HPUX csh[1]
csh(1) csh(1)
NAME
csh - a shell (command interpreter) with C-like syntax
SYNOPSIS
csh [-cefinstvxTVX] [command_file] [argument_list ...]
DESCRIPTION
csh is a command language interpreter that incorporates a command
history buffer, C-like syntax, and job control facilities.
Command Options
Command options are interpreted as follows:
-c Read commands from the (single) following argument
which must be present. Any remaining arguments are
placed in argv.
-e C shell exits if any invoked command terminates
abnormally or yields a non-zero exit status.
-f Suppress execution of the .cshrc file in your home
directory, thus speeding up shell start-up time.
-i Force csh to respond interactively when called from a
device other than a computer terminal (such as another
computer). csh normally responds non-interactively.
If csh is called from a computer terminal, it always
responds interactively, regardless of which options are
selected.
-n Parse but do not execute commands. This is useful for
checking syntax in shell scripts. All substitutions
are performed (history, command, alias, etc.).
-s Take command input from the standard input.
-t Read and execute a single line of input.
-v Set the verbose shell variable, causing command input
to be echoed to the standard output device after
history substitutions are made.
-x Set the echo shell variable, causing all commands to be
echoed to the standard error immediately before
execution.
-T Disable the tenex features which use the ESC key for
command/file name completion and CTRL-D for listing
available files (see the CSH UTILITIES section below)
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-V Set the verbose variable before .cshrc is executed so
that all .cshrc commands are also echoed to the
standard output.
-X Set the echo variable before .cshrc is executed so that
all .cshrc commands are also echoed to the standard
output.
After processing the command options, if arguments remain in the
argument list, and the -c, -i, -s, or -t options were not specified,
the first remaining argument is taken as the name of a file of
commands to be executed.
COMMANDS
A simple command is a sequence of words, the first of which specifies
the command to be executed. A sequence of simple commands separated
by vertical bar (|) characters forms a pipeline. The output of each
command in a pipeline becomes the input for the next command in the
pipeline. Sequences of pipelines can be separated by semicolons (;)
which causes them to be executed sequentially. A sequence of
pipelines can be executed in background mode by adding an ampersand
character (&) after the last entry.
Any pipeline can be placed in parentheses to form a simple command
which, in turn, can be a component of another pipeline. Pipelines can
also be separated by || or && indicating, as in the C language, that
the second pipeline is to be executed only if the first fails or
succeeds, respectively.
Jobs
csh associates a job with each pipeline and keeps a table of current
jobs (printed by the jobs command) and assigns them small integer
numbers. When a job is started asynchronously using &, the shell
prints a line resembling:
[1] 1234
indicating that the job which was started asynchronously was job
number 1 and had one (top-level) process, whose process id was 1234.
If you are running a job and want to do something else, you can type
the currently defined suspend character (see termio(7)) which sends a
stop signal to the current job. csh then normally indicates that the
job has been `Stopped', and prints another prompt. You can then
manipulate the state of this job, putting it in the background with
the bg command, run some other commands, and then eventually bring the
job back into the foreground with the foreground command fg. A
suspend takes effect immediately and is like an interrupt in that
pending output and unread input are discarded when it is typed. There
is a delayed suspend character which does not generate a stop signal
until a program attempts to read(2) it. This can usefully be typed
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ahead when you have prepared some commands for a job which you want to
stop after it has read them.
A job being run in the background stops if it tries to read from the
terminal. Background jobs are normally allowed to produce output, but
this can be disabled by giving the command stty tostop (see stty(1)).
If you set this tty option, background jobs stop when they try to
produce output, just as they do when they try to read input. Keyboard
signals and line-hangup signals from the terminal interface are not
sent to background jobs on such systems. This means that background
jobs are immune to the effects of logging out or typing the interrupt,
quit, suspend, and delayed suspend characters (see termio(7)).
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, typing %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 normally restarts a suspended ex(1)
job, if there is only one suspended job whose name begins with the
string ex. It is also possible to say %?string which specifies a job
whose text contains string, if there is only one such job.
csh 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 history mechanism (described below), %% is also a synonym for
the current job.
csh 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 printing a prompt. This is done so
that it does not otherwise disturb your work. If, however, you set
the shell variable notify, csh notifies you immediately of changes in
status of background jobs. There is also a csh built-in command
called notify which marks a single process so that any status change
is immediately reported. By default, notify marks the current
process. Simply type notify after starting a background job to mark
it.
If you try to leave the shell while jobs are stopped, csh sends the
warning message: You have stopped jobs. Use the jobs command to see
what they are. If you do this or immediately try to exit again, csh
does not warn you a second time, and the suspended jobs are terminated
(see exit(2)).
Built-In Commands
Built-in commands are executed within the shell without spawning a new
process. If a built-in command occurs as any component of a pipeline
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except the last, it is executed in a subshell. The built-in commands
are:
alias
alias name
alias name wordlist
The first form prints all aliases. The second form
prints the alias for name. The third form assigns the
specified wordlist as the alias of name. Command and
file name substitution are performed on wordlist. name
cannot be alias or unalias.
bg [%job ...]
Put the current (job not specified) 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 directory_name
chdir
chdir directory_name
Change the shell's current working directory to
directory_name. If not specified, directory_name
defaults to your home directory.
If directory_name is not found as a subdirectory of the
current working directory (and does not begin with /, ./,
or ../), each component of the variable cdpath is checked
to see if it has a subdirectory directory_name. Finally,
if all else fails, csh treats directory_name as a shell
variable. If its value begins with /, 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 other case labels.
dirs Prints the directory stack; the top of the stack is at
the left; the first directory in the stack is the current
directory.
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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 descriptions of the foreach, if, switch, and
while statements below.
eval arguments ...
(Same behavior as sh(1).) 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.
exec command
The specified command is executed in place of the current
shell.
exit
exit (expression)
csh exits either with the value of the status variable
(first form) or with the value of the specified
expression (second form).
fg [%job ...]
Brings the current (job not specified) or specified jobs
into the foreground, continuing them if they were
stopped.
foreach name (wordlist)
...
end The variable name is successively set to each member of
wordlist and the sequence of commands between this
command and the matching end are executed. (Both foreach
and end must appear alone on separate lines.)
The built-in command continue can be used to continue the
loop prematurely; the built-in command break to terminate
it prematurely. When this command is read from the
terminal, the loop is read once, prompting with ? before
any statements in the loop are executed. If you make a
mistake while typing in a loop at the terminal, use the
erase or line-kill character as appropriate to recover.
glob wordlist
Like echo but no \ escapes are recognized and words are
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delimited by null characters in the output. Useful in
programs that use the shell to perform file name
expansion on 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 specified line.
hashstat
Print a statistics line indicating how effective the
internal hash table has been at locating commands (and
avoiding execs). An exec is attempted for each component
of the path where the hash function indicates a possible
hit, and in each component that does not begin with a /.
history [-h] [-r] [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 prints the history list
without leading numbers for producing files suitable for
the source command.
if (expression) command
If expression evaluates true, the single command 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 command list, a parenthesized command list,
or an aliased command. Input/output redirection occurs
even if expression is false, meaning that command is not
executed (this is a bug).
if (expression1) then
...
else if (expression2) then
...
else
...
endif If expression1 is true, all commands down to the first
else are executed; otherwise if expression2 is true, all
commands from the first else down to the second else are
executed, etc. Any number of else-if pairs are possible,
but 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.)
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jobs [-l]
Lists active jobs. The -l option lists process IDs in
addition to the usual 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 SIG prefix (see
signal(2)). The signal names are listed by kill -l.
There is no default, so kill used alone does not send a
signal to the current job. If the signal being sent is
TERM (terminate) or HUP (hangup), the job or process is
sent a CONT (continue) signal as well.
login Terminates a login shell, replacing it with an instance
of /bin/login. This is one way to log off, included for
compatibility with sh(1).
logout Terminates a login shell. Especially useful if ignoreeof
is set. A similar function, bye, which works for
sessions that are not login shells, is provided for
historical reasons. Its use is not recommended because
it is not part of the standard BSD csh and may not be
supported in future releases.
newgrp Changes the group identification of the caller; for
details see newgrp(1). A new shell is executed by newgrp
so that the current shell environment is lost.
nice
nice +number
nice command
nice +number command
The first form sets the nice (run command priority) for
this shell to 4 (the default). The second form sets the
priority to the given number. The final two forms run
command at priority 4 and number respectively. The user
with appropriate privileges can raise the priority by
specifying negative niceness using nice -number ...
command is always executed in a sub-shell, and
restrictions placed on commands in simple if statements
apply.
nohup [command]
Without an argument, nohup can be used in shell scripts
to cause hangups to be ignored for the remainder of the
script. With an argument, causes the specified command
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to be run with hangups ignored. All processes executed
in the background with & are effectively nohuped as
described under Jobs in the COMMANDS section.
notify [job ...]
Causes the shell to notify the user asynchronously when
the status of the current (job not specified) or
specified jobs changes; normally notification is
presented before a prompt. This is automatic if the
shell variable notify is set.
onintr [-] [label]
Controls the action of the shell on interrupts. With no
arguments, onintr restores the default action of the
shell on interrupts, which action is to terminate shell
scripts or return to the terminal command input level.
If - is specified, all interrupts are ignored. If a
label is given, the shell executes a goto label when an
interrupt is received or a child process terminates
because it was interrupted.
If the shell is running in the background and interrupts
are being ignored, onintr has no effect; interrupts
continue to be ignored by the shell and all invoked
commands.
popd [+n]
Pops the directory stack, returning to the new top
directory. With an argument, discards the nth entry in
the stack. The elements of the directory stack are
numbered from 0 starting at the top. A synonym for popd,
called rd, is provided for historical reasons. Its use
is not recommended because it is not part of the standard
BSD csh and may not be supported in future releases.
pushd [name] [+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 cd) and pushes the
old current working directory (as in csw) onto the
directory stack. With a numeric argument, pushd rotates
the nth argument of the directory stack around to be the
top element and changes to that directory. The members
of the directory stack are numbered from the top starting
at 0. A synonym for pushd, called gd, is provided for
historical reasons. Its use is not recommended since it
is not part of the standard BSD csh and may not be
supported in future releases.
rehash Causes the internal hash table of the contents of the
directories in the path variable to be recomputed. This
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is needed if new commands are added to directories in the
path while you are logged in. This should only be
necessary if you add commands to one of your own
directories or if a systems programmer changes the
contents of 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 set shows the value of all shell
variables. Variables whose value is other than a single
word 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 indexth
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 can 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
variables, USER, TERM, and PATH, are automatically
imported to and exported from the csh variables user,
term, and path; there is no need to use setenv for these.
shift [variable]
If no argument is given, the members of argv are shifted
to the left, discarding argv[1]. An error occurs if argv
is not set or has less than two strings assigned to it.
When variable is specified, shift performs the same
function on the specified variable.
source [-h] name
csh reads commands from name. source commands can be
nested, but if 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
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during source commands is not placed on the history list.
The -h option can be used to place commands in the
history list without being executing them.
stop [%job ...]
Stops the current (no argument) or specified jobs
executing in the background.
suspend Causes csh to stop as if it had been sent a suspend
signal. Since csh normally ignores suspend signals, this
is the only way to suspend the shell. This command gives
an error message if attempted from a login shell.
switch (string)
case str1:
...
breaksw
...
default:
...
breaksw
endsw Each case label (str1) is successively matched against
the specified string which is first command and file name
expanded. The form of the case labels is the Pattern
Matching Notation with the exception that non-matching
lists in bracket expressions are not supported (see
regexp(5)). If none of the labels match before a default
label is found, the execution begins after the default
label. Each case label and the default label must appear
at the beginning of a line. The breaksw command 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 [command]
When command is not specified, a summary of time used by
this shell and its children is printed. If specified,
the 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 [value]
The current file creation mask is displayed (value not
specified) or set to the specified value. The mask is
given in octal. Common values for the mask are 002,
which gives all permissions to the owner and group and
read and execute permissions to all others, or 022, which
gives all permissions to the owner, and only read and
execute permission to the group and all others.
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unalias pattern
All aliases whose names match the specified pattern are
discarded. Thus, all aliases are removed by unalias *.
No error occurs if pattern does not match an existing
alias.
unhash Use of the internal hash table to speed location of
executed programs is disabled.
unset pattern
All variables whose names match the specified pattern are
removed. Thus, all variables are removed by unset *;
this has noticeably undesirable side-effects. No error
occurs if pattern matches nothing.
unsetenv pattern
Removes all variables whose names match the specified
pattern from the environment. See also the setenv
command above and printenv(1).
wait Waits for all background jobs to terminate. If the shell
is interactive, an interrupt can disrupt the wait, at
which time the shell prints names and job numbers of all
jobs known to be outstanding.
while (expression)
...
end While the specified expression evaluates non-zero, the
commands between the while and the matching end are
evaluated. break and continue can be used to terminate
or continue the loop prematurely. (The while and end
must appear alone on their input lines.) If the input is
a terminal (i.e., not a script), prompting occurs the
first time through the loop as for the foreach statement.
%job Brings the specified job into the foreground.
%job & Continues the specified job in the background.
@
@ name=expression
@ name[index]=expression
The first form prints the values of all the shell
variables. The second form sets the specified name to
the value of expression. If the expression contains <,
>, &, or |, at least this part of the expression must be
placed within parentheses. The third form assigns the
value of expression to the indexth argument of name.
Both name and its indexth component must already exist.
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The operators *=, +=, etc., are available as in C. White
space can optionally separate the name from the
assignment operator. However, spaces are mandatory in
separating components of expression which would otherwise
be single words.
Special postfix ++ and -- operators increment and
decrement name, respectively (e.g., @ i++).
Non-Built-In Command Execution
When a command to be executed is not a built-in command, csh attempts
to execute the command via exec(2). Each word in the variable path
names a directory in which the shell attempts to find the command (if
the command does not begin with /). If neither -c nor -t is given,
the shell hashes the names in these directories into an internal table
so that an exec is attempted only in those directories where the
command might possibly reside. 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 -c or -t was
given, or if any directory component of path does not begin with a /,
the shell concatenates the directory name and the given command name
to form a path name of a file which it then attempts to execute.
Commands placed inside parentheses are always executed in a subshell.
Thus
(cd ; pwd)
prints the home directory then returns to the current directory upon
completion, whereas:
cd ; pwd
remains in the home directory upon completion.
When commands are placed inside parentheses, it is usually to prevent
chdir from affecting the current shell.
If the file has execute permissions but is not an executable binary
file, it is assumed to be a script file, which is a file of data for
an interpreter that is executed as a separate process.
csh first attempts to load and execute the script file (see exec(2)).
If the first two characters of the script file are #!, exec(2) expects
an interpreter path name to follow and attempts to execute the
specified interpreter as a separate process to read the entire script
file.
If no #! interpreter is named, and there is an alias for the shell,
the words of the alias are inserted at the beginning of the argument
list to form the shell command. The first word of the alias should be
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the full path name of the command to be used. Note that this is a
special, late-occurring case of alias substitution, which inserts
words into the argument list without modification.
If no #! interpreter is named and there is no shell alias, but the
first character of the file is #, the interpreter named by the $shell
variable is executed (note that this normally would be /bin/csh,
unless the user has reset $shell). If $shell is not set, /bin/csh is
executed.
If no !# interpreter is named, and there is no shell alias, and the
first character of the file is not #, /bin/sh is executed to interpret
the script file.
History Substitutions
History substitutions enable you to repeat commands, use words from
previous commands as portions of new commands, repeat arguments of a
previous command in the current command, and fix spelling or typing
mistakes in an earlier command.
History substitutions begin with an exclamation point (!).
Substitutions can begin anywhere in the input stream, but cannot be
nested. The exclamation point can be preceded by a backslash to
cancel its special meaning. For convenience, an exclamation point is
passed to the parser unchanged when it is followed by a blank, tab,
newline, equal sign, or left parenthesis. Any input line that
contains history substitution is echoed on the terminal before it is
executed for verification.
Commands input from the terminal that 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 number of previous commands saved is controlled by the history
variable. The previous command is always saved, regardless of its
value. Commands are numbered sequentially from 1.
You can refer to previous events by event number (such as !10 for
event 10), relative event location (such as !-2 for the second
previous event), full or partial command name (such as !d for the last
event using a command with initial character d), and string expression
(such as !?mic? referring to an event containing the characters mic).
These forms, without further modification, simply reintroduce the
words of the specified events, each separated by a single blank. As a
special case, !! is a re-do; it refers to the previous command.
To select words from a command, use a colon (:) and a designator for
the desired words after the event specification. The words of an
input line are numbered from zero. The basic word designators are:
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0 First word (i.e., the command name itself).
n nth word.
^ First argument. (This is equivalent to 1.)
$ Last word.
a-b Range of words from a through b. Special cases are -y, an
abbreviation for ``word 0 through word y''; and x-, which
means ``word x up to, but not including, word $''.
* Range from the second word through the last word.
% Used with a search sequence to substitute the immediately
preceding matching word.
The colon separating the command specification from the word
designator can be omitted if the argument selector begins with a ^, $,
*, -, or %.
After word designator can be followed by a sequence of modifiers, each
preceded by a colon. The following modifiers are defined:
h Use only the first component of a path name by removing all
following components.
r Use the root file name by removing any trailing suffix
(.xxx).
e Use the file name's trailing suffix (.xxx) by removing the
root name.
s /l/r
substitute the value of r for the value l in the indicated
command.
t Use only the final file name of a path name by removing all
leading path name components.
& Repeat the previous substitution.
p Print the new command but do not execute it.
q Quote the substituted words, preventing further
substitutions.
x Like q, but break into words at blanks, tabs and newlines.
g Use a global command as a prefix to another modifier to
cause the specified change to be made globally. All words
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in the command are changed, one change per word, and each
string enclosed in single quotes (') or double quotes (") is
treated as a single word.
Unless preceded by a g, the modification is applied only to the first
modifiable word. An error results if a substitution is attempted and
cannot be completed (i.e., if you ask for a substitution of !11 on a
history buffer containing only 10 commands).
The left hand side of substitutions are strings; not regular
expressions in the sense of HP-UX editors. Any character can be used
as the delimiter in place of a slash (/). Use a backslash to quote a
delimiter character if it is used in the l or r string. The character
& in the right-hand side is replaced by the text from the left. A \
also quotes &. A null l string uses the previous string either from
an l or from a contextual scan string s in !?s?. The trailing
delimiter in the substitution can be omitted if a new-line character
follows immediately, as may the trailing ? in a contextual scan.
A history reference can be given without an event specification (as in
!$). In this case, the reference is to the previous command unless a
previous history reference occurred on the same line, in which case
this form repeats the previous reference. Thus
!?foo?^ !$
gives the first and last arguments from the command matching ?foo?.
A special abbreviation of a history reference occurs when the first
non-blank character of an input line is a circumflex (^). This is
equivalent to !:s^, providing a convenient shorthand for substitutions
on the text of the previous line. Thus ^lb^lib fixes the spelling of
lib in the previous command.
Finally, a history substitution can be enclosed within curly braces
{ } if necessary to insulate it from the characters which follow.
Thus, after
ls -ld ~paul
one could execute !{l}a to do
ls -ld ~paula
while !la would look for a command starting with la.
Quoting with Single and Double Quotes
The quotation of strings by single quotes (') and double quotes (")
can be used to prevent all or some of the remaining substitutions.
Strings enclosed in single quotes are protected from any further
interpretation. Strings enclosed in double quotes are still variable-
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and command-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 double-quoted string yield parts of more than one word; single-
quoted strings never do.
Alias Substitution
csh maintains a list of aliases that can be established, displayed,
and modified by the alias and unalias commands. After a command line
is scanned, it is parsed into distinct commands and the first word of
each command, left-to-right, is checked to see if it has an alias. If
it does, the text which is the alias for that command is reread with
the history mechanism available as if that command was the previous
input line. The resulting words replace the command and argument
list. If no reference is made to the history list, the argument list
is left unchanged.
Thus, if the alias for ls is ls -l, the command ls /usr maps to ls -l
/usr, leaving the argument list undisturbed. Similarly, if the alias
for lookup was grep !^ /etc/passwd, lookup bill maps to grep bill
/etc/passwd .
If an alias is found, the word transformation of the input text is
performed and the aliasing process begins again on the re-formed input
line. Looping is prevented if the first word of the new text is the
same as the old by flagging it to prevent further aliasing. Other
loops are detected and cause an error.
Note that the mechanism allows aliases to introduce parser metasyntax.
Thus:
alias print 'pr \!* | lp'
makes a command that uses pr(1) to print its arguments on the line
printer.
Expressions
Some of the built-in commands 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 (shown in order of increasing
precedence):
|| && | ^ & == != =~ !~ <= >= < > << >> + - * / % ! ~ ( )
The following list shows the grouping of these operators. The
precedence decreases from top to bottom in the list:
* / %
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+ -
<< >>
<= >= < >
== != =~ !~
The operators ==, !=, =~, and !~ compare their arguments as strings;
all others operate on numbers. The operators =~ and !~ are similar to
!= and ==, except that the right-hand side is a pattern (containing
*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 beginning with 0 are considered octal numbers. Null or
missing arguments are considered 0. The result of all expressions are
strings that represent decimal numbers. It is important to note that
no two components of an expression can appear in the same word. These
components should be surrounded by spaces except when adjacent to
components of expressions that are syntactically significant to the
parser: -, &, |, <, >, (, and ).
Also available in expressions as primitive operands are command
executions enclosed in curly braces ({ }) and file enquiries of the
form -l filename, 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 filename is command- and file-name expanded then tested
to see if it has the specified relationship to the real user. If the
file does not exist or is inaccessible, all inquiries return false
(0). Command executions succeed, returning true, if the command exits
with status 0; otherwise they fail, returning false. If more detailed
status information is required, the command should be executed outside
of an expression and the status variable examined.
Control of the Flow
csh contains a number of commands that can be used to regulate the
flow of control in command files (shell scripts) and (in limited but
useful ways) from terminal input. These commands all operate by
forcing the shell to reread or skip parts of its input and, due to the
implementation, restrict the placement of some of the commands.
The foreach, switch, and while statements, as well as the if-then-else
form of the if statement require that the major keywords appear in a
single simple command on an input line as shown below.
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If the shell's input is not seekable, the shell buffers 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 gotos succeed on non-seekable inputs.)
Signal Handling
csh normally ignores quit signals. Jobs running in background mode
are immune to signals generated from the keyboard, including hangups.
Other signals have the values which the shell inherited from its
parent. csh's 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 Line Parsing
csh splits input lines into words at blanks and tabs. The following
exceptions (parser metacharacters) are considered separate words:
& ampersand;
| vertical bar;
; semicolon;
< less-than sign;
> greater-than sign;
( left parenthesis;
) right parenthesis;
&& double ampersand;
|| double vertical bar;
<< double less-than sign;
>> double greater-than sign;
# comment delimiter
The backslash (\) removes the special meaning of these parser
metacharacters. A parser metacharacter preceded by a backslash is
interpreted as its ASCII value. A newline character (ASCII 10)
preceded by a backslash is equivalent to a blank.
Strings enclosed in single or double quotes form parts of a word.
Metacharacters in these strings, including blanks and tabs, do not
form separate words. Within pairs of backslashes or quotes, a newline
preceded by a backslash gives a true newline character.
When csh's input is not a terminal, the # charactercharacter
introduces a comment terminated by a newline.
CSH VARIABLES
csh maintains a set of variables. Each variable has a value equal to
zero or more strings (words). Variables have names consisting of up
to 20 letters and digits starting with a letter. The underscore
character is considered a letter. The value of a variable may be
displayed and changed by using the set and unset commands. Some of
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the variables are Boolean, that is, the shell does not care what their
value is, only whether they are set or not.
Some operations treat variables numerically. The at sign (@) command
permits numeric calculations to be performed and the result assigned
to a variable. The null string is considered to be zero, and any
subsequent words of multi-word values are ignored.
After the input line is aliased and parsed, and before each command is
executed, variable expansion is performed keyed by the dollar sign
($)character. Variable expansion can be prevented by preceding the
dollar sign with a backslash character (\) except within double quotes
(") where substitution always occurs. Variables are never expanded if
enclosed in single quotes. Strings quoted by single quotes are
interpreted later (see Command Substitution) so variable substitution
does not occur there until later, if at all. A dollar sign 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.
Unless enclosed in double quotes or given the :q modifier, the results
of variable substitution may eventually be command and file name
substituted. Within double quotes, a variable whose value consists of
multiple words expands to a portion of a single word, with the words
of the variable's value separated by blanks. When the :q modifier is
applied to a substitution, the variable expands to multiple words with
each word separated by a blank and quoted to prevent later command or
file name substitution.
The following metasequences are provided for introducing variable
values into the shell input. Except as noted, it is an error to
reference a variable that is not set.
$variable_name
${variable_name}
When interpreted, this sequence is replaced by the words of
the value of the variable variable_name, each separated by a
blank. Braces insulate variable_name from subsequent
characters that would otherwise be interpreted to be part of
the variable name itself.
If variable_name is not a csh variable, but is set in the
environment, that value is used. Non-csh variables cannot
be modified as shown below.
$variable_name[selector]
${variable_name[selector]}
This modification selects only some of the words from the
value of variable_name. The selector is subjected to
variable substitution, and can consist of a single number or
two numbers separated by a dash. The first word of a
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variable's value is numbered 1. If the first number of a
range is omitted it defaults to 1. If the last member of a
range is omitted it defaults to the total number of words in
the variable ($#variable_name). An asterisk metacharacter
used as a selector selects all words.
$#variable_name
${#variable_name}
This form gives the number of words in the variable, and is
useful for forms using a [selector] option.
$0 This form substitutes the name of the file from which
command input is being read. An error occurs if the file
name is not known.
$number
${number}
This form is equivalent to an indexed selection from the
variable argv ($argv[number]).
$* This is equivalent to selecting all of argv ($argv[*]).
The modifiers :h, :t, :r, :q, and :x can be applied to the
substitutions above, as can CR :gh , CR :gt , and CR :gr . If curly
braces ({ }) appear in the command form, the modifiers must appear
within the braces. The current implementation allows only one :
modifier on each $d expansion.
The following substitutions cannot be modified with : modifiers:
$?variable_name
${?variable_name}
Substitutes the string 1 if variable_name is set, 0 if it is
not.
$?0 Substitutes 1 if the current input file name is known, 0 if
it is not.
$$ Substitutes the (decimal) process number of the (parent)
shell.
$< Substitutes a line from the standard input, with no further
interpretation thereafter. It can be used to read from the
keyboard in a shell script.
Pre-Defined and Environment Variables
The following variables have special meaning to the shell. Of these
autologout, argv, cwd, home, path, prompt, shell, and status are
always set by the shell. Except for cwd and status, this setting
occurs only at initialization (initial execution of csh). These
variables are not modified unless modified explicitly by the user.
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csh copies the HP-UX environment variable USER into the shell variable
user, the environment variable TERM into term, the environment
variable HOME into home, and PATH into path. csh copies these values
back into the environment whenever the csh variables are reset.
In a windowed environment, if csh detects that the window has changed
size, csh sets the environment variables LINES and COLUMNS to match
the new window size.
argv This variable is set to the arguments of the csh
command statement. It is from this variable that
positional parameters are substituted; i.e., $1 is
replaced by $argv[1], etc.
cdpath This variable gives a list of alternate
directories searched to find subdirectories in
chdir commands.
cwd This variable contains the absolute path name of
the current working directory. Whenever changing
directories (using cd), this variable is updated.
echo This variable is set by the -x command line
option. If set, all built-in commands and their
arguments are echoed to the standard output device
just before being executed. Built-in commands are
echoed before command and file name substitution,
since these substitutions are then done
selectively. For non-built-in commands, all
expansions occur before echoing.
hidden If set, csh includes unmatched CDFs in expansions
(see cdf(4)). Also, unmatched CDFs are displayed
with a trailing + when using the control-D command
to display matching file names (see the CSH
UTILITIES section). By default, hidden is not
set.
history This variable is used to create the command
history buffer and to set its size. If this
variable is not set, no command history is
maintained and history substitutions cannot be
made. Very large values of history can cause
shell memory overflow. Values of 10 or 20 are
normal. All commands, executable or not, are
saved in the command history buffer.
home This variable contains the absolute path name to
your home directory. The variable home is
initialized from the HP-UX environment. File name
expansion of tilde (~) refers to this variable.
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ignoreeof If set, csh ignores end-of-file characters from
input devices that are terminals. csh exits
normally when it encounters the end-of-file
condition (CTRL-D typed as the first character on
a command line). Setting ignoreeof prevents the
current shell from being killed by an accidental
(CTRL-D. However, to prevent an infinite loop of
EOF input, csh terminates if it receives 26
consecutive EOFs.
mail This variable contains a list of the files where
csh checks for your mail. csh periodically
(default is 10 minutes) checks this variable
before producing a prompt upon command completion.
If the variable contains a file name that has been
modified since the last check (resulting from mail
being put in the file), csh prints You have new
mail.
If the first word of the value of mail is numeric,
that number specifies a different mail checking
interval in seconds.
If multiple mail files are specified, the shell
says New mail in file_name, where file_name is the
file containing the mail.
noclobber This variable places restrictions on output
redirection to ensure that files are not
accidentally destroyed, and that commands using
append redirection (>>) refer to existing files.
noglob If set, file name expansion is inhibited. This is
most useful in shell scripts that 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 no longer an error for a file name
expansion to not match any existing files. If
there is no match, the primitive pattern is
returned. It is still an error for the primitive
pattern to be malformed. For example, 'echo ['
still gives an error.
notify If set, csh notifies you immediately (through your
standard output device) of background job
completions. The default is unset (indicate job
completions just before printing a prompt).
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path Each word of the path variable specifies a
directory in which commands are to be sought for
execution. A null word specifies your current
working directory. If there is no path variable,
only full path names can be executed. When path
is not set and when users do not specify full path
names, csh searches for the command through the
directories . (current directory), /bin, and
/usr/bin. A csh which is given neither the -c nor
the -t option normally hashes the contents of the
directories in the path variable after reading
.cshrc, and each time the path variable is reset.
If new commands are added to these directories
while the shell is active, it is necessary to
execute rehash for csh to access these new
commands.
prompt This variable lets you select your own prompt
character string. The prompt is printed before
each command is read from an interactive terminal
input. If a ! appears in the string, it is
replaced by the current command history buffer
event number unless a preceding \ is given. The
default prompt is the percent sign (%) for users
and the # character for the super-user.
shell This variable contains the name of the file in
which the csh program resides. This variable is
used in forking shells to interpret files that
have their execute bits set but which are not
executable by the system. (See the description of
Non-Built-In Command Execution).
status This variable contains the status value returned
by the last command. If the command terminated
abnormally, 0200 is added to the status variable's
value. Built-in commands which terminated
abnormally return exit status 1, and all other
built-in commands set status to 0.
time This variable contains a numeric value that
controls the automatic timing of commands. If
set, csh prints, for any command taking more than
the specified number of cpu seconds, a line of
information to the standard output device giving
user, system, and real execution times plus a
utilization percentage. The utilization
percentage is the ratio of user plus system times
to real time. This message is printed after the
command finishes execution.
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verbose This variable is set by the -v command line
option. If set, the words of each command are
printed on the standard output device after
history substitutions have been made.
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 that 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 grave
accents (` ...`). 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
double quotes, only newlines force new words; blanks and tabs are
preserved.
In any case, the single final newline does not force a new word. Note
that it is thus possible for a command substitution to yield only part
of a word, even if the command outputs a complete line.
File name Substitution
Each command word is processed as a pattern for file name
substitution, also known as globbing, and replaced with a sorted list
of file names which match the pattern. The form of the patterns is
the Pattern Matching Notation defined by regexp(5) with the following
exceptions:
o Non-matching lists in bracket expressions are not supported.
o 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.
o 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
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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 can 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 substitution, and
each input line is compared to word before any
substitutions are done on this input line. Unless
a quoting \, ", ", ', or ` appears in word,
variable and command substitution is performed on
the intervening lines, allowing \ to quote $, \
and `. Commands which are substituted have all
blanks, tabs, and newlines preserved, except for
the final newline which is dropped. The resultant
text is placed in an anonymous temporary file
which is given to the command as standard input.
> name
>! name
>& name
>&! name The file name is used as standard output. If the
file does not exist, it is created; if the file
exists, it is truncated, and its previous contents
are lost.
If the variable noclobber is set, 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 exclamation point (!) forms can be
used to suppress this check.
The forms involving the ampersand character (&)
route the standard error into the specified file
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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 the same as >,
but appends output to the end of the file. If the
variable noclobber is set, it is an error for the
file not to exist unless one of the ! forms is
given. Otherwise, it is 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
executed from a shell script 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 scripts to function as components of pipelines and
allows the shell to block-read its input.
Diagnostic output can be directed through a pipe with the standard
output. Simply use the form |& rather than | by itself.
CSH UTILITIES
File Name Completion
In typing file names as arguments to commands, it is no longer
necessary to type a complete name, only a unique abbreviation is
necessary. When you want the system to try to match your
abbreviation, press the ESC key. The system then completes the file
name for you, echoing the full name on your terminal. If the
abbreviation does not match an available file name, the terminal's
bell is sounded. The file name may be partially completed if the
prefix matches several longer file names. In this case, the name is
extended up to the ambiguous deviation, and the bell is sounded.
File name completion works equally well when other directories are
addressed. In addition, the tilde (~) convention for home directories
is understood in this context.
Viewing a File or Directory List
At any point in typing a command, you can request "what files are
available" or "what files match my current specification". Thus, when
you have typed:
% cd ~speech/data/bench/fritz/
you may wish to know what files or subdirectories exist (in
~speech/data/bench/fritz), without aborting the command you are
typing. Typing CTRL-D at this point lists the files available. Files
are listed in multicolumn format, sorted by column. Directories and
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executable files are identified by a trailing / and *, respectively.
Once printed, the command is re-echoed for you to complete.
Additionally, you may want to know which files match a prefix, the
current file specification so far. If you had typed:
% cd ~speech/data/bench/fr
followed by a CTRL-D, all files and subdirectories whose prefix was fr
in the directory ~speech/data/bench would be printed. Notice that the
example before was simply a degenerate case of this with a null
trailing file name. (The null string is a prefix of all strings.)
Notice also that a trailing slash is required to pass to a new sub-
directory for both file name completion and listing. Note that the
degenerate case
% ~^D
prints a full list of login names on the current system.
Command Name Recognition
Command name recognition and completion works in the same manner as
file name recognition and completion above. The current value of the
environment variable PATH is used in searching for the command. For
example
% newa [Escape]
might expand to
% newaliases
Also,
% new [Control]-[D]
lists all commands (along PATH) that begin with new. As an option, if
the shell variable listpathnum is set, a number indicating the index
in PATH is printed next to each command on a [Control]-[D] listing.
Autologout
A new shell variable has been added called autologout. If the
terminal remains idle (no character input) at the shell's top level
for a number of minutes greater than the value assigned to autologout,
you are automatically logged off. The autologout feature is
temporarily disabled while a command is executing. The initial value
of autologout is 60. If unset or set to 0, autologout is entirely
disabled.
Command Line Control
A ^R re-prints the current command line; ^W erases the last word
entered on the current command line.
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Sanity
C shell restores your terminal to a sane mode if it appears to return
from some command in raw, cbreak, or noecho mode.
Saving Your History Buffer
csh has the ability to save your history list between login sessions.
If the shell variable savehist is set to a number, that number of
command events from your history list is saved. For example, placing
the line
set history=10 savehist=10
in your .cshrc file maintains a history buffer of length 10 and saves
the entire list when you logout. When you log back in, the entire
buffer is restored. The commands are saved in the file .history in
your login directory.
EXTERNAL INFLUENCES
Environment Variables
LC_COLLATE determines the collating sequence used in evaluating
pattern matching notation for file name substitution.
LC_CTYPE determines the interpretation of text as single and/or
multi-byte characters, the classification of characters as letters,
and the characters matched by character class expressions in pattern
matching notation.
LANG determines the language in which messages are displayed.
If LC_COLLATE or LC_CTYPE is not specified in the environment or is
set to the empty string, the value of LANG is used as a default for
each unspecified or empty variable. If LANG is not specified or is
set to the empty string, a default of "C" (see lang(5)) is used
instead of LANG. If any internationalization variable contains an
invalid setting, csh behaves as if all internationalization variables
are set to "C". See environ(5).
International Code Set Support
Single- and multi-byte character code sets are supported.
WARNINGS
The .cshrc file should be structured such that it cannot generate any
output on standard output or standard error, including occasions when
it is invoked without an affiliated terminal. rcp(1) causes .cshrc to
be sourced, and any output generated by this file, even to standard
error causes problems. Commands such as stty(1) should be placed in
.login, not in .cshrc, so that their output cannot affect rcp(1).
csh has certain 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 file name
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expansion is limited to one-sixth 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
substitutions on a single line to 20.
When a command is restarted from a stop, csh prints the directory it
started in if it is different from the current directory; this can be
misleading (i.e., wrong) because 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 interrupt b, the shell then immediately
executes c. This is especially noticeable if this expansion results
from an alias. It suffices to place the sequence of commands in
parentheses to force it into a subshell; i.e., ( a ; b ; c ).
Because of the signal handling required by csh, interrupts are
disabled just before a command is executed, and restored as the
command begins execution. There may be a few seconds delay between
when a command is given and when interrupts are recognized.
Control over tty output after processes are started is primitive;
perhaps this will inspire someone to work on a good virtual terminal
interface. In a virtual terminal interface much more interesting
things could be done with output control.
Alias substitution is most often used to clumsily simulate shell
procedures; shell procedures should be provided rather than aliases.
Commands within loops, prompted for by ?, are not placed in the
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.
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.
Terminal type is examined only the first time you attempt recognition.
To list all commands on the system along PATH, enter [Space]-[Ctrl]-
[D].
The csh metasequence !~ does not work.
In an international environment, character ordering is determined by
the setting of LC_COLLATE, rather than by the binary ordering of
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character values in the machine collating sequence. This brings with
it certain attendant dangers, particulary when using range expressions
in file name generation patterns. For example, the command,
rm [a-z]*
might be expected to match all file names beginning with a lowercase
alphabetic character. However, if dictionary ordering is specified by
LC_COLLATE, it would also match file names beginning with an uppercase
character (as well as those beginning with accented letters).
Conversely, it would fail to match letters collated after z in
languages such as Norwegian.
The correct (and safe) way to match specific character classes in an
international environment is to use a pattern of the form:
rm [[:lower:]]*
This uses LC_CTYPE to determine character classes and works
predictably for all supported languages and codesets. For shell
scripts produced on non-internationalized systems (or without
consideration for the above dangers), it is recommended that they be
executed in a non-NLS environment. This requires that LANG,
LC_COLLATE, etc., be set to "C" or not set at all.
csh implements command substitution by creating a pipe between itself
and the command. If the root file system is full, the substituted
command cannot write to the pipe. As a result, the shell receives no
input from the command, and the result of the substitution is null.
In particular, using command substitution for variable assignment
under such circumstances results in the variable being silently
assigned a NULL value.
Relative path changes (such as cd ..), when in a symbolically linked
directory, cause csh's knowledge of the working directory to be along
the symbolic path instead of the physical path.
Prior to HP-UX Release 9.0, csh, when getting its input from a file,
would exit immediately if unable to execute a command (such as if it
was unable to find the command). Beginning at Release 9.0, csh
continues on and attempts to execute the remaining commands in the
file. However, if the old behavior is desired for compatibility
purposes, set the environment variable EXITONERR to 1.
AUTHOR
csh was developed by the University of California, Berkeley and HP.
FILES
~/.cshrc A csh script sourced (executed) at the
beginning of execution by each shell. See
WARNINGS
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csh(1) csh(1)
~/.login A csh script sourced (executed) by login
shell, after .cshrc at login.
~/.logout A csh script sourced (executed) by login
shell, at logout.
/etc/passwd Source of home directories for ~name.
/bin/sh Standard shell, for shell scripts not
starting with a #.
/etc/csh.login A csh script sourced (executed) before
~/.cshrc and ~/.login when starting a csh
login (analogous to /etc/profile in the
Bourne shell).
/tmp/sh* Temporary file for <<.
SEE ALSO
sh(1), access(2), exec(2), fork(2), pipe(2), umask(2), wait(2),
tty(7), a.out(4), environ(5), lang(5), regexp(5).
C Shell tutorial in Shells Users Guide .
Hewlett-Packard Company - 31 - HP-UX Release 9.0: August 1992