environment 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
+.I \&.cshrc
+as inferior
+.I csh
+processes will import the definition of
+.I path
+from the environment, and re-export it if you then change it.
+(It could be set once in the
+.I \&.login
+except that commands through
+.IR net (1)
+would not see the definition.)
+.TP 15
+.B argv
+\c
+Set to the arguments to the shell, it is from this variable that
+positional parameters are substituted, i.e. `$1' is replaced by
+`$argv[1]', etc.
+.TP 15
+.B cdpath
+\c
+Gives a list of alternate directories searched to find subdirectories
+in
+.I chdir
+commands.
+.TP 15
+.B cwd
+The full pathname of the current directory.
+.TP 15
+.B echo
+\c
+Set when the
+.B \-x
+command line option is given.
+Causes each command and its arguments
+to be echoed just before it is executed.
+For non-builtin commands all expansions occur before echoing.
+Builtin commands are echoed before command and filename substitution,
+since these substitutions are then done selectively.
+.TP 15
+.B histchars
+\c
+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 default character !.
+The second character of its value replaces the character \(ua in
+quick substitutions.
+.TP 15
+.B history
+\c
+Can be given a numeric value to control the size of the history list.
+Any command which has been referenced in this many events will not be
+discarded.
+Too large values of
+.I history
+may run the shell out of memory.
+The last executed command is always saved on the history list.
+.TP 15
+.B home
+\c
+The home directory of the invoker, initialized from the environment.
+The filename expansion of `\fB~\fR' refers to this variable.
+.TP 15
+.B ignoreeof
+\c
+If set the shell ignores
+end-of-file from input devices which are terminals.
+This prevents shells from accidentally being killed by control-D's.
+.TP 15
+.B mail
+\c
+The files where the shell checks for mail.
+This is done after each command completion which will result in a prompt,
+if a specified interval has elapsed.
+The shell says `You have new mail.'
+if the file exists with an access time not greater than its modify time.
+.IP
+If the first word of the value of
+.I mail
+is numeric it specifies a different mail checking interval, in seconds,
+than the default, which is 10 minutes.
+.IP
+If multiple mail files are specified, then the shell says
+`New mail in
+.IR name '
+when there is mail in the file
+.I name.
+.TP 15
+.B noclobber
+\c
+As described in the section on
+.I Input/output,
+restrictions are placed on output redirection to insure that
+files are not accidentally destroyed, and that `>>' redirections
+refer to existing files.
+.TP 15
+.B noglob
+\c
+If set, filename expansion is inhibited.
+This is most useful in shell scripts which are not dealing with filenames,
+or after a list of filenames has been obtained and further expansions
+are not desirable.
+.TP 15
+.B nonomatch
+\c
+If set, it is not an error for a filename expansion to not match any
+existing files; rather the primitive pattern is returned.
+It is still an error for the primitive pattern to be malformed, i.e.
+`echo [' still gives an error.
+.TP 15
+.B notify
+\c
+If set, the shell notifies asynchronously of job completions. The
+default is to rather present job completions just before printing
+a prompt.
+.TP 15
+.B path
+\c
+Each word of the path variable specifies a directory in which
+commands are to be sought for execution.
+A null word specifies the current directory.
+If there is no
+.I path
+variable then only full path names will execute.
+The usual search path is `.', `/bin' and `/usr/bin', but this
+may vary from system to system.
+For the super-user the default search path is `/etc', `/bin' and `/usr/bin'.
+A shell which is given neither the
+.B \-c
+nor the
+.B \-t
+option will normally hash the contents of the directories in the
+.I path
+variable after reading
+.I \&.cshrc,
+and each time the
+.I path
+variable is reset. If new commands are added to these directories
+while the shell is active, it may be necessary to give the
+.I rehash
+or the commands may not be found.
+.TP 15
+.B prompt
+\c
+The string which is printed before each command is read from
+an interactive terminal input.
+If a `!' appears in the string it will be replaced by the current event number
+unless a preceding `\e' is given.
+Default is `% ', or `# ' for the super-user.
+.TP 15
+.B shell
+\c
+The file in which the shell resides.
+This is used in forking shells to interpret files which have execute
+bits set, but which are not executable by the system.
+(See the description of
+.I "Non-builtin Command Execution"
+below.)
+Initialized to the (system-dependent) home of the shell.
+.TP 15
+.B status
+\c
+The status returned by the last command.
+If it terminated abnormally, then 0200 is added to the status.
+Builtin commands which fail return exit status `1',
+all other builtin commands set status `0'.
+.TP 15
+.B time
+\c
+Controls automatic timing of commands.
+If set, then any command which takes more than this many cpu seconds
+will cause a line giving user, system, and real times and a utilization
+percentage which is the ratio of user plus system times to real time
+to be printed when it terminates.
+.TP 15
+.B verbose
+\c
+Set by the
+.B \-v
+command line option, causes the words of each command to be printed
+after history substitution.
+.sh "Non-builtin command execution"
+When a command to be executed is found to not be a builtin command
+the shell attempts to execute the command via
+.IR exec (2).
+Each word in the variable
+.I path
+names a directory from which the shell will attempt to execute the command.
+If it is given neither a
+.B \-c
+nor a
+.B \-t
+option, the shell will hash the names in these directories into an internal
+table so that it will only try an
+.I exec
+in a directory if there is a possibility that the command resides there.
+This greatly speeds command location when a large number of directories
+are present in the search path.
+If this mechanism has been turned off (via
+.I unhash),
+or if the shell was given a
+.B \-c
+or
+.B \-t
+argument, and in any case for each directory component of
+.I path
+which does not begin with a `/',
+the shell concatenates with the given command name to form a path name
+of a file which it then attempts to execute.
+.PP
+Parenthesized commands are always executed in a subshell.
+Thus `(cd ; pwd) ; pwd' prints the
+.I home
+directory; leaving you where you were (printing this after the home directory),
+while `cd ; pwd' leaves you in the
+.I home
+directory.
+Parenthesized commands are most often used to prevent
+.I chdir
+from affecting the current shell.
+.PP
+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 an a new shell is spawned to read it.
+.PP
+If there is an
+.I alias
+for
+.I shell
+then the words of the alias will be prepended to the argument list to form
+the shell command.
+The first word of the
+.I alias
+should be the full path name of the shell
+(e.g. `$shell').
+Note that this is a special, late occurring, case of
+.I alias
+substitution,
+and only allows words to be prepended to the argument list without modification.
+.sh "Argument list processing"
+If argument 0 to the shell is `\-' then this
+is a login shell.
+The flag arguments are interpreted as follows:
+.TP 5
+.B \-c
+\c
+Commands are read from the (single) following argument which must
+be present.
+Any remaining arguments are placed in
+.I argv.
+.TP 5
+.B \-e
+\c
+The shell exits if any invoked command terminates abnormally
+or yields a non-zero exit status.
+.TP 5
+.B \-f
+\c
+The shell will start faster, because it will neither search for nor
+execute commands from the file
+`\&.cshrc' in the invokers home directory.
+.TP 5
+.B \-i
+\c
+The shell is interactive and prompts for its top-level input,
+even if it appears to not be a terminal.
+Shells are interactive without this option if their inputs
+and outputs are terminals.
+.TP 5
+.B \-n
+\c
+Commands are parsed, but not executed.
+This may aid in syntactic checking of shell scripts.
+.TP 5
+.B \-s
+\c
+Command input is taken from the standard input.
+.TP 5
+.B \-t
+\c
+A single line of input is read and executed.
+A `\e' may be used to escape the newline at the end of this
+line and continue onto another line.
+.TP 5
+.B \-v
+\c
+Causes the
+.I verbose
+variable to be set, with the effect
+that command input is echoed after history substitution.
+.TP 5
+.B \-x
+\c
+Causes the
+.I echo
+variable to be set, so that commands are echoed immediately before execution.
+.TP 5
+.B \-V
+\c
+Causes the
+.I verbose
+variable to be set even before `\&.cshrc' is executed.
+.TP 5
+.B \-X
+\c
+Is to
+.B \-x
+as
+.B \-V
+is to
+.B \-v.
+.PP
+After processing of flag arguments if arguments remain but none of the
+.B \-c,
+.B \-i,
+.B \-s,
+or
+.B \-t
+options was 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 systems use either the standard version 6 or version 7 shells
+whose shell scripts are not compatible with this shell, the shell will
+execute such a `standard' shell if the first character of a script
+is not a `#', i.e. if the script does not start with a comment.
+Remaining arguments initialize the variable
+.I argv.
+.sh "Signal handling"
+The shell normally ignores
+.I quit
+signals.
+Jobs running detached (either by `&' or the \fIbg\fR or \fB%... &\fR
+commands) are immune to signals generated from the keyboard, including
+hangups.
+Other signals have the values which the shell inherited from its parent.
+The shells handling of interrupts and terminate signals
+in shell scripts can be controlled by
+.I onintr.
+Login shells catch the
+.I terminate
+signal; otherwise this signal is passed on to children from the state in the
+shell's parent.
+In no case are interrupts allowed when a login shell is reading the file
+`\&.logout'.
+.SH AUTHOR
+William Joy.
+Job control and directory stack features first implemented by J.E. Kulp of
+I.I.A.S.A, Laxenburg, Austria,
+with different syntax than that used now.
+.SH FILES
+.ta 1.75i
+.nf
+~/.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'.
+.fi
+.SH LIMITATIONS
+Words can be no longer than 1024 characters.
+The system limits argument lists to 10240 characters.
+The number of arguments to a command which involves filename expansion
+is limited to 1/6'th the number of characters allowed in an argument list.
+Command substitutions may substitute no more characters than are
+allowed in an argument list.
+To detect looping, the shell restricts the number of
+.I alias
+substititutions on a single line to 20.
+.SH "SEE ALSO"
+sh(1), newcsh(1), access(2), exec(2), fork(2), killpg(2), pipe(2), sigsys(2),
+umask(2), vlimit(2), wait(2), jobs(3), sigset(3), tty(4), a.out(5), environ(5),
+`An introduction to the C shell'
+.SH 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 internally.
+.PP
+Shell builtin functions are not stoppable/restartable.
+Command sequences of the form `a ; b ; c' are also not handled gracefully
+when stopping is attempted. If you suspend `b', the shell will then
+immediately execute `c'. This is especially noticeable if this
+expansion results from an
+.I alias.
+It suffices to place the sequence of commands in ()'s to force it to
+a subshell, i.e. `( a ; b ; c )'.
+.PP
+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.
+.PP
+Alias substitution is most often used to clumsily simulate shell procedures;
+shell procedures should be provided rather than aliases.
+.PP
+Commands within loops, prompted for by `?', are not placed in the
+.I history
+list.
+Control structure should be parsed rather than being recognized as built-in
+commands. This would allow control commands to be placed anywhere,
+to be combined with `|', and to be used with `&' and `;' metasyntax.
+.PP
+It should be possible to use the `:' modifiers on the output of command
+substitutions.
+All and more than one `:' modifier should be allowed on `$' substitutions.
projects / unix-history / commitdiff