csh.g

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.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