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csh(1)									csh(1)

Name
       csh - C shell Command Interpreter

Syntax
       csh [-cefinstvVxX] [arg...]

Description
       The  command  is a command language interpreter that consists of a his‐
       tory mechanism, job control facilities, and  a  C-like  syntax.	 While
       this command has a set of built-in functions that it performs directly,
       the command line interpreter also reads and  translates	commands  that
       invokes	other  programs.   Additionally,  you can create shell scripts
       which the command can interpret.	 Shell scripts are files which contain
       executable instructions.

       The  percent  sign (%) represents the system prompt.  It indicates that
       you can begin entering commands to the system.  Each command line  that
       you  type  is  read  and	 broken into words.  This sequence of words is
       placed on a command history list and then parsed.  When the entire com‐
       mand  line  has	executed, the percent sign reappears and you can enter
       another command.	 See the History Substitution and  Jobs	 sections  for
       more information.

       To  use	the command's full job control facilities, you must invoke the
       tty driver described in This  driver  allows  generation	 of  interrupt
       characters  from	 the  keyboard	which  stop  execution	of a job.  For
       details on setting options in the tty driver, see

       Note that your environment setup is controlled by commands in the  home
       directory  of  your  .cshrc  file.  The command executes these commands
       when you enter the system.  Additionally, if this is a login shell, the
       Shell also executes the commands in your .login file.  These files usu‐
       ally contain your options for the tty driver and	 (terminal  settings).
       When a login shell session ends, commands are executed from the .logout
       file in your home directory.

Lexical Structure
       The shell splits input lines into words at blanks  and  tabs  with  the
       following exceptions:

       ·    ampersand (&)

       ·    bar ( | )

       ·    semicolon ( ; )

       ·    Left (<) and right (>) angle brackets

       ·    Left (() and right ()) parenthesis

       The  previous  metacharacters  form separate words.  If doubled as fol‐
       lows, these metacharacters form single words:

       ·    Doubled ampersand (&&)

       ·    Double bars (||)

       ·    Double left (<<) and right (>>) brackets

       ·    Backslash (\)

       ·    Single (` `) and double (" ") quotation marks.

       Metacharacters can be a part of other words.  Additionally, if  you  do
       not  want  a metacharacter to be interpreted as such by the system, you
       can precede it with a backslash e (\e).	A new line that is preceded by
       a is equivalent to a blank.

       Strings	enclosed  in single quotes (` `) or strings enclosed in double
       quotes (" ") form parts of a word.  Metacharacters  in  these  strings,
       including  blanks  and  tabs,  do  not  form  separate  words.  This is
       described in more detail later.	Within single quotes or double quotes,
       a new line preceded by a backslash (\) gives a true new line character.

       When the shell's input is not a terminal, the pound sign (#) introduces
       a comment which continues to the end of the input  line.	  It  is  pre‐
       vented this special meaning when preceded by a backslash (\) and single
       or double quotation marks.

Commands
       A command is a word or sequence of words that  directs  the  system  to
       perform a certain function.  You can separate commands with a bar ( | )
       which forms a pipeline.	The output that results from each  command  in
       the  pipeline  is  connected to the input of the next.  For example, in
       the following pipeline, a file is copied and the	 output	 is  piped  to
       standard output (the screen):
       % cp /example/dir/test . | more
       You  can form and execute several pipelines by separating each pipeline
       with a semicolon (;).  You can also force a command to complete	execu‐
       tion  in	 the  background  by typing an ampersand (&) at the end of the
       command line.

       You can form a simple command (which may be a component of  a  pipeline
       and  so on) by placing any of the above in parenthesis (()).  As in the
       C language, you can also separate pipelines with a double bar  (||)  or
       double  ampersands  (&&).  The double bar tells the command interpreter
       to execute the second command only if the  first	 command  fails.   The
       double  ampersands  tells the command interpreter to execute the second
       command if the first command is successful.

Jobs
       The Shell associates each command or pipeline with  a  job  index.   By
       typing  jobs  at	 the  system  prompt,  a  table of the current jobs is
       printed on your screen.	Each job listed has  a	small  integer	number
       associated  with	 it.   For  example, if you force a job into the back‐
       ground using an ampersand (&), the shell displays the  job  number  and
       process id of that job as follows:
       [1] 1234

       In  the previous example, the job number is 1 indicating that this is a
       background job and the process id is 1234.

       If you are running a job in the foreground, you can  suspend  execution
       of  that job by typing a CTRL/Z.	 The Shell then indicates that the job
       has been stopped and the system prompt reappears. If you type  jobs  at
       the prompt, the display indicates that a job has been stopped.  You can
       either enter another command at the prompt or you  can  manipulate  the
       state of the job you suspended as follows:

       ·    Place the job in background by using the bg command.

       ·    Continue  to execute the job by placing it in the foreground using
	    the fg command.

       A CTRL/Z takes effect immediately and is like an interrupt.  For	 exam‐
       ple,  pending output and unread output are discarded when the CTRL/Z is
       issued.	You can also type a CTRL/Y which does not generate a stop sig‐
       nal until a program attempts to perform a operation.

       If  a job that is being run in the background attempts to read from the
       terminal, it will stop.	Background jobs can produce output.   You  can
       prevent	background jobs from producing output by issuing the following
       command:
       stty tostop

       There are several ways to refer to jobs in the shell.  For example,  to
       bring  job  number 1 into the foreground, type %1 or fg %1.  Similarly,
       %1 & returns job 1 to the background.   If  a  job  does	 not  have  an
       ambiguous  prefix,  you can restart a job by it's prefix.  For example,
       %ex would restart a suspended job, if it is  the	 only  suspended  job.
       You use also use %?string which specifies a job whose command line con‐
       tains string.  Again, string cannot be an ambiguous name.

       The Shell tracks the current and previous jobs.	For example, in output
       displays	 of  jobs,  the current job is marked with a plus sign (+) and
       the previous job is marked with a minus sign (-).  Hence, you can  type
       %+ for the current job and %- for the previous job.  You can also spec‐
       ify %% which specifies the current job.

Status Reporting
       The Shell performs status reporting when	 the  process  state  changes.
       For  example,  if  a  job becomes blocked and further processing is not
       possible, the Shell informs you just before it prints  a	 prompt.   If,
       however, you set the Shell variable notify, the Shell provides you with
       immediate status of background jobs.  As opposed to  notifying  you  of
       all  changes  in	 background  jobs, the Shell command notify can mark a
       single process so that only its status change is reported.  To  mark  a
       single  file, type notify after starting a background job.  By default,
       only the current process is marked.

       If you try to exit from the Shell while jobs are stopped, the following
       warning appears:
       You have stopped jobs.

       You  can	 use the jobs command to view the stopped jobs. If you immedi‐
       ately try to exit again, the Shell does not provide  a  second  warning
       and suspended jobs are terminated.

Substitutions
       The  various  transformations  the  shell  performs on the input is now
       described in the order in which they occur.

History Substitutions
       History substitutions allow you to use words from previously typed com‐
       mands  as  portions  of	new commands.  This enables you to repeat com‐
       mands, arguments, or fix spelling mistakes from the previous command.

       An exclamation point (!) marks the beginning of a history substitution.
       It can appear anywhere in the input stream (including the beginning) as
       long as it is not nested.  An input line that contains history  substi‐
       tution is echoed to the screen before it is executed.

       The  exclamation	 point	(!)  may be preceded by a backslash (\) if you
       want to escape its special meaning.  If an exclamation  point  is  fol‐
       lowed  by  a  blank, tab, new line, equal sign (=), or left parenthesis
       ((), it is passed unchanged.

       Any command line that is typed at the terminal is saved on the  history
       list.  You can increase or decrease the size of your history list using
       the history variable; the previous command is always  retained  regard‐
       less  of its value.  Commands are numbered sequentially from 1. To dis‐
       play the history on your terminal, type history at the prompt  as  fol‐
       lows:
       % history

       This  command lists the commands that were previously typed.  For exam‐
       ple:
       1  write michael
       2  ex write.c
       3  cat oldwrite.c
       4  diff*write.c

       The commands are shown with their event numbers.	 Although  it  is  not
       usually necessary to use event numbers, you can reinvoke any command by
       combining the exclamation point (!) with any event number.   For	 exam‐
       ple, if you are referencing the previous history list, !4 reinvokes the
       command line diff*write.c.  You can also reinvoke a command without the
       event  number  as long as it is not ambiguous.  For example, !c invokes
       event 3 or !wri invokes event 1.	 The line !?mic? also refers to	 event
       1.  If you type !!, the last command entered in reinvoked.

       To  select  words  from an event, follow the event specification with a
       colon (:) 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, and so  forth.   The  basic  word
       designators are:

	    0	 first (command) word
	    n	 n'th argument
	    !	 first argument,  that is `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 colon (:) separating the event specification from the word designa‐
       tor can be omitted if the argument selector begins with a `!', `$', `*'
       `-'  or	`%'.   After  the  optional  word  designator  can be placed a
       sequence of modifiers, each preceded by a  colon	 (:).	The  following
       modifiers are defined:

	    h	   Remove a trailing pathname component, leaving the head.
	    r	   Remove a trailing `.xxx' component, leaving the root name.
	    e	   Remove all but the extension `.xxx' part.
	    s/l/r/ Substitute l for r
	    t	   Remove all leading pathname components, leaving the tail.
	    &	   Repeat the previous substitution.
	    g	   Apply the change globally, prefixing the above, for example, `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 new lines.

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

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

       A  special  abbreviation	 of  a history reference occurs when the first
       non-blank character of an input line is	a  circumflex  (^).   This  is
       equivalent  to  `!!:s/'	providing a convenient shorthand for substitu‐
       tions on the text of the previous  line.	  Thus	`^lb^lib^'  fixes  the
       spelling	 of  lb in the previous command.  Finally, a history substitu‐
       tion 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'.

       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  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, dis‐
       played, and modified by the alias and unalias commands.

       After the shell scans a command line, it parses the line into  distinct
       commands.  Then,	 the  shell  checks the first word of each command, in
       left-to-right order, to determine  if  the  command  line  contains  an
       alias.  When the shell finds an alias, it substitutes the definition of
       the alias for the alias in the command line. The shell reads the	 defi‐
       nition  of the alias using the history mechanism and treats the defini‐
       tion as if it was the previous input line.   If	the  alias  definition
       makes  no reference to the history list, the shell leaves the command's
       argument unchanged.

       For example, the following command creates an alias called ``ls:''
       % alias ls ´ls -l´
       After you issue this alias command, you receive information about files
       such  as their mode, number of links, owner, and so on when you use the
       ls alias.  For example, the following shows  the	 output	 from  the  ls
       alias created in the preceeding example:
       % ls usrsmithtext_file
       -rw-r--r--  1 smith	    21 Mar 12 11:53 text_file
       You  can	 also create aliases that allow you to supply arguments on the
       command line and arguments in the alias definition,  as	shown  in  the
       following example:
       % alias lookup ´grep \!^ /etc/passwd´
       You  must  specify  ``\'' before the ! to prevent the substitution from
       occurring in the alias command. The following shows the output from the
       lookup alias:
       % lookup smith
       smith:2vruqPosbG/bE:1321:10::usrsmith:bincsh
       The lookup alias finds and displays user Smith's entry in the file.

       You  can	 specify  an alias within an alias definition. After the shell
       finds an alias and substitutes its definition, it  searches  again  for
       aliases.	  The shell flags definitions that begin with the same word as
       the alias to prevent infinite loops. Other loops are detected and cause
       an error.

       You  can	 use  parser  metasyntax in an alias command. For example, the
       following is a valid command that creates the print alias:
       % alias print ´pr \!* | lpr´
       The print alias pipes output from the command to the command.

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
       which 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
       numeric calculations to be performed and the result assigned to a vari‐
       able.   Variable	 values	 are,  however, always represented as (zero or
       more) strings.  For the purposes of numeric operations, the null string
       is considered to be zero, and the second and subsequent words of multi‐
       word values are ignored.

       After the input line is aliased and parsed, and before each command  is
       executed,  variable  substitution is performed keyed by `$' characters.
       This expansion can be prevented by preceding the `$' with a `\'	except
       within  `"'s  where  it	always	occurs, and within `´'s where it never
       occurs.	Strings quoted by ``' are interpreted later (see Command  sub‐
       stitution  below) so `$' substitution does not occur there until later,
       if at all.  A `$' is passed unchanged if followed by a blank,  tab,  or
       end-of-line.

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

       Unless enclosed in `"' or given the `:q' modifier the results of	 vari‐
       able  substitution may eventually be command and file name 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  substitu‐
       tion  the  variable  will expand to multiple words with each word sepa‐
       rated by a blank and quoted to prevent later command or file name  sub‐
       stitution.

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

       $name
       ${name}
	    Are replaced by the words of the value of variable name, each sep‐
	    arated by a blank.	Braces insulate 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.
	    If	name  is  not a shell variable, but is set in the environment,
	    then that value is returned (but : modifiers and the  other	 forms
	    given below are not available in this case).

       $name[selector]
       ${name[selector]}
	    May	 be  used  to  select only some of the words from the value of
	    name.  The selector is subjected to `$' substitution and may  con‐
	    sist  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 mem‐
	    ber 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.

       $#name
       ${#name}
	    Gives the number of words in the variable.	 This  is  useful  for
	    later use in a `[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 `: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 colon (:) modifier
       on each `$' expansion."	The following substitutions may not  be	 modi‐
       fied with colon (:) modifiers.

       $?name
       ${?name}
	    Substitutes the string `1' if name is set, `0' if it is not.

       $?0
	    Substitutes `1' if the current input file name is known, `0' if it
	    is not.

       $$
	    Substitute the (decimal) process number of the (parent) shell.

       $<
	    Substitutes a line from the standard input, with no further inter‐
	    pretation thereafter.  It can be used to read from the keyboard in
	    a shell script.

Command And File Name Substitution
       The remaining substitutions, command and file  name  substitution,  are
       applied	selectively to the arguments of built-in 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.

Command Substitution
       Command substitution is indicated by a command enclosed	in  ``'.   The
       output  from  such  a command is normally broken into separate words at
       blanks, tabs and new lines, with null words being discarded, this  text
       then  replacing the original string.  Within `"'s, only new lines force
       new words; blanks and tabs are preserved.

       In any case, the single final new line 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.

File Name Substitution
       If a word contains any of the characters `*', `?', `[' or `{' or begins
       with  the  character  `~',  then that word is a candidate for file name
       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 file name
       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.

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

       The character `~' at the beginning of a file name is used to  refer  to
       home  directories.   Standing  alone,  that  is	`~', it expands to the
       invokers home directory as reflected in the value of the variable home.
       When  followed  by a name consisting of letters, digits and `-' charac‐
       ters 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 begin‐
       ning 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 sepa‐
       rately 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.

Input/output
       The  standard  input and 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 which is identical to word.
	    Word is not subjected to variable, file name or command  substitu‐
	    tion, and each input line is compared to word before any substitu‐
	    tions are done on this input line.	Unless a quoting `\', `"', `''
	    or	``'  appears in word variable and command substitution is per‐
	    formed on the intervening lines, allowing `\' to  quote  `$',  `\'
	    and	 ``'.	Commands  which are substituted have all blanks, tabs,
	    and new lines preserved, except for the final new  line  which  is
	    dropped.   The  resultant text is placed in an anonymous temporary
	    file which is given to the command as standard input.

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

	    If the variable noclobber is set, then the file must not exist  or
	    be	 a   character	special	 file  (for  example,  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.

	    The forms involving `&' route the diagnostic output into the spec‐
	    ified  file	 as  well as the standard output.  Name is expanded in
	    the same way as `<' input file names are.

       >> name
       >>& name
       >>! name
       >>&! name
	    Uses file name as 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 unless one of the `!' forms  is
	    given.  Otherwise similar to `>'.

       A  command  receives  the environment in which the shell was invoked as
       modified by the input-output parameters and the presence of the command
       in  a pipeline.	Thus, unlike some previous shells, commands run from a
       file of shell commands have no access to the text of  the  commands  by
       default;	 rather they receive the original standard input of the shell.
       The `<<' mechanism should be used to present inline data.  This permits
       shell command scripts to function as components of pipelines and allows
       the shell to block read its input.   Note  that	the  default  standard
       input  for  a command run detached is not 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 Jobs above.)

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

Expressions
       A number of the built-in 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  @,  exit,  if,  and
       while commands.	The following operators are available:

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

       Here the precedence increases to the right, `==' `!='  `=~'  and	 `!~',
       `<='  `>='  `<'	and  `>',  `<<' and `>>', `+' and `-', `*' `/' and `%'
       being, in groups, at the same level.  The `==' `!=' `=~' and `!~' oper‐
       ators  compare  their  arguments as strings; all others operate on num‐
       bers.  The operators `=~' and `!~' are like `!=' and `=='  except  that
       the  right  hand side is a pattern (containing, for example, `*'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 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  syntacti‐
       cally  significant  to the parser (`&' `|' `<' `>' `(' `)') 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

       The specified name is command and file name 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, that
       is  `0'.	  Command  executions succeed, returning true, that is `1', if
       the command exits with status 0, otherwise they fail, returning	false,
       that  is `0'.  If more detailed status information is required then the
       command should be executed outside of an expression  and	 the  variable
       status examined.

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 imple‐
       mentation, 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
       single simple command on an input line as shown below.

       If  the shell's input is not seekable, the shell buffers up input when‐
       ever a loop is being read and performs seeks in this internal buffer to
       accomplish the rereading implied by the loop.  (To the extent that this
       allows, backward 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 exe‐
       cuted in a subshell.

       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 file name  substituted.
	    Name is not allowed to be alias or unalias.

       alloc
	    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 produc‐
	    tion versions of the shell; it requires a modified version of  the
	    system memory allocator.

       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  enclosing
	    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 begins with `/', then this is tried to see if it is  a
	    directory.

       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 new line unless the -n
	    option is specified.

       else
       end
       endif
       endsw
	    See the description of the foreach, if, switch, and	 while	state‐
	    ments 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 commands generated as the result
	    of command or variable substitution, since parsing	occurs	before
	    these substitutions.  See 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 variable
	    (first form) or with the  value  of	 the  specified	 expr  (second
	    form).

       fg
       fg %job ...
	    Brings the current or specified jobs into the foreground, continu‐
	    ing 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 sep‐
	    arate lines.)

	    The	 built-in  command  continue  may be used to continue the loop
	    prematurely and the built-in command break to terminate it	prema‐
	    turely.   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 ter‐
	    minal you can rub it out.

       glob wordlist
	    Like echo but no `\' escapes are recognized and words  are	delim‐
	    ited  by null characters in the output.  Useful for programs which
	    wish to use the shell to file name expand a list of words.

       goto word
	    The specified word is file name 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 speci‐
	    fied line.

       hashstat
	    Print a statistics line indicating 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 which
	    does not begin with a `/'.

       history
       history n
       history -r n
       history -h n
	    Displays the history event list; if n is given  only  the  n  most
	    recent  events  are	 printed.  The -r option reverses the order of
	    printout to be most recent first rather than oldest first.	The -h
	    option  causes the history list to be printed without leading num‐
	    bers.  This is used to produce files suitable for  sourcing	 using
	    the -h option to source.

       if (expr) command
	    If	the  specified expression evaluates true, then the single com‐
	    mand with arguments is executed.  Variable substitution 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 com‐
	    mand  list,	 or  a parenthesized command list.  Input/output redi‐
	    rection occurs even if expr is false, 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 to the first else
	    are executed; else if expr2 is true then the commands to the  sec‐
	    ond	 else are executed, etc.  Any number of else-if pairs are pos‐
	    sible; 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; given the -l options lists process id's in
	    addition to the normal information.

       kill %job
       kill -sig %job ...
       kill pid
       kill -sig pid ...
       kill -l
	    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 /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	 (con‐
	    tinue) signal as well.

       limit
       limit resource
       limit 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.

	    The following resources can be controlled:

       ·    cputime (maximum number of cpu-seconds to be used by each process)

       ·    filesize (largest single file which can be created)

       ·    datasize (the maximum growth of the data+stack  region  by	beyond
	    the end of the program text)

       ·    stacksize  (the  maximum  size of the automatically-extended stack
	    region)

       ·    coredumpsize (the size of the largest core dump that can  be  cre‐
	    ated).

       ·    memoryuse  (the maximum amount of main memory a process is allowed
	    to occupy)

	    The maximum-use may be given as a (floating point or integer) num‐
	    ber followed by a scale factor.  For all limits other than cputime
	    the default scale is `k' or `kilobytes' (1024 bytes); a scale fac‐
	    tor	 of  `m'  or  `megabytes'  may	also be used.  For 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.

	    For both resource names and scale factors, unambiguous prefixes of
	    the names suffice.

       login
	    Terminate  a  login	 shell,	 replacing  it	with  an  instance  of
	    /bin/login.	 This is one way to log off, included for  compatibil‐
	    ity with

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

       nice
       nice +number
       nice command
       nice +number command
	    The first form sets the nice for this shell to 4.  The second form
	    sets the nice to the given number.	The final two forms  run  com‐
	    mand  at  priority	4 and 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 com‐
	    mands 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  pro‐
	    cesses detached with `&' are effectively nohup'ed.

       notify
       notify %job ...
	    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 vari‐
	    able 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 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.

	    In any case, if the shell is running detached and  interrupts  are
	    being  ignored, all forms of onintr have no meaning and interrupts
	    continue to be ignored by the shell and all invoked commands.

       popd
       popd +n
	    Pops the directory stack, returning	 to  the  new  top  directory.
	    With  a  argument  `+n'  discards the nth entry in the stack.  The
	    elements of the directory stack are numbered from  0  starting  at
	    the top.

       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  (using and pushes the old current working directory (as
	    in csw) onto  the  directory  stack.   With	 a  numeric  argument,
	    rotates  the  nth 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.

       rehash
	    Causes  the internal hash table of the contents of the directories
	    in the path variable to be recomputed.  This is needed if new com‐
	    mands  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 con‐
	    tents of one of the system directories.

       repeat count command
	    The specified command which is subject to the same restrictions as
	    the	 command in the one line if statement above, is executed count
	    times.  I/O redirections occur exactly 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	 vari‐
	    ables.   Variables	which  have  other than a single word as 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  exist.   The final form sets name to the
	    list of words in wordlist.	In all cases the value is command  and
	    file name expanded.

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

       setenv name value
	    Sets  the value of environment variable name to be value, a single
	    string.  The most commonly used environment variable  USER,	 TERM,
	    and PATH are automatically imported to and exported from the vari‐
	    ables 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 during source commands
	    is not placed on the history list; the -h option causes  the  com‐
	    mands to be placed in the history list without being executed.

       stop
       stop %job ...
	    Stops the current or specified job which is executing in the back‐
	    ground.

       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

       switch (string)
       case str1:
	   ...
	 breaksw
       ...
       default:
	   ...
	 breaksw
       endsw
	    Each case label is successively  matched,  against	the  specified
	    string  which  is  first command and file name 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  breaksw	causes
	    execution to continue after the 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
	    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 specified simple
	    command is timed and a time summary as described  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.  Com‐
	    mon 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.

       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 executed  pro‐
	    grams is disabled.

       unlimit resource
       unlimit
	    Removes  the limitation on resource.  If no resource is specified,
	    then all resource limitations are removed.

       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 error for  nothing	to  be
	    unset.

       unsetenv pattern
	    Removes  all variables whose name match the specified pattern from
	    the environment.  See also the setenv command above and

       wait
	    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.

       while (expr)
	   ...
       end
	    While the specified expression evaluates  non-zero,	 the  commands
	    between  the  while and the matching end are evaluated.  Break and
	    continue may be used to terminate  or  continue  the  loop	prema‐
	    turely.   (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 variables.  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, that is `@  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 this is done
       explicitly by the user.

       This shell copies the environment variable USER into the variable user,
       TERM  into  term,  and  HOME  into home, and copies these back into the
       environment whenever the normal shell variables are reset.   The	 envi‐
       ronment	variable  PATH	is  likewise  handled.	It is not necessary to
       worry about its setting other than in the file  as  inferior  processes
       will  import 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 vari‐
		      able that positional parameters are substituted, that is
		      `$1' is replaced by `$argv[1]', and so forth.

       cdpath	      Gives a list of alternate directories searched  to  find
		      subdirectories 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  executed.	  For non-built-in commands all expan‐
		      sions  occur  before  echoing.   Built-in	 commands  are
		      echoed  before command and file name substitution, since
		      these substitutions are then done selectively.

       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 default character !.  The second character
		      of its value replaces the character ! in quick substitu‐
		      tions.

       history	      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 val‐
		      ues of history may run the shell	out  of	 memory.   The
		      last  executed  command  is  always saved on the history
		      list.

       home	      The home directory of the invoker, initialized from  the
		      environment.   The  file name expansion of `~' refers to
		      this variable.

       ignoreeof      If set the shell ignores end-of-file from input  devices
		      which are terminals.  This prevents shells from acciden‐
		      tally being killed by control-D's.

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

		      If the first word of the value of	 mail  is  numeric  it
		      specifies	 a  different  mail checking interval, in sec‐
		      onds, than the default, 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,  restric‐
		      tions  are  placed  on output redirection to insure that
		      files are not  accidentally  destroyed,  and  that  `>>'
		      redirections refer to existing files.

       noglob	      If  set, file name expansion is inhibited.  This is most
		      useful in shell scripts which are not dealing with  file
		      names,  or  after a list of file names has been obtained
		      and further expansions are not desirable.

       nonomatch      If set, it is not an error for a file name expansion  to
		      not  match any existing files; rather the primitive pat‐
		      tern is returned.	 It is still an error for  the	primi‐
		      tive  pattern  to	 be  malformed, that is `echo [' still
		      gives an error.

       notify	      If set, the shell notifies asynchronously of job comple‐
		      tions.  The default is to rather 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 specifies the current directory.  If	 there	is  no
		      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 -c nor
		      the -t option will normally hash	the  contents  of  the
		      directories  in the path variable after reading 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 give the rehash or the commands  may
		      not be found.

       prompt	      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 num‐
		      ber unless a preceding `\' is given.  Default is	`%  ',
		      or `# ' for the super-user.

       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 which has been ref‐
		      erenced 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.

       shell	      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 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 termi‐
		      nated abnormally, then 0200  is  added  to  the  status.
		      Built-in commands which fail return exit status `1', all
		      other built-in commands set status `0'.

       time	      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	termi‐
		      nates.   The time command can be used to cause a command
		      to be timed no matter how much CPU time it takes.	 Thus
		      % time cp /etc/rc /usr/bill/rc
		      0.0u 0.1s 0:01 8% 2+1k 3+2io 1pf+0w
		      % time wc /etc/rc /usr/bill/rc
			52   178  1347 /etc/rc
			52   178  1347 /usr/bill/rc
			104  356  2694 total
		      0.1u 0.1s 0:00 13% 3+3k 5+3io 7pf+0w
		      %
		      The preceding example indicates that the cp command used
		      a negligible amount of user time (u) and about 1/10th of
		      a second system time (s); the elapsed time was 1	second
		      (0:01), there was an average memory usage of 2k bytes of
		      program space and 1k bytes of data space	over  the  cpu
		      time  involved  (2+1k); the program did three disk reads
		      and two disk writes (3+2io), and took one page fault and
		      was not swapped (1pf+0w).	 The word count command on the
		      other hand used 0.1 seconds of user time and 0.1 seconds
		      of  system  time	in less than a second of elapsed time.
		      The percentage `13%' indicates that over the period when
		      it  was  active  the  command `wc' used an average of 13
		      percent of the available CPU cycles of the machine.

       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 Each  word  in	 the  variable
       path names a directory from which the shell will attempt to execute 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	greatly speeds command location when a
       large number of directories are present in the search  path.   If  this
       mechanism has been turned off (via unhash), or if the shell was given a
       -c or -t argument, and in any case for each directory component of 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.

       Parenthesized  commands are always executed in a subshell.  Thus `(cd ;
       pwd) ; pwd' prints the home  directory;	leaving	 you  where  you  were
       (printing  this	after the home directory), while `cd ; pwd' leaves you
       in the home directory.  Parenthesized commands are most often  used  to
       prevent 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 (for exam‐
       ple, `$shell').	Note that this is a special, late occurring,  case  of
       alias  substitution, and only allows words to be prepended to the argu‐
       ment list without modification.

Argument List Processing
       If argument 0 to the shell is `-' then this is a login shell.  The flag
       arguments are interpreted as follows:

       -c   The	 first	argument  word	is  taken to be a command string.  All
	    remaining argument words 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	invokers  home
	    directory.

       -i   The shell is interactive and prompts for its top-level input, even
	    if stdin appears not to be a  terminal.   Shells  are  interactive
	    without this option if their inputs and outputs are terminals.

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

       -s   Command input is taken from the standard input.

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

       -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, so that commands are echoed
	    immediately before execution.

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

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

       After  processing of flag arguments if arguments remain but none of the
       -c, -i, -s, or -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  exe‐
       cute  such a `standard' shell if the first character of a script is not
       a `#', that is if the script does not start with a comment.   Remaining
       arguments initialize the variable argv.

Signal Handling
       The shell normally ignores quit signals.	 Jobs running detached (either
       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  shells  handling  of
       interrupts  and terminate signals in shell scripts can be controlled by
       onintr.	Login shells catch the 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'.

Command And Filename Recognition
       The  command  recognizes	 and  completes	 user  name  aliases, commands
       (including built-in commands), and filenames.  To use this feature,  do
       the following:

       1. Type	enough characters at the prompt to make your input to the sys‐
	  tem unique.

       2. Press the ESC key.

       If your input is unique, the Shell completes the input  line.   If  the
       input  is  not  unique,	the  terminal signals you with a beep.	If you
       receive a beep, type CTRL/D for a list of options.  You can  then  type
       the  additional	characters that will make your text unique.  After you
       have provided more input, press the ESC key again.

Command Line Editing
       The command allows you to visually edit command lines using either a or
       environment.  The interface is modal and supports a subset of commands.
       The interface is modeless and supports a subset of commands.   See  the
       Editing Interface section for a list of the available and commands.

       To  set	the editing environment, define the Shell environment variable
       CSHEDIT as or If the environment variable CSHEDIT is not	 defined,  the
       command	searches for your EDITOR environment variable.	When your EDI‐
       TOR environment variable is set to or the command defaults to the  com‐
       mand  interface.	  If  your EDITOR environment is not set to any of the
       previously mentioned editors, the default  is  the  command  interface.
       Note  that  if  neither the CSHEDIT or EDITOR environment variables are
       defined, the command defaults to the command interface.

       The new history modifier (:v) allows you to pull commands from the his‐
       tory  list to make them available for editing in visual edit mode.  The
       symbol :v tells the Shell that you want to enter visual edit mode.  For
       example,	 the  following	 command line invokes edit mode for the previ‐
       ously typed command line:
       !cp:v
       When you press the ESC key as the first character on a command line, it
       is equivalent to typing the following:
       !!:v
       Thus,  the  previous example invokes edit mode for the last command you
       entered.

       Another useful editing feature is scrolling through the	history	 list.
       After you have entered edit mode by typing either !command:v or the ESC
       key, you can use the up-arrow and down-arrow keys to scroll through the
       history list and you may edit any command line in that history list.

       When  you  are  in edit mode, all control characters are displayed as a
       space character.	 Additional control  characters	 cannot	 be  inserted.
       Existing control characters are preserved.

Editing Interface
       The available commands follow:

       h	      Move left one character (r).

       l	      Move right one character (r).

       0	      Move to the start of the line.

       $	      Move to the end of the line.

       w	      move forward one word (r).

       b	      Move back one word (r).

       e	      Move to end of word (r).

       fx	      Move forward onto character (r).

       Fx	      Move back onto character (r).

       tx	      Move forward up to character (r).

       Tx	      Move back up to character (r).

       %	      Move to matching bracket ({[]}).

       i	      Insert text before cursor.

       I	      Insert text at beginning of line.

       a	      Append text after cursor.

       A	      Append text at end of line.

       c	      Change text (o).

       C	      Change to end of line (eol) (c$).

       <esc>	      End insertion.

       x	      Delete char under cursor (r).

       X	      Delete character before cursor (r).

       r	      Replace a character (r).

       ~	      Change case of current character (r).

       d	      Delete text (o).

       D	      Delete to eol (d$).

       u	      Undo last change.

       U	      Undo all changes.

       .	      Repeat last text change command (r).

       p	      Put text from previous delete after cursor (r).

       P	      Put text from previous delete before cursor (r).

       ^L,^R	      Redraw command line.

       /word	      Search  back through the history list for a command con‐
		      taining the specified word.  If the  specified  word  is
		      not  delineated  by white space in the history list, the
		      search fails.  Typing ESCAPE or CTRL/C aborts this  com‐
		      mand.

       n	      Repeat last history search.

       <RETURN>	      End edit and execute command.

       ^C	      Quit; no command executed.

       (r)	      A repeat count is accepted.

       (o)	      Works within a cursor motion object.

       The available commands follow:

       ^@	      Set mark (keyword null).

       ^A	      Move to beginning of line.

       ^B,	      Move backward a character.

       ^C	      Exit command line edit; do not execute a command.

       ^D	      Delete next character (to kill buffer).

       ^E	      Move to end of line.

       ^F,	      Move forward a character.

       ^G	      Cancel partial command.

       ^H,DEL	      Delete previous character (to kill buffer).

       ^K	      Kill (delete) to end of line (to kill buffer).

       ^L	      Redraw line display.

       ^R	      Search reverse for a single character.

       ^S	      Search forward for a single character.

       ^T	      Transpose two characters before cursor.

       ^Un	      Specify  a  repeat count before command (default of n is
		      4).

       ^W	      Delete between cursor and mark (to kill buffer).

       ^Y	      Yank from kill buffer.

       CR,NL	      End edit and execute command.

       ESC-^C	      End edit and execute command.

       ESC-B	      Move backward a word.

       ESC-D	      Delete next word.

       ESC-F	      Move forward a word.

       ESC-H	      Delete previous word.

       ESC-DEL	      Delete previous word.

       ESC-n	      Repeat count before command.

       ^X^C	      End edit and execute command.

       ^Xu	      Undo last change.

       ^XU	      Undo all changes.

       ^X~	      Change case of next character.

       ^X^Sword	      Search back through the history list for a command  con‐
		      taining  a specified word.  If the specified word is not
		      delineated by white  space  in  the  history  list,  the
		      search fails.  Typing  ESCAPE or CTRL/C aborts this com‐
		      mand.

       ^X^S	      Repeat last history search  command.   You  must	be  in
		      search mode to issue this command.  Note that ^G cancels
		      the previous search word so that you  can	 enter	a  new
		      word.

Restrictions
       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 file name 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  alias  substitu‐
       tions on a single line to 20.

       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 (that is, wrong) as the job may have changed directories
       internally.

       Shell  built-in	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 immedi‐
       ately  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 subshell, that is `( a ; b ; c )'.

       Commands	 within loops, prompted for by `?', are not placed in the his‐
       tory list.  Control structure should be parsed rather than being recog‐
       nized  as  built-in  commands.  This would allow control commands to be
       placed anywhere, to be combined with `|', and to be used with  `&'  and
       `;' metasyntax.

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

       Symbolic	 links	fool the shell.	 In particular, dirs and `cd ..' don't
       work properly once you've crossed through a symbolic link.

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), time(1),	access(2),  execve(2),	fork(2),  killpg(2),  pipe(2),
       sigvec(2),  setrlimit(2),  umask(2),  wait(2),  tty(4), a.out(5), envi‐
       ron(7), time(7)
       "An Introduction to the C shell", Supplementary	Documents,  Volume  1:
       General User

									csh(1)
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