modern syntax for asgops & inits cause Donn's latest ccom rejects the old.

[unix-history] / usr / src / bin / csh / USD.doc / csh.g

.\" Copyright (c) 1980 Regents of the University of California.
.\" All rights reserved.  The Berkeley software License Agreement
.\" specifies the terms and conditions for redistribution.
.\"
.\"	@(#)csh.g	6.1 (Berkeley) %G%
.\"

.SH
Glossary
.PP
This glossary lists the most important terms introduced in the
introduction to the
shell and gives references to sections of the shell
document for further information about them.
References of the form
`pr (1)'
indicate that the command
.I pr
is in the \s-2UNIX\s0 User Reference manual in section 1.
You can look at an online copy of its manual page by doing
.DS
man 1 pr
.DE
References of the form (2.5)
indicate that more information can be found in section 2.5 of this
manual.
.IP \&\fB.\fR 15n
Your current directory has the name `.' as well as the name printed
by the command
.I pwd;
see also
.I dirs.
The current directory `.' is usually the first 
.I component 
of the search path contained in the variable
.I path ,
thus commands which are in `.' are found first (2.2).
The character `.' is also used in separating 
.I components 
of filenames
(1.6).
The character `.' at the beginning of a 
.I component 
of a 
.I pathname 
is treated specially and not matched by the 
.I "filename expansion"
metacharacters `?', `*', and `[' `]' pairs (1.6).
.IP \&\fB..\fR
Each directory has a file `..' in it which is a reference to its
parent directory.
After changing into the directory with
.I chdir ,
i.e.
.DS
chdir paper
.DE
you can return to the parent directory by doing
.DS
chdir ..
.DE
The current directory is printed by
.I pwd
(2.7).
.IP a.out
Compilers which create executable images create them, by default, in the
file 
.I a.out.
for historical reasons (2.3).
.IP "absolute pathname"
.br
A 
.I pathname 
which begins with a `/' is
.I absolute
since it specifies the 
.I path 
of directories from the beginning
of the entire directory system \- called the
.I root
directory.  
.I Pathname s 
which are not
.I absolute
are called
.I relative
(see definition of
.I "relative pathname" )
(1.6).
.IP alias
An
.I alias
specifies a shorter or different name for a \s-2UNIX\s0
command, or a transformation on a command to be performed in
the shell.
The shell has a command
.I alias
which establishes 
.I aliases 
and can print their current values.
The command
.I unalias
is used to remove 
.I aliases 
(2.4).
.IP argument
Commands in \s-2UNIX\s0 receive a list of 
.I argument 
words.
Thus the command
.DS
echo a b c
.DE
consists of the
.I "command name"
`echo' and three 
.I argument 
words `a', `b' and `c'.
The set of 
.I arguments 
after the
.I "command name"
is said to be the
.I "argument list"
of the command (1.1).
.IP argv
The list of arguments to a command written in the shell language
(a shell script or shell procedure) is stored in a variable called
.I argv
within the shell.
This name is taken from the conventional name in the
C programming language (3.4).
.IP background
Commands started without waiting for them to complete are called
.I background
commands (2.6).
.IP base
A filename is sometimes thought of as consisting of a
.I base
part, before any `.' character, and an 
.I extension 
\- the part after
the `.'.  See
.I filename
and
.I extension
(1.6) and basename (1).
.IP bg
The
.I bg
command causes a
.I suspended 
job to continue execution in the
.I background
(2.6).
.IP bin
A directory containing binaries of programs and shell scripts to be
executed is typically called a 
.I bin 
directory.
The standard system 
.I bin 
directories are `/bin' containing the most
heavily used commands and `/usr/bin' which contains most other user
programs.
Programs developed at UC Berkeley live in `/usr/ucb', while locally
written programs live in `/usr/local'.  Games are kept in the directory
`/usr/games'.
You can place binaries in any directory.
If you wish to execute them often, the name of the directories
should be a 
.I component 
of the variable
.I path .
.IP break
.I Break
is a builtin command used to exit from loops within the control
structure of the shell (3.7).
.IP breaksw
The
.I breaksw
builtin command is used to exit from a
.I switch
control structure, like a
.I break
exits from loops (3.7).
.IP builtin
A command executed directly by the shell is called a
.I builtin
command.
Most commands in \s-2UNIX\s0 are not built into the shell,
but rather exist as files in 
.I bin 
directories.
These commands are accessible because the directories in which
they reside are named in the
.I path
variable.
.IP case
A
.I case
command is used as a label in a
.I switch
statement in the shell's control structure, similar to that of the
language C.
Details are given in the shell documentation `csh (1)' (3.7).
.IP cat
The
.I cat
program catenates a list of specified files on the 
.I "standard output" .
It is usually used to look at the contents of a single file on the terminal,
to `cat a file' (1.8, 2.3).
.IP cd
The
.I cd
command is used to change the 
.I "working directory" .
With no arguments,
.I cd
changes your 
.I "working directory" 
to be your
.I home
directory (2.4, 2.7).
.IP chdir
The
.I chdir
command is a synonym for
.I cd .
.I Cd
is usually used because it is easier to type.
.IP chsh
The
.I chsh
command is used to change the shell which you use on \s-2UNIX\s0.
By default, you use an different version of the shell
which resides in `/bin/sh'.
You can change your shell to `/bin/csh' by doing
.DS
chsh your-login-name /bin/csh
.DE
Thus I would do
.DS
chsh bill /bin/csh
.DE
It is only necessary to do this once.
The next time you log in to \s-2UNIX\s0 after doing this command,
you will be using
.I csh
rather than the shell in `/bin/sh' (1.9).
.IP cmp
.I Cmp
is a program which compares files.
It is usually used on binary files, or to see if two files are identical (3.6).
For comparing text files the program
.I diff ,
described in `diff (1)' is used.
.IP command
A function performed by the system, either by the shell
(a builtin 
.I command )
or by a program residing in a file in
a directory within the \s-2UNIX\s0 system, is called a
.I command
(1.1).
.IP "command name"
.br
When a command is issued, it consists of a
.I "command name" ,
which is the first word of the command,
followed by arguments.
The convention on \s-2UNIX\s0 is that the first word of a
command names the function to be performed (1.1).
.IP "command substitution"
.br
The replacement of a command enclosed in `\`' characters
by the text output by that command 
is called
.I "command substitution"
(4.3).
.IP component
A part of a
.I pathname
between `/' characters is called a
.I component
of that 
.I pathname .
A variable
which has multiple strings as value is said to have
several
.I component s;
each string is a
.I component
of the variable.
.IP continue
A builtin command which causes execution of the enclosing
.I foreach
or
.I while
loop to cycle prematurely.
Similar to the
.I continue
command in the programming language C (3.6).
.IP control-
Certain special characters, called
.I control
characters, are produced by holding down the \s-2CONTROL\s0 key
on your terminal and simultaneously pressing another character, much like
the \s-2SHIFT\s0 key is used to produce upper case characters. Thus
.I control- c
is produced by holding down the \s-2CONTROL\s0 key while pressing the
`c' key.  Usually \s-2UNIX\s0 prints an caret (^) followed by the
corresponding letter when you type a
.I control
character (e.g. `^C' for
.I control- c
(1.8).
.IP "core\ dump"
When a program terminates abnormally, the system places an image
of its current state in a file named `core'.
This 
.I "core dump"
can be examined with the system debugger `adb (1)'
or `sdb (1)' in order to determine what went wrong with the program (1.8).
If the shell produces a message of the form
.DS
Illegal instruction (core dumped)
.DE
(where `Illegal instruction' is only one of several possible
messages), you should report this to the author of the program
or a system administrator, 
saving the `core' file.
.IP cp
The
.I cp
(copy) program is used to copy the contents of one file into another
file.
It is one of the most commonly used \s-2UNIX\s0 commands (1.6).
.IP csh
The name of the shell
program that this document describes.
.IP \&.cshrc
The file
.I \&.cshrc
in your
.I home
directory is read by each shell as it begins execution.
It is usually used to change the setting of the variable
.I path
and to set
.I alias
parameters which are to take effect globally (2.1).
.IP cwd
The
.I cwd
variable in the shell holds the
.I "absolute pathname"
of the current
.I "working directory" \&.
It is changed by the shell whenever your current
.I "working directory"
changes and should not be changed otherwise (2.2).
.IP date
The
.I date
command prints the current date and time (1.3).
.IP debugging
.I Debugging
is the process of correcting mistakes in programs and shell scripts.
The shell has several options and variables which may be used
to aid in shell 
.I debugging 
(4.4).
.IP default:
The label
.I default:
is used within shell
.I switch
statements, as it is in the C language
to label the code to be executed if none of the
.I case
labels matches the value switched on (3.7).
.IP \s-2DELETE\s0
The
\s-2DELETE\s0
or
\s-2RUBOUT\s0
key on the terminal normally causes an interrupt to be sent to the current job.
Many users change the interrupt character to be ^C.
.IP detached
A command that continues running in the 
.I background 
after you logout is said to be 
.I detached .
.IP diagnostic
An error message produced by a program is often referred to as a
.I diagnostic .
Most error messages are not written to the 
.I "standard output" ,
since that is often directed away from the terminal (1.3, 1.5).
Error messsages are instead written to the
.I "diagnostic output"
which may be directed away from the terminal, but usually is not.
Thus 
.I diagnostics 
will usually appear on the terminal (2.5).
.IP directory
A structure which contains files.
At any time you are in one particular 
.I directory 
whose names can be printed by the command 
.I pwd .
The
.I chdir
command will change you to another 
.I directory , 
and make the files
in that 
.I directory 
visible. The 
.I directory 
in which you are when you first login is your
.I home
directory (1.1, 2.7).
.IP "directory\ stack"
The shell saves the names of previous
.I "working directories"
in the
.I "directory stack"
when you change your current
.I "working directory"
via the
.I pushd
command.  The
.I "directory stack"
can be printed by using the
.I dirs
command, which includes your current
.I "working directory"
as the first directory name on the left (2.7).
.IP dirs
The
.I dirs
command prints the shell's
.I "directory stack" 
(2.7).
.IP du
The
.I du
command is a program (described in `du (1)') which
prints the number of disk blocks is all directories below
and including your current
.I "working directory"
(2.6).
.IP echo
The
.I echo
command prints its arguments (1.6, 3.6).
.IP else
The
.I else
command is part of the `if-then-else-endif' control
command construct (3.6).
.IP endif
If an
.I if
statement is ended with the word
.I then ,
all lines following the
.I if
up to a line starting with the word
.I endif
or
.I else
are executed if the condition between parentheses after the
.I if
is true (3.6).
.IP \s-2EOF\s0
An
.I "end\f1-\fPof\f1-\fPfile"
is generated by the terminal by a control-d,
and whenever a command reads to the end of a file which
it has been given as input.
Commands receiving input from a
.I pipe
receive an 
.I "end\f1-\fPof\f1-\fPfile" 
when the command sending them input completes.
Most commands terminate when they receive an 
.I "end\f1-\fPof\f1-\fPfile" .
The shell has an option to ignore 
.I "end\f1-\fPof\f1-\fPfile" 
from a terminal
input which may help you keep from logging out accidentally
by typing too many control-d's (1.1, 1.8, 3.8).
.IP escape
A character `\e' used to prevent the special meaning of a metacharacter
is said to
.I escape
the character from its special meaning.
Thus
.DS
echo \e*
.DE
will echo the character `*' while just
.DS
echo *
.DE
will echo the names of the file in the current directory.
In this example, \e
.I escape s
`*' (1.7).
There is also a non-printing character called
.I escape , 
usually labelled
\s-2ESC\s0
or
\s-2ALTMODE\s0
on terminal keyboards.
Some older \s-2UNIX\s0 systems use this character to indicate that
output is to be 
.I suspended . 
Most systems use control-s to stop the output and control-q to start it.
.IP /etc/passwd
This file contains information about the accounts currently on the
system.
It consists of a line for each account with fields separated by
`:' characters (1.8).
You can look at this file by saying
.DS
cat /etc/passwd
.DE
The commands
.I finger
and
.I grep
are often used to search for information in this file.
See `finger (1)', `passwd(5)', and `grep (1)' for more details.
.IP exit
The
.I exit
command is used to force termination of a shell script,
and is built into the shell (3.9).
.IP "exit\ status"
A command which discovers a problem may reflect this back to the command
(such as a shell) which invoked (executed) it.
It does this by returning a non-zero number as its
.I "exit status" ,
a status of zero being considered
`normal termination'.
The
.I exit
command can be used to force a shell command script to give a non-zero
.I "exit status" 
(3.6).
.IP expansion
The replacement of strings in the shell input which contain metacharacters
by other strings is referred to as the process of
.I expansion .
Thus the replacement of the word `*' by a sorted list of files
in the current directory is a `filename expansion'.
Similarly the replacement of the characters `!!' by the text of
the last command is a `history expansion'.
.I Expansions 
are also referred to as
.I substitutions
(1.6, 3.4, 4.2).
.IP expressions
.I Expressions 
are used in the shell
to control the conditional structures used in the writing of shell
scripts and in calculating values for these scripts.
The operators available in shell 
.I expressions 
are those of the language
C (3.5).
.IP extension
Filenames often consist of a
.I base
name and an
.I extension
separated by the character `.'.
By convention, groups of related files often share the same 
.I root 
name.
Thus if `prog.c' were a C program, then the object file for this
program would be stored in `prog.o'.
Similarly a paper written with the
`\-me'
nroff macro package might be stored in
`paper.me'
while a formatted version of this paper might be kept in
`paper.out' and a list of spelling errors in
`paper.errs' (1.6).
.IP fg
The
.I "job control"
command
.I fg
is used to run a
.I background
or
.I suspended
job in the
.I foreground
(1.8, 2.6).
.IP filename
Each file in \s-2UNIX\s0 has a name consisting of up to 14 characters
and not including the character `/' which is used in
.I pathname
building.  Most 
.I filenames
do not begin with the character `.', and contain 
only letters and digits with perhaps a `.' separating the
.I base
portion of the 
.I filename 
from an 
.I extension 
(1.6).
.IP "filename expansion"
.br
.I "Filename expansion" 
uses the metacharacters `*', `?' and `[' and `]'
to provide a convenient mechanism for naming files.
Using 
.I "filename expansion" 
it is easy to name all the files in
the current directory, or all files which have a common 
.I root 
name. Other 
.I "filename expansion" 
mechanisms use the metacharacter `~' and allow
files in other users' directories to be named easily (1.6, 4.2).
.IP flag
Many \s-2UNIX\s0 commands accept arguments which are not the names
of files or other users but are used to modify the action of the commands.
These are referred to as
.I flag
options, and by convention consist of one or more letters preceded by
the character `\-' (1.2).
Thus the
.I ls
(list files) command has an option
`\-s' to list the sizes of files.
This is specified
.DS
ls \-s
.DE
.IP foreach
The
.I foreach
command is used in shell scripts and at the terminal to specify
repetition of a sequence of commands while the value of a certain
shell variable ranges through a specified list (3.6, 4.1).
.IP foreground
When commands are executing in the normal way such that the
shell is waiting for them to finish before prompting for another
command they are said to be
.I "foreground jobs"
or
.I "running in the foreground" \&.  
This is as opposed to
.I background .
.I Foreground
jobs can be stopped by signals
from the terminal caused by typing different
control characters at the keyboard (1.8, 2.6).
.IP goto
The shell has a command
.I goto
used in shell scripts to transfer control to a given label (3.7).
.IP grep
The
.I grep
command searches through a list of argument files for a specified string.
Thus
.DS
grep bill /etc/passwd
.DE
will print each line in the file
.I "/etc/passwd"
which contains the string `bill'.
Actually,
.I grep
scans for 
.I "regular expressions"
in the sense of the editors
`ed (1)' and `ex (1)'.
.I Grep
stands for
`globally find 
.I "regular expression" 
and print' (2.4).
.IP head
The
.I head
command prints the first few lines of one or more files.
If you have a bunch of files containing text which you are wondering
about it is sometimes useful to run
.I head
with these files as arguments.
This will usually show enough of what is in these files to let you decide
which you are interested in (1.5).
.br
.I Head
is also used to describe the part of a
.I pathname
before and including the last `/' character.  The
.I tail
of a
.I pathname
is the part after the last `/'.  The `:h' and `:t' modifiers allow the
.I head
or
.I tail
of a 
.I pathname 
stored in a shell variable to be used (3.6).
.IP history
The
.I history
mechanism of the shell allows previous commands to be repeated,
possibly after modification to correct typing mistakes or to change
the meaning of the command.
The shell has a
.I "history list"
where these commands are kept, and a
.I history
variable which controls how large this list is (2.3).
.IP "home\ directory"
.br
Each user has a 
.I "home directory" ,
which is given in your entry
in the password file,
.I /etc/passwd .
This is the directory which you are placed in when you first login.
The
.I cd
or
.I chdir
command with no arguments takes you back to this directory, whose
name is recorded in the shell variable
.I home .
You can also access the 
.I "home directories" 
of other users in forming
filenames using a 
.I "filename expansion" 
notation and the character `~' (1.6).
.IP if
A conditional command within the shell, the
.I if
command is used in shell command scripts to make decisions
about what course of action to take next (3.6).
.IP ignoreeof
Normally, your shell will exit, printing
`logout'
if you type a control-d at a prompt of `% '.
This is the way you usually log off the system.
You can
.I set
the
.I ignoreeof
variable if you wish in your
.I \&.login
file and then use the command
.I logout
to logout.
This is useful if you sometimes accidentally type too many control-d
characters, logging yourself off
(2.2).
.IP input
Many commands on \s-2UNIX\s0 take information from the terminal or from
files which they then act on.
This information is called
.I input .
Commands normally read for 
.I input 
from their
.I "standard input"
which is, by default, the terminal.
This 
.I "standard input" 
can be redirected from a file using a shell metanotation
with the character `<'.
Many commands will also read from a file specified as argument.
Commands placed in 
.I pipelines
will read from the output of the previous
command in the 
.I pipeline .
The leftmost command in a 
.I pipeline 
reads from the terminal if
you neither redirect its 
.I input 
nor give it a filename to use as
.I "standard input" .
Special mechanisms exist for supplying input to commands in shell
scripts (1.5, 3.8).
.IP interrupt
An
.I interrupt
is a signal to a program that is generated by typing ^C. (On older versions
of UNIX the \s-2RUBOUT\s0 or \s-2DELETE\s0 key were used for this purpose.)
It causes most programs to stop execution.
Certain programs, such as the shell and the editors,
handle an 
.I interrupt 
in special ways, usually by stopping what they
are doing and prompting for another command.
While the shell is executing another command and waiting for it
to finish, the shell does not listen to 
.I interrupts.
The shell often wakes up when you hit 
.I interrupt 
because many commands
die when they receive an 
.I interrupt 
(1.8, 3.9).
.IP job
One or more commands
typed on the same input line separated by `|' or `;' characters
are run together and are called a
.I job \&.
Simple commands run by themselves without any `|' or `;' characters
are the simplest 
.I jobs.
.I Jobs
are classified as
.I foreground ,
.I background ,
or
.I suspended
(2.6).
.IP "job\ control"
The builtin functions that control the execution of
jobs are called
.I "job control"
commands.  These are
.I "bg, fg, stop, kill"
(2.6).
.IP "job\ number"
When each job
is started it is assigned a small number called a
.I "job number"
which is printed next to the job in the output of the
.I jobs
command.  This number, preceded by a `%' character, can be used as an argument
to
.I "job control"
commands to indicate
a specific job (2.6).
.IP jobs
The
.I jobs
command prints a table showing
jobs that are either running in the
.I background
or are
.I suspended
(2.6).
.IP kill
A command which sends a
signal
to a job causing it to terminate (2.6).
.IP \&.login
The file
.I \&.login
in your
.I home
directory is read by the shell each time you login to \s-2UNIX\s0
and the commands there are executed.
There are a number of commands which are usefully placed here,
especially
.I set
commands to the shell itself (2.1).
.IP "login\ shell"
The shell that is started on your terminal when you login is called
your
.I "login shell" .
It is different from other shells which you may run (e.g. on
shell scripts)
in that it reads the
.I \&.login
file before reading commands from the terminal and it reads the
.I \&.logout
file after you logout
(2.1).
.IP logout
The
.I logout
command causes a login shell to exit.
Normally, a login shell will exit when you hit control-d
generating an 
.I end\f1-\fPof\f1-\fPfile, 
but if you have set
.I ignoreeof
in you
.I \&.login
file then this will not work and you must use
.I logout
to log off the \s-2UNIX\s0 system (2.8).
.IP \&.logout
When you log off of \s-2UNIX\s0 the shell will execute commands from
the file
.I \&.logout
in your
.I home
directory after it prints `logout'.
.IP lpr
The command
.I lpr
is the line printer daemon.
The standard input of
.I lpr
spooled and printed on the \s-2UNIX\s0 line printer.
You can also give
.I lpr
a list of filenames as arguments to be printed.
It is most common to use
.I lpr
as the last component of a
.I pipeline
(2.3).
.IP ls
The
.I ls
(list files) command is one of the most commonly used \s-2UNIX\s0
commands.
With no argument filenames it prints the names of the files in the
current directory.
It has a number of useful
.I flag
arguments, and can also be given the names of directories
as arguments, in which case it lists the names of the files in these
directories (1.2).
.IP mail
The
.I mail
program is used to send and receive messages from other \s-2UNIX\s0
users (1.1, 2.1), whether they are logged on or not.
.IP make
The
.I make
command is used to maintain one or more related files and to
organize functions to be performed on these files. 
In many ways
.I make
is easier to use, and more helpful than
shell command scripts (3.2).
.IP makefile
The file containing commands for
.I make
is called
.I makefile 
or 
.I Makefile
(3.2).
.IP manual
The 
.I manual 
often referred to is the
`\s-2UNIX\s0 manual'.
It contains 8 numbered sections with a description of each \s-2UNIX\s0
program (section 1), system call (section 2), subroutine (section 3),
device (section 4), special data structure (section 5), game (section 6),
miscellaneous item (section 7) and system administration program (section 8).
There are also supplementary documents (tutorials and reference guides)
for individual programs which require explanation in more detail.
An online version of the 
.I manual 
is accessible through the
.I man
command.
Its documentation can be obtained online via
.DS
man man
.DE
If you can't decide what manual page to look in, try the 
.I apropos (1)
command.
The supplementary documents are in subdirectories of /usr/doc.
.IP metacharacter
.br
Many characters which are neither letters nor digits have special meaning
either to the shell or to \s-2UNIX\s0.
These characters are called
.I metacharacters .
If it is necessary to place these characters in arguments to commands
without them having their special meaning then they must be
.I quoted .
An example of a 
.I metacharacter 
is the character `>' which is used
to indicate placement of output into a file.
For the purposes of the
.I history
mechanism,
most unquoted 
.I metacharacters
form separate words (1.4).
The appendix to this user's manual lists the 
.I metacharacters
in groups by their function.
.IP mkdir
The
.I mkdir
command is used to create a new directory.
.IP modifier
Substitutions with the 
.I history 
mechanism, keyed by the character `!'
or of variables using the metacharacter `$', are often subjected
to modifications, indicated by placing the character `:' after the
substitution and following this with the 
.I modifier 
itself.
The
.I "command substitution"
mechanism can also be used to perform modification in a similar way,
but this notation is less clear (3.6).
.IP more
The program
.I more
writes a file on your terminal allowing you to control how much text
is displayed at a time.
.I More
can move through the file screenful by screenful, line by line,
search forward for a string, or start again at the beginning of the file.
It is generally the easiest way of viewing a file (1.8).
.IP noclobber
The shell has a variable
.I noclobber
which may be set in the file
.I \&.login
to prevent accidental destruction of files by the `>' output redirection
metasyntax of the shell (2.2, 2.5).
.IP noglob
The shell variable
.I noglob
is set to suppress the
.I "filename expansion"
of arguments containing the metacharacters `~', `*', `?', `[' and `]' (3.6).
.IP notify
The
.I notify
command tells the shell to report on the termination of a specific
.I "background job"
at the exact time it occurs as opposed to waiting
until just before the next prompt to report the termination.
The
.I notify
variable, if set, causes the shell to always report the termination
of
.I background 
jobs exactly when they occur (2.6).
.IP onintr
The
.I onintr
command is built into the shell and is used to control the action
of a shell command script when an 
.I interrupt 
signal is received (3.9).
.IP output
Many commands in \s-2UNIX\s0 result in some lines of text which are
called their
.I output.
This 
.I output 
is usually placed on what is known as the
.I "standard output"
which is normally connected to the user's terminal.
The shell has a syntax using the metacharacter `>' for redirecting
the 
.I "standard output" 
of a command to a file (1.3).
Using the
.I pipe
mechanism and the metacharacter `|' it is also possible for
the 
.I "standard output" 
of one command to become the 
.I "standard input" 
of another command (1.5).
Certain commands such as the line printer daemon
.I p
do not place their results on the 
.I "standard output" 
but rather in more
useful places such as on the line printer (2.3).
Similarly the
.I write
command places its output on another user's terminal rather than its
.I "standard output" 
(2.3).
Commands also have a
.I "diagnostic output"
where they write their error messages.
Normally these go to the terminal even if the 
.I "standard output" 
has been sent to a file or another command, but it is possible
to direct error diagnostics along with 
.I "standard output" 
using a special metanotation (2.5).
.IP path
The shell has a variable
.I path
which gives the names of the directories in which it searches for
the commands which it is given.
It always checks first to see if the command it is given is
built into the shell.
If it is, then it need not search for the command as it can do it internally.
If the command is not builtin, then the shell searches for a file
with the name given in each of the directories in the
.I path
variable, left to right.
Since the normal definition of the
.I path
variable is
.DS
path	(. /usr/ucb /bin /usr/bin)
.DE
the shell normally looks in the current directory, and then in
the standard system directories `/usr/ucb', `/bin' and `/usr/bin' for the named
command (2.2).
If the command cannot be found the shell will print an error diagnostic.
Scripts of shell commands will be executed using another shell to interpret
them if they have `execute' permission set.
This is normally true because a command of the form
.DS
chmod 755 script
.DE
was executed to turn this execute permission on (3.3).
If you add new commands to a directory in the 
.I path , 
you should issue
the command 
.I rehash 
(2.2).
.IP pathname
A list of names, separated by `/' characters, forms a
.I pathname.
Each
.I component,
between successive `/' characters, names a directory
in which the next 
.I component 
file resides.
.I Pathnames 
which begin with the character `/' are interpreted relative
to the
.I root
directory in the filesystem.
Other 
.I pathnames 
are interpreted relative to the current directory
as reported by
.I pwd.
The last component of a 
.I pathname 
may name a directory, but
usually names a file.
.IP pipeline
A group of commands which are connected together, the 
.I "standard output"
of each connected to the 
.I "standard input" 
of the next,
is called a
.I pipeline.
The
.I pipe
mechanism used to connect these commands is indicated by
the shell metacharacter `|' (1.5, 2.3).
.IP popd
The
.I popd
command changes the shell's
.I "working directory"
to the directory you most recently left using the
.I pushd
command.  It returns to the directory without having to type its name,
forgetting the name of the current
.I "working directory"
before doing so (2.7).
.IP port
The part of a computer system to which each terminal is
connected is called a
.I port .
Usually the system has a fixed number of
.I ports ,
some of which are connected to telephone lines
for dial-up access, and some of which are permanently
wired directly to specific terminals.
.IP pr
The
.I pr
command is used to prepare listings of the contents of files
with headers giving the name of the file and the date and
time at which the file was last modified (2.3).
.IP printenv
The
.I printenv
command is used
to print the current setting of variables in the environment
(2.8).
.IP process
An instance of a running program is called a 
.I process 
(2.6).
\s-2UNIX\s0 assigns each 
.I process 
a unique number when it is 
started \- called the
.I "process number" .
.I "Process numbers" 
can be used to stop individual 
.I processes
using the 
.I kill
or
.I stop
commands when the
.I processes
are part of a detached
.I background
job.
.IP program
Usually synonymous with
.I command ;
a binary file or shell command script
which performs a useful function is often
called a 
.I program .
.IP prompt
Many programs will print a 
.I prompt 
on the terminal when they expect input.
Thus the editor
`ex (1)' will print a `:' when it expects input.
The shell 
.I prompts
for input with `% ' and occasionally with `? ' when
reading commands from the terminal (1.1).
The shell has a variable
.I prompt
which may be set to a different value to change the shell's main 
.I prompt .
This is mostly used when debugging the shell (2.8).
.IP pushd
The
.I pushd
command, which means `push directory', changes the shell's
.I "working directory"
and also remembers the current
.I "working directory"
before the change is made, allowing you to return to the same
directory via the
.I popd
command later without retyping its name (2.7).
.IP ps
The
.I ps
command is used to show the processes you are currently running.
Each process is shown with its unique process number,
an indication of the terminal name it is attached to,
an indication of the state of the process (whether it is running,
stopped, awaiting some event (sleeping), and whether it is swapped out),
and the amount of \s-2CPU\s0 time it has used so far.
The command is identified by printing some of the words used
when it was invoked (2.6).
Shells, such as the
.I csh
you use to run the 
.I ps 
command, are not normally shown in the output.
.IP pwd
The
.I pwd
command prints the full 
.I pathname 
of the current
.I "working directory" \&.
The
.I dirs
builtin command is usually a better and faster choice.
.IP quit
The
.I quit
signal, generated by a control-\e,
is used to terminate programs which are behaving unreasonably.
It normally produces a core image file (1.8).
.IP quotation
The process by which metacharacters are prevented their special
meaning, usually by using the character `\' in pairs, or by
using the character `\e', is referred to as
.I quotation
(1.7).
.IP redirection
The routing of input or output from or to a file is known
as
.I redirection
of input or output (1.3).
.IP rehash
The
.I rehash
command tells the shell to rebuild its internal table of which commands
are found in which directories in your
.I path .
This is necessary when a new program is installed in one of these
directories (2.8).
.IP "relative pathname"
.br
A
.I pathname
which does not begin with a `/' is called a
.I "relative pathname"
since it is interpreted
.I relative
to the current 
.I "working directory" .
The first
.I component
of such a
.I pathname
refers to some file or directory in the
.I "working directory" ,
and subsequent
.I components
between `/' characters refer to directories below the
.I "working directory" .
.I Pathnames
that are not
.I relative
are called
.I "absolute pathnames"
(1.6).
.IP repeat
The
.I repeat
command iterates another command a specified number of times.
.IP root
The directory
that is at the top of the entire directory structure is called the
.I root
directory since it is the `root' of the entire tree structure of
directories.  The name used in
.I pathnames
to indicate the
.I root
is `/'.  
.I Pathnames 
starting with `/' are said to be
.I absolute
since they start at the
.I root
directory.
.I Root
is also used as the part of a 
.I pathname 
that is left after removing
the 
.I extension .
See
.I filename
for a further explanation (1.6).
.IP \s-2RUBOUT\s0
The \s-2RUBOUT\s0 or \s-2DELETE\s0
key is often used to erase the previously typed character; some users
prefer the \s-2BACKSPACE\s0 for this purpose.  On older versions of \s-2UNIX\s0
this key served as the \s-2INTR\s0 character.
.IP "scratch file"
Files whose names begin with a `#' are referred to as 
.I "scratch files" ,
since they are automatically removed by the system after a couple of
days of non-use, or more frequently if disk space becomes tight (1.3).
.IP script
Sequences of shell commands placed in a file are called shell command 
.I scripts .
It is often possible to perform simple tasks using these 
.I scripts 
without writing a program in a language such as C, by
using the shell to selectively run other programs (3.3, 3.10).
.IP set
The builtin
.I set
command is used to assign new values to shell variables
and to show the values of the current variables.
Many shell variables have special meaning to the shell itself.
Thus by using the 
.I set 
command the behavior of the shell can be affected (2.1).
.IP setenv
Variables in the environment `environ (5)'
can be changed by using the
.I setenv
builtin command (2.8).
The
.I printenv
command can be used to print the value of the variables in the environment.
.IP shell
A 
.I shell 
is a command language interpreter.
It is possible to write and run your own 
.I shell ,
as 
.I shells 
are no different than any other programs as far as the
system is concerned.
This manual deals with the details of one particular 
.I shell ,
called
.I csh.
.IP "shell script"
See
.I script
(3.3, 3.10).
.IP signal
A
.I signal
in \s-2UNIX\s0 is a short message that is sent to a running program
which causes something to happen to that process.
.I Signals
are sent either by typing special
.I control
characters on the keyboard or by using the
.I kill
or
.I stop
commands (1.8, 2.6).
.IP sort
The
.I sort
program sorts a sequence of lines in ways that can be controlled
by argument 
.I flags 
(1.5).
.IP source
The
.I source
command causes the shell to read commands from a specified file.
It is most useful for reading files such as
.I \&.cshrc
after changing them (2.8).
.IP "special character"
.br
See
.I metacharacters
and the
appendix to this manual.
.IP standard
We refer often to the
.I "standard input"
and
.I "standard output"
of commands.
See
.I input
and
.I output
(1.3, 3.8).
.IP status
A command normally returns a
.I status
when it finishes.
By convention a
.I status
of zero indicates that the command succeeded.
Commands may return non-zero 
.I status 
to indicate that some abnormal event has occurred.
The shell variable
.I status
is set to the 
.I status 
returned by the last command.
It is most useful in shell commmand scripts (3.6).
.IP stop
The
.I stop
command causes a
.I background 
job to become 
.I suspended 
(2.6).
.IP string
A sequential group of characters taken together is called a
.I string \&.
.I Strings
can contain any printable characters (2.2).
.IP stty
The
.I stty
program changes certain parameters inside \s-2UNIX\s0 which determine
how your terminal is handled.  See `stty (1)' for a complete description (2.6).
.IP substitution
The shell implements a number of
.I substitutions
where sequences indicated by metacharacters are replaced by other sequences.
Notable examples of this are history 
.I substitution 
keyed by the
metacharacter `!' and variable 
.I substitution 
indicated by `$'.
We also refer to 
.I substitutions 
as
.I expansions
(3.4).
.IP suspended
A job becomes
.I suspended
after a \s-2STOP\s0 signal is sent to it, either by typing a
.I control -z
at the terminal (for
.I foreground
jobs) or by using the
.I stop
command (for
.I background
jobs).  When
.I suspended ,
a job temporarily stops running until it is restarted by either the
.I fg
or
.I bg
command (2.6).
.IP switch
The
.I switch
command of the shell allows the shell
to select one of a number of sequences of commands based on an
argument string.
It is similar to the
.I switch
statement in the language C (3.7).
.IP termination
When a command which is being executed finishes we say it undergoes
.I termination
or
.I terminates.
Commands normally terminate when they read an 
.I end\f1-\fPof\f1-\fPfile
from their 
.I "standard input" .
It is also possible to terminate commands by sending them
an
.I interrupt
or
.I quit
signal (1.8).
The
.I kill
program terminates specified jobs (2.6).
.IP then
The
.I then
command is part of the shell's
`if-then-else-endif' control construct used in command scripts (3.6).
.IP time
The
.I time
command can be used to measure the amount of \s-2CPU\s0
and real time consumed by a specified command as well
as the amount of disk i/o, memory utilized, and number
of page faults and swaps taken by the command (2.1, 2.8).
.IP tset
The
.I tset
program is used to set standard erase and kill characters
and to tell the system what kind of terminal you are using.
It is often invoked in a
.I \&.login
file (2.1).
.IP tty
The word
.I tty
is a historical abbreviation for `teletype' which is frequently used
in \s-2UNIX\s0 to indicate the
.I port
to which a given terminal is connected.  The
.I tty
command will print the name of the
.I tty
or
.I port
to which your terminal is presently connected.
.IP unalias
The
.I unalias
command removes aliases (2.8).
.IP \s-2UNIX\s0
\s-2UNIX\s0 is an operating system on which
.I csh
runs.
\s-2UNIX\s0 provides facilities which allow
.I csh
to invoke other programs such as editors and text formatters which
you may wish to use.
.IP unset
The
.I unset
command removes the definitions of shell variables (2.2, 2.8).
.IP "variable expansion"
.br
See
.I variables
and
.I expansion
(2.2, 3.4).
.IP variables
.I Variables 
in
.I csh
hold one or more strings as value.
The most common use of 
.I variables 
is in controlling the behavior
of the shell.
See
.I path ,
.I noclobber ,
and
.I ignoreeof
for examples.
.I Variables 
such as
.I argv
are also used in writing shell programs (shell command scripts)
(2.2).
.IP verbose
The
.I verbose
shell variable can be set to cause commands to be echoed
after they are history expanded.
This is often useful in debugging shell scripts.
The
.I verbose
variable is set by the shell's
.I \-v
command line option (3.10).
.IP wc
The
.I wc
program calculates the number of characters, words, and lines in the
files whose names are given as arguments (2.6).
.IP while
The
.I while
builtin control construct is used in shell command scripts (3.7).
.IP word
A sequence of characters which forms an argument to a command is called
a
.I word .
Many characters which are neither letters, digits, `\-', `.' nor `/'
form 
.I words 
all by themselves even if they are not surrounded
by blanks.
Any sequence of characters may be made into a 
.I word 
by surrounding it
with `\'' characters
except for the characters `\'' and `!' which require special treatment
(1.1).
This process of placing special characters in 
.I words 
without their special meaning is called
.I quoting .
.IP "working directory"
.br
At any given time you are in one particular directory, called
your 
.I "working directory" .
This directory's name is printed by the
.I pwd
command and the files listed by
.I ls
are the ones in this directory.
You can change 
.I "working directories" 
using
.I chdir .
.IP write
The
.I write
command is an obsolete way of communicating with other users who are logged in to
\s-2UNIX\s0 (you have to take turns typing).  If you are both using display 
terminals, use \fItalk\fP(1), which is much more pleasant.