An Introduction To UNIX
Pinghua Young
and
Grace Katagiri
October 30, 1995
1 Getting Started with UNIX
1.1 Logging In
What Is Logging In? Logging in is the process by which you identify yourself to a UNIX system.
Before you begin a session at the console, you must use your UNIX account to log in to a workstation
emily3,...,emily14 . Logging in simply is the process through which you tell the system your username and
your password.
Why Doesn't My Password Appear on the Screen? Notice that your password does not appear on
the screen as you type it. This is just added security provided by the UNIX system, so that curious eyes
behind you cannot read your password. Never share your password with anyone, and don't write it down
either. In the EML, if we nd that account information has been shared, the account is immediately and
permanently revoked.
What about Typing Mistakes? If you make a mistake, you must type both your login name and password
again. You are given about three to ve more chances to type them incorrectly depending on the system ,
after which you will be disconnected. Once you successfully log in, the system displays the command-line
prompt and waits for your commands. If you log in from the console meaning you are sitting in front of
an emily in room 616 Evans , you will default to the SunOS Open Windows environment. You can also use
the generic X Windows system if you wish. A windows system is a collection of software that makes it easy
for you to take full advantage of the graphics and windowing capabilities of a workstation. The following
is a sample login session. This is a dial-up from home example, so it doesn't go into a graphical windows
system automatically.
login: pinghua
Password:
Last login: Mon Jan 11 22:45:26 from emily8.Berkeley.
SunOS Release 4.1.1 ECON_SSx 5: Wed Aug 5 12:07:41 PDT 1992
You have new mail.
TERM = vt100
Erase set to Backspace
STUDENT ACCOUNTS MUST BE RENEWED FOR SPRING SEMESTER PRIOR TO
1 19 93. See "news" for details.
Much of the stu included here is taken from various materials gathered over the years. If you want to know more, read
the book C Shell Field Guide by Anderson and Anderson.
1
The workstations in 616 are reserved for tutorials 1 12-14 93
Tu-Fr from 10:00 a.m. - noon.
The air conditioning work in the EML is finished. All the machines
are running as usual.
The EML is reserved for graduate class use M-F 12:00 n. - 5:00 p.m.
Type "help" for help and "news" for news updated Fri 8 Jan 1993 .
Load: 10:46pm up 4 days, 6:26, 0 user, load average: 0.14, 0.02, 0.00
Date: 01 11 93 Time: 22:46:24
Last logout: Mon Jan 11 20:24:52 PST 1993
501 emily10
Notice the prompt is 501 emily10 , which is likely to be di erent from your prompt. Your default prompt
will have a percent sign, which is the prompt for the C shell. Most UNIX systems default to the C
shell. Whenever you see the prompt, you know the system is waiting for further instructions from you.
1.2 Changing Your Password
When? Every once in a while, you de nitely want to change your password to preserve the security of your
account. If you do not change your password for a long time, the system might also refuse your login request.
If you are using a class account, then the rst time you login you should change your assigned password
immediately. You should also use the chfn command to put your real life name and phone number into the
system.
Can I Change My Username? No. Once your choose your username when opening your account, it
cannot be changed easily. Your username is like your personal name, and it will follow you throughout your
career at Berkeley.
Changing Your Password|Your password must not be any word found in the English dictionary, your
username, or any permutation of your name or initials. To change your password, use the command passwd.
Remember, your password does not appear on the screen when you type it.
520 emily8 passwd
Changing NIS password for pinghua on econ.Berkeley.EDU.
Old password:
New password:
Retype new password:
NIS entry changed on econ.Berkeley.EDU
521 emily8
1.3 Logging Out
What Is Logging Out? Logging out ends your session. You must nish each work session by logging out
so that no one else can continue working on the system in your account. If a message on the screen indicates
there are stopped jobs, be sure to `kill' them before logging out. See Section 5.7 for more information on job
control and related commands to kill a job or process.
2
If you are at the console of a Sun, move your mouse pointer to a blank non-window area of the screen, click
with the rightmost button, and select Exit". You will be prompted to con rm Exit". This will log you
out completely. If you are in a terminal emulation character-based, shell, non-windows , just type logout"
or exit" to end your session.
522 emily8 logout
1.4 Getting Information
The UNIX Manual|On the EML system, the complete UNIX reference manual is online the printed
version takes up roughly ve linear feet and costs close to $2,000 . The manual contains descriptions of
the UNIX commands online so that you can refer to it on your screen as needed. Unfortunately, you may
have to dig around to nd just what you're looking for. The man and apropos commands can help you.
The online manual is organized by command; as a novice, you may nd that the di culty is knowing which
command you need to read about. As shown in the following example, you can use the -k option for man
to obtain a list of topics related to a particular keyword. Also, printed copies of part of the UNIX manual
and of the SUN workstation manuals are located in 616 Evans for easy reference.
527 emily8 man man
MAN 1 USER COMMANDS MAN 1
NAME
man - display reference manual pages; find reference pages
by keyword
SYNOPSIS
.
.
.
529 emily8 man -k password
xlock 1 - Locks the local X display until a password is entered.
.IX xlock 1 "" " fLxlock 1 "
xlock 1 - Locks the local X display until a password is entered.
.sp
chkpw 8 - check password file entries against reality
pwget, grget UTIL - get password and group information
crypt, _crypt, setkey, encrypt 3 - password and data encryption
getpass 3V - read a password
getpwaent, getpwanam, setpwaent, endpwaent, fgetpwaent 3 - get password adjun
ct file entry
getpwent, getpwuid, getpwnam, setpwent, endpwent, setpwfile, fgetpwent 3V - ge
t password file entry
passwd 5 - password file
passwd, chfn, chsh 1 - change local or NIS password information
putpwent 3 - write password file entry
pwck 8V - check password database entries
pwdauth, grpauth 3 - password authentication routines
3
pwdauthd 8C - server for authenticating passwords
rfpasswd 8 - change RFS host password
vipw 8 - edit the password file
yppasswd 1 - change your network password in the NIS database
yppasswd 3R - update user password in NIS
yppasswd 5 - NIS password file
yppasswdd, rpc.yppasswdd 8C - server for modifying NIS password file
531 emily8 man passwd
PASSWD 1 USER COMMANDS PASSWD 1
NAME
passwd, chfn, chsh - change local or NIS password informa-
tion
SYNOPSIS
.
.
.
532 emily8
If you are using Open Windows or the X Window System, you can also use the xman command, which has
a much nicer user interface.
2 Working With Files and Directories
2.1 The UNIX File System
What Are Files? You can think of computer les as the folders inside a le cabinet. Each le has a name.
Files are quite important because they allow you to store information for use at a later time. After you nish
your session, the system forgets what you've been doing, unless you save your work in a le to disk.".
How Is a File System Organized? UNIX les are organized into groups called directories they are also
called folders . Directories are les, but instead of containing data or text as other les do, the directory
contains other les. The directories are organized like an inverted tree. The root directory named is at
the top. Note that the root directory in a UNIX system is not equivalent to the PC concept of root." For
PC users, think of your root" directory as being equivalent to the UNIX user's home directory." The
user's home directory usually starts well below the root and other system directories in a UNIX lesystem
tree. Branching out from the root directory are the rest of the directories. Any directory can contain both
directories and other les. Below is a diagram of a simpli ed lesystem. The lesystems on the EML system
are more complex than the ctional one depicted below.
4
|
---------------------------------------------
| | | |
usr etc srv bin
|
------------------------------
| | |
scratch accounts archive
|
------------------------------
| | |
grad undrgrad ucbgrad
|
--------------------------------------
| | |
deng pinghua ddole
|
--------------------------
| | |
bin pub ra
|
---------
| |
tex x11r5
|
-------------------
| |
intro_unix.tex ucblet.tex
2.2 Directories and Paths
The Root Directory|The at the top of the illustration is the root directory. Within this root directory
are: usr, etc, srv, and bin. These les just happen to be directories, which contain their own les. These
directories-within-a-directory are called subdirectories. Thus, srv is a subdirectory of . Every le on the
system is contained in the root directory or in one of its subdirectories.
Your Home Directory|When you rst login to a UNIX system, you are in the directory that holds your
personal les. This directory is called your home directory. In the example above, the home directory of the
user named pinghua is srv accounts grad pinghua. If you are also a graduate student in the Economics
Department, your home directory will be srv accounts grad your username.
Your Current Working Directory|Whenever you use a UNIX system, you are always working in
a speci c directory could be your home directory; could be a subdirectory; could be a public directory
elsewhere on the system . That directory is called the current working directory, or simply, the working
directory. For example, if you were in the usr directory, your working directory would be usr. If you
were in srv accounts projects, then your working directory would be srv accounts projects. Most
commands that operate on directories use the working directory as the default, unless you specify otherwise.
Therefore, it's important to know what the working directory is; to nd out, use the pwd command you
can think of pwd as present working directory :
5
539 emily8 pwd
tmp_mnt srv accounts grad pinghua pub tex
540 emily8
2.3 Finding Out What's in a Directory
The Directory Listing Command|The command for listing the les and subdirectories contained in a
directory is ls. As shown in the following example, di erent information is displayed, depending on what
arguments you use.
542 emily8 ls
ddole intro_unix.tex short_loc_gid.tex.Z
intro_unix.aux local_guide.tex.Z ucblet.tex
intro_unix.dvi multi_ucblet.tex.Z
intro_unix.log multi_ucblet_body.tex.Z
543 emily8 ls usr
5bin custom kvm openwin ucbinclude
5include demo lang pub ucblib
5lib diag lib sccs wp
adm dict local share xpg2bin
app dist lost+found spool xpg2include
bin etc lpp src xpg2lib
blss export man stand
boot games mdec sys
cchelp hosts new tmp
crash include old ucb
544 emily8 ls -l
total 63
-rw------- 1 pinghua 6186 Aug 25 11:43 ddole
-rw------- 1 pinghua 225 Jan 11 17:16 intro_unix.aux
-rw------- 1 pinghua 2800 Jan 11 17:16 intro_unix.dvi
-rw------- 1 pinghua 943 Jan 11 17:16 intro_unix.log
-rw------- 1 pinghua 13745 Jan 11 23:57 intro_unix.tex
-rw-r--r-- 1 pinghua 18401 Mar 12 1992 local_guide.tex.Z
-rw-r--r-- 1 pinghua 1040 May 11 1992 multi_ucblet.tex.Z
-rw------- 1 pinghua 843 May 9 1992 multi_ucblet_body.tex.Z
-rw-r--r-- 1 pinghua 7514 Feb 24 1992 short_loc_gid.tex.Z
-rw-r--r-- 1 pinghua 7483 Oct 10 17:41 ucblet.tex
545 emily8 ls -F
ddole intro_unix.tex short_loc_gid.tex.Z
intro_unix.aux local_guide.tex.Z ucblet.tex
intro_unix.dvi multi_ucblet.tex.Z
intro_unix.log multi_ucblet_body.tex.Z
546 emily8
Dot Files|Within your home directory are some les whose names begin with a dot or period . Most users
don't need to access dot les often. They don't show up on the list supplied when you type the command ls
unless you use the option -a . Because they aren't listed on the screen of your terminal, you can nd other
les more easily. Here is a list of some dot les:
6
.cshrc The system runs the commands in this le each time you start a shell. Usually a good place for alias
commands. See Section 3.1 for more information.
.forward Contains address es where mail for this account should be forwarded, e.g., jbai@athena.mit.edu.
This is useful if you want to receive your mail at a di erent location instead of at the EML system.
Also used with the vacation mail program see help vacmail" .
.login The system runs the commands in this le when you login. Usually you don't need to change anything
here.
.logout The system runs the commands in this le when you logout.
.plan An optional le you create that contains personal or work-related information of an arbitrary nature;
displayed when your username is ngered.
.project An optional le you create that is limited to a short, one line description of your project or course
work; displayed when your username is ngered.
548 emily8 ls -a
. .login .vacation.dir
.. .logout .vacation.msg
... .mailrc .vacation.pag
..forward .mailtool-init .wastebasket
..plan .newsrc .xinitrc.x
..rhosts .newsrc.ucbvax .xinitremoterc
.Data .oldnewsrc .xloadimagerc
.Splus_history .openwin-init .xsession
.Xauthority .openwin-init.BAK .xsession-errors
.Xdefaults.x .openwin-menu News
.Xresources .plan adm
.Xresources.bak .plan.gb bin
.article .plan.hz books
.aut .plan1 calendar
.cetables .plan2 chinese
.cshrc .pnewsexpert lib
.desksetdefaults .pobox login
.fexp .project pub
.forward .rnlast sounds
.gopherrc .rnsoft stat
.history .sh_history tex
.kermrc .signature thesis
.l123set .std.login.mpy tmp
.lastlog .texrc unix
.letter .twmrc
549 emily8
2.4 Changing Directories
You use the cd command to change to another directory. Just cd" by itself always returns you to your
home directory. If you use cd" with one dot . , it means change to your current working directory, and two
dots .. means the parent directory that contains your current working directory. So cd ." is relatively
meaningless, but cd .." will move you up the directory tree, and cd" alone will always take you home.
7
556 emily8 pwd
tmp_mnt srv accounts grad pinghua pub
557 emily8 ls -F
tex x11r5
558 emily8 cd tex
559 emily8 pwd
tmp_mnt srv accounts grad pinghua pub tex
560 emily8 cd ..
561 emily8 pwd
tmp_mnt srv accounts grad pinghua pub
562 emily8
2.5 Creating Directories
For organizational purposes, you may want to create a new subdirectory to hold a group of related les,
as shown in the following sample session. The command for creating a directory is mkdir. After the new
directory is created, you can either create les in that directory or move or copy existing les into it.
566 emily8 mkdir thesis
567 emily8 cd thesis
568 emily8 ls
569 emily8 cd ..
570 emily8
2.6 Removing Directories
You can remove a directory by using the rmdir command. Before you do so, make sure the directory is
empty, i.e., it contains nothing. See Section 2.7 for information about removing les.
572 emily8 ls thesis
573 emily8 rmdir thesis
574 emily8 ls thesis
thesis not found
575 emily8
Absolute Pathnames|To identify a certain le in the le system, you can specify an absolute pathname
by telling UNIX where the le is in relation to the root directory. For example, etc test is a le called
test located within the etc directory under the root directory. The rst signi es the root directory. Each
subsequent directory name is separated by an additional .
For more advanced users: Note that on the EML system, all absolute pathnames on the leserver start with
srv ...". If an absolute pathname starts simply with ", then the pathname refers to a lesystem on the
local workstation for example, tmp" is swap space on the workstation's hard disk, and data1 csrp is a
lesystem that is NFS mounted directly on the workstation, not the leserver.
Another arcane piece of information: Although pwd" returns pathnames beginning with tmp mnt" on the
EML system, you can ignore it in giving absolute pathnames. tmp mnt" is a vestige of the automounting
facility in SunOS, and has no real physical existence.
Even more arcane: srv" is only a pointer to econ", which is the name of our primary leserver. " is
therefore the root directory of the leserver econ". Since we have more than one server, however, we use
8
srv" in pathnames because it always points to the correct server, even though les may move back and
forth. For example, srv scratch" is equivalent to econ scratch" when logged into the econ" leserver.
On the emlab" server, srv scratch" is equivalent to emlab scratch".
'Nu said.
Relative Pathnames|Besides identifying a le by its absolute pathname, you can use a relative pathname.
That is, you can tell UNIX where the le is in relation to the working directory. Suppose we are in Pinghua's
home directory that contains a subdirectory called pub. pub contains a le called test. Instead of using
absolute pathname like srv accounts grad pinghua pub test, we can simply use pub test to refer
to it.
581 emily8 pwd
tmp_mnt srv accounts grad pinghua
582 emily8 ls pub
test tex x11r5
583 emily8 cat pub test
This is a test file.
584 emily8
Like one dot . and two dots .. , there is also a shorthand for referring to home directories. ~ denotes your
own home directory, while ~username denotes username's home directory. For example, ~pinghua refers
to Pinghua's home directory, so to go to his home directory from your home directory, you can simply type
cd ~pinghua.
2.7 Handling Files
Copying Files|The command to copy les is cp. Its rst argument is the source le, that is, the le you
are copying. Its second argument is either the name you want for the new, copied le or the destination
directory. If a directory is given as the second argument, the le is copied into that directory with the same
le name. You can also use wildcards to copy a group of les. See the end of this sub-section for more
information about wildcard characters.
Warning: When you use the cp command, the system doesn't check to see if a le already has the name
you chose for the destination le. If that le name already exists, the system removes the existing le before
it copies the le you speci ed. If you want the system to ask you for con rmation, use cp -i instead of
simply cp.
601 emily8 ls
ddole intro_unix.tex short_loc_gid.tex.Z
intro_unix.aux local_guide.tex.Z ucblet.tex
intro_unix.dvi multi_ucblet.tex.Z
intro_unix.log multi_ucblet_body.tex.Z
602 emily8 cp intro_unix.tex intro_unix_bak.tex
603 emily8 ls
ddole intro_unix.tex multi_ucblet_body.tex.Z
intro_unix.aux intro_unix_bak.tex short_loc_gid.tex.Z
intro_unix.dvi local_guide.tex.Z ucblet.tex
intro_unix.log multi_ucblet.tex.Z
604 emily8 cp intro_unix ..
cp: intro_unix: No such file or directory
9
605 emily8 cp intro_unix.tex ..
606 emily8 ls ..
intro_unix.tex test tex x11r5
607 emily8
Moving Files or Changing Their Names|The command for both moving a le from one directory to
another and renaming a le is mv. Its rst argument is the source le, and its second argument can be
either the destination directory or the new name of the le.
608 emily8 ls
ddole intro_unix.tex multi_ucblet_body.tex.Z
intro_unix.aux intro_unix_bak.tex short_loc_gid.tex.Z
intro_unix.dvi local_guide.tex.Z ucblet.tex
intro_unix.log multi_ucblet.tex.Z
609 emily8 mv intro_unix_bak.tex tmp
610 emily8 ls intro_unix_bak.tex
intro_unix_bak.tex not found
611 emily8 ls tmp intro_unix_bak
tmp intro_unix_bak not found
612 emily8 ls tmp intro_unix_bak.tex
tmp intro_unix_bak.tex
613 emily8 mv intro_unix.log garbage
614 emily8 ls intro_unix.log garbage
intro_unix.log not found
garbage
615 emily8
Referring to Groups of Files|There are some so-called wildcard characters of which you should be
aware. They provide you with a powerful way of referring to a group of les easily. One is the character *,
which means any string of characters. Another one is ?, which refers to any single character. For example:
616 emily8 ls
ddole intro_unix.tex short_loc_gid.tex.Z
garbage local_guide.tex.Z ucblet.tex
intro_unix.aux multi_ucblet.tex.Z
intro_unix.dvi multi_ucblet_body.tex.Z
617 emily8 ls *.tex
ddole intro_unix.tex ucblet.tex
618 emily8 ls *.Z
local_guide.tex.Z multi_ucblet_body.tex.Z
multi_ucblet.tex.Z short_loc_gid.tex.Z
619 emily8 ls intro_unix.???
intro_unix.aux intro_unix.dvi intro_unix.tex
10
620 emily8 ls intro_unix.*
intro_unix.aux intro_unix.dvi intro_unix.tex
621 emily8 ls intro_unix.?
ls: No match.
622 emily8
Creating and Removing Files|There are a lot of ways to create les. An obvious way is to use an editor
such as vi, emacs, or jove, etc. You can also use UNIX's powerful output redirection to create a le. See
Section 4 for more information about this and other powerful tips and tricks like pipes.
To remove a le, use the rm command. Be careful with this command. Once the le is removed, it's gone
forever. You can't use Norton Utilities to get it back. Just to be on the safer side, use rm -i instead of plain
rm. Or better yet, put alias rm rm -i into your .cshrc le.
2.8 Browsing through Files
Looking at Files One Screenful at a Time|You can use the more, less, or page commands to display
a screenful of the le at a time. To display the next screenful, press the space bar. Type man more, man
less for more information.
The UNIX command cat also allows you to view les on your screen, but it won't show one screenful at a
time. However, you can use it for other purposes. For example, if you want to append le2 to le1, simply
type cat le2 le1. For more information, type man cat.
Looking at the Beginning or End of a File|You use the commands head or tail to display the
beginning or the end of a le. The default is the rst 10 or the last 10 lines, but you can specify how many
lines you want, as shown in the following example.
649 emily8 head ~ .cshrc
source the standard .cshrc file
source usr local skel std.cshrc
personal customization
set path = $HOME bin ~choices bin $HOME unix mac moby pbmplus bin tmp_mnt mob
y b tiff sun4_sunos4.1.1 bin $path usr demo SOUND usr local x11r5 games usr e
tc
source $HOME ... .cshrc
umask 077
650 emily8 tail ~ .cshrc
source the standard .cshrc file
source usr local skel std.cshrc
personal customization
set path = $HOME bin ~choices bin $HOME unix mac moby pbmplus bin tmp_mnt mob
y b tiff sun4_sunos4.1.1 bin $path usr demo SOUND usr local x11r5 games usr e
tc
source $HOME ... .cshrc
umask 077
651 emily8 tail -5 ~ .cshrc
11
personal customization
set path = $HOME bin ~choices bin $HOME unix mac moby pbmplus bin tmp_mnt mob
y b tiff sun4_sunos4.1.1 bin $path usr demo SOUND usr local x11r5 games usr e
tc
source $HOME ... .cshrc
umask 077
652 emily8
2.9 Searching and Comparing Files
Searching for Text|You can use the grep command to search for a string in a text le. This is actually
a very powerful utility, and you might want to learn more about it by typing man grep.
629 emily8 grep grep intro_unix.tex
bf Searching for Text ---You can use the bf grep command to search for
you might want to learn more about how to use it by typing bf man grep .
630 emily8 grep UNIX intro_unix.tex
title An Introduction To UNIX
section Beginning UNIX
you must use your UNIX account to log in to the computer---Emily1
added protection provided by the UNIX system so that curious eyes
bf The UNIX Manual ---On EML UNIX System the reference manual is online
in the computer . The manual contains descriptions of the UNIX commands online
so that you can refer to it on your screen as needed. Unfortunately, you may
UNIX manuals and of the SUN workstation manuals are located in 616 Evans
subsection The UNIX File System
bf How Is a File System Organized? UNIX files are organized into groups
EML UNIX computers are more complex than the fictional one depicted below.
bf Your Home Directory ---When you first login to a UNIX system, you are
bf Your Current Working Directory ---Whenever you are using a UNIX system,
can specify an absolute pathname by telling UNIX where the file is in relation
you can use a relative pathname. That is, you can tell UNIX where the file
use UNIX's powerful output redirection to create a file. See later sections
631 emily8
Comparing Files|The di and cmp commands allow you to compare two les to see if they are identical.
The di command displays the actual lines in each le that di er, whereas the cmp command lists the
location in the rst le where the rst di erence between them occurs. If the two les are identical, the
prompt reappears. For more information type man di or man cmp.
633 emily8 cp intro_unix.tex garbage
overwrite garbage? y
634 emily8 diff intro_unix.tex garbage
635 emily8 cmp intro_unix.tex garbage
636 emily8
2.10 Handling File Security: File Access Permissions
UNIX Security|UNIX gives you the ability to protect your work as you see t. You decide what you can
12
do to your work, and what others can do to it. The UNIX security system allows you some control over who
can see, alter, and use your les and directories.
In the UNIX environment, those who may access a particular le or directory are divided into three classes,
as shown in the following:
Class of User De nition
owner the user who owns the le directory
group the group of users who share access to a le. Every user
belongs to a group. In general, graduate students belong to
the same group. To see what group you are in, type groups.
other all other users.
Each le or directory has a set of permissions that control access to it. For each class of users above, there
are three permissions that may be granted in relation to each le or directory. These are shown here.
Permission File Directory
read r Allows you to read the le Allows you to list the contents of of the directory
write w Allows you to create, delete, Allows you to create and delete les in the directory,
and modify the le. since this requires writing to the actual directory.
execute x Allows you to run a le. Allows you to list only the les whose names you specify,
not the directory itself.
Finding Out What Permissions a File Has|When you create a le or a directory, it is assigned a
default set of permissions, which you can change. With the command ls -l, you can see the permissions
associated with a particular le as the rst 10 characters on each line of the output. Be sure to use the
correct absolute or relative pathname for the le.
671 emily8 ls -l
total 23
-rw------- 1 pinghua 20016 Jan 12 01:05 intro_unix.tex
-rw-r--r-- 1 pinghua 21 Jan 12 00:35 test
drwxr-sr-x 2 pinghua 512 Jan 12 01:45 tex
drwxr-sr-x 2 pinghua 512 Aug 3 17:34 x11r5
672 emily8
The rst character indicates whether this le is a directory d or just a regular le - . The next three
groups consisting of three characters each 9 characters total are the permissions granted for the owner,
group, and other classes, respectively. A permission is granted if the letter is present, and not granted if the
, is there instead.
Making Security Changes|You can change the permission modes using the chmod command. The plus
+ sign indicates access addition and minus , indicates access deletion. For more information type man
chmod and man umask.
674 emily8 ls -l
total 23
-rw------- 1 pinghua 20016 Jan 12 01:05 intro_unix.tex
-rw-r--r-- 1 pinghua 21 Jan 12 00:35 test
drwxr-sr-x 2 pinghua 512 Jan 12 01:45 tex
drwxr-sr-x 2 pinghua 512 Aug 3 17:34 x11r5
13
675 emily8 chmod go-r test
676 emily8 ls -l test
-rw------- 1 pinghua 21 Jan 12 00:35 test
677 emily8 chmod g+rw intro*
678 emily8 ls -l intro*
-rw-rw---- 1 pinghua 20016 Jan 12 01:05 intro_unix.tex
679 emily8
3 The Shell Program
About the Shell Program|As soon as you log in, the shell program is activated. Providing the interface
between you and the system, the shell is the program that reads your commands and invokes other programs
to carry them out. The default shell that you will be using is the bin csh or C shell. You can also change
it to bin tcsh by using the chsh command. The shell program bin tcsh is an enhanced version of
bin csh, allowing you to call back previous commands and edit them. For more information on changing
your default shell program, type man chsh. Warning: do not change your default shell unless you really
know what you are doing.
When the shell is ready for your command, it displays its prompt. In this document, we are using Pinghua's
own prompt 680 emily8 in the sample sessions. You can change your default prompt as shown later on
in this section.
3.1 Customizing Your Session: De ning Your Shell Environment
UNIX allows you to customize your interaction with the shell in many ways. You can:
create abbreviations for les or directories or lengthy commands;
determine the directories the shell uses to search for the programs and commands to run;
create the prompt the shell uses when it interacts with you, and
have UNIX try to set your terminal type every time you dial in from home, without having to type
the command yourself.
3.1.1 Shell Variables
Setting Shell Variables|Shell variables help determine how the shell program interacts with you. You
can create your own shell variable and assign it a value with the set command. And you can use the variable
in a command line by pre xing the variable name with $.
521 emily5 set workdir = srv accounts projects choices
522 emily5 echo $workdir
srv accounts projects choices
523 emily5 ls $workdir
News bin hlogit sst_docu workshop
README crane nag tar x
14
524 emily5 unset workdir
525 emily5
If you want to use the shell variable every time you interact with the csh or tcsh shell, add the command
line to your .cshrc le. This is the C Shell Runtime Commands le, a dot le in your home directory.
Looking at Shell Variables|You can also use the set command to see shell variables and their values.
525 emily5 set
_etc
_mpath usr local x11 man: usr local ow3 man
_wpath usr local x11 bin usr local ow3 bin
_x11 usr local x11
addsuffix
argv
cwd srv accounts grad pinghua pub tex
echo_style bsd
edit
filec
gid 130
history 500
home srv accounts grad pinghua
hostname emily5
ignoreeof
mail 2 usr spool mail pinghua_young etc motd usr msgs
mdir usr spool mail
noclober
notify
old srv accounts grad pinghua
path srv accounts grad pinghua bin srv accounts projects choices bin
srv accounts grad pinghua unix mac moby pbmplus bin
tmp_mnt moby b tiff sun4_sunos4.1.1 bin
usr local x11 bin usr local ow3 bin usr local bin usr lang usr ucb bin us
r bin usr hosts . usr app bin usr local wp51 wpbin usr local TeX bin usr de
mo SOUND usr local x11r5 games usr etc
prompt ! emily5
prompt2 loop:
prompt3 CORRECT R y|n|e ?
savehist 500
shell bin tcsh
shlvl 1
status 0
tcsh 6.02.00
term xterm
tperiod 5
tty ttyp1
uid 305
user pinghua
version tcsh 6.02.00 Cornell 92 05 15 options 8b,nls,dl,al,dir
window_menu
526 emily5
15
Some Important Shell Variables|A few shell variables have special meaning to the shell program. By
assigning values to these variables, you customize the standard manner in which the shell executes your
commands. Those covered here are: path, prompt, history and term.
About the Path Shell Variable|One of the most important shell variables is the path shell variable.
The value for the path shell variable is a list of directories enclosed in parentheses. This list of directories is
called your search path. UNIX searches these directories when it looks for a program that you specify in a
command line. If a program is in your search path, you can type just the name of the program. Otherwise,
you have to specify its absolute or relative pathname.
Suppose your search path is:
bin usr local x11r5 bin usr bin
Then whenever you type a program name or command, the shell looks rst in the bin directory, second in
the directory usr local x11r5 bin and nally in the directory usr bin. It keeps looking until it either
nds the program or command with that name or nishes looking through all the directories in your search
path. If it cannot nd it among the directories listed in your search path, it's going to give you the error
message of Command not found.
526 emily8 nslookup
nslookup: Command not found.
527 emily8 set path = usr etc $path
528 emily8 nslookup
Default Server: econ.Berkeley.EDU
Address: 128.32.105.1
exit
529 emily8
The procedure shown in this example only adds one directory to your search path for your present interaction
with the current shell. If you nd that you often use a program or command not speci ed in your default
search path, you can edit or add the command line set path = new search directory $path to your
.cshrc le. To nd out the value of your path shell variable, simply type echo $path at your shell prompt.
About the Prompt Shell Variable|The value for the prompt shell variable is what displays as the shell's
prompt. You can customize your shell prompt by using the procedure shown in the following example.
532 emily8 set prompt="what now? "
what now? ls
intro_unix.tex multi_ucblet.tex short_loc_gid.tex
local_guide.tex multi_ucblet_body.tex ucblet.tex
what now?
In the tcsh, to change the prompt permanently, add the command line set prompt = your desired
prompt" in your .cshrc le.
About the History Shell Variable|The value associated with the history shell variable is the number
of the commands last entered, which UNIX will save when you use the history command. See Keeping
Command History later in Section 6. To set the number of commands that UNIX will save for subsequent
sessions, add the command line set history = 500 in your .login le 500 is just an example . In this case,
UNIX will remember 500 commands for you, but only for the current work session. Once you logout, those
500 commands won't be remembered. To ask UNIX to keep the 500 commands from the previous session
16
available to you for the current session, add set savehist = 500 in your .cshrc le. For more information
read man csh.
About the Term Shell Variable|The value associated with the term shell variable is the type of terminal
you are using. This is important when you are dialing in from home. If you are using vt100 or vt102
emulation mode with your PC or Mac communication software, then you probably don't have to set this
variable explicitly. But if you are using some other emulation mode, then you have to set the terminal type
explicitly to the type you are using. Otherwise, programs such as text editors won't work properly.
3.1.2 Modifying the .login and .cshrc Files
In general, you should be very careful when you start modifying these two les. Make sure you know what
you are doing, and remember the line s you are adding. If it doesn't work, put in front of the line so
that it won't be executed. Warning: do not blindly copy lines from someone else's dot les, or edit your dot
les yourself unless you know exactly what you are doing. Otherwise you will come to grief. Additionally,
never put another user's directory into a set path" statement. Think about it: you'll be sorry when that
account is closed.
The di erence between .login and .cshrc les is: when you login, UNIX executes the .cshrc le rst and
then .login. UNIX also executes your .login le once, whereas it executes your .cshrc le whenever you
start a subshell.
After you add or modify command lines in the .cshrc or .login les, UNIX won't run the commands
immediately. Unless you use the source command, you have to logout and then login in order for the
changes to take e ect.
532 emily8 source .login
533 emily8 source .cshrc
3.1.3 Environment Variables
These are similar to shell variables, but other programs besides the shell use their values. Typically, these
environment variable names are all uppercase. An example of an environment variable is PRINTER. The
value associated with this environment variable determines the default printer. The commands to set, unset,
and look at environment variables are slightly di erent from those used with shell variables. Like shell
variables, the command lines can be changed or added to your .login or .cshrc le.
537 emily8 setenv PRINTER lp1
538 emily8 unsetenv PRINTER lp1
539 emily8 printenv
HOME= srv accounts grad pinghua
SHELL= bin tcsh
TERM=vt100
USER=pinghua
PATH= srv accounts grad pinghua bin: srv accounts projects choices bin:
srv accounts grad pinghua unix mac: usr local x11 bin: usr local ow3 bin:
usr local bin: usr lang:
usr ucb: bin: usr bin: usr hosts:.: usr app bin: usr local wp51 wpbin: usr loca
l TeX bin: usr demo SOUND: usr local x11r5 games: usr etc
LOGNAME=pinghua
SHLVL=1
PWD= srv accounts grad pinghua pub tex
17
HOST=emily8.Berkeley.EDU
HOSTTYPE=sun4
WPTERM51=sunshell
LD_LIBRARY_PATH= usr local x11 lib: usr local ow3 lib
HELPPATH= usr local x11 lib help: usr local ow3 lib help
XFILESEARCHPATH= usr local x11 lib X11 T NC: usr local x11 lib X11 T N: usr
local ow3 lib T NS
OPENWINHOME= usr local ow3
MANPATH= usr local x11 man: usr local ow3 man: usr local man: usr lang man: usr
man: usr app man
PAGER=more
EXINIT=set redraw
TERMINFO= usr share lib local terminfo
TERMPATH= usr local etc termcap.local: etc termcap
GNUTERM=tek40
TERMCAP=d0|vt100|vt100-am:do=^J:co80:li36:cl=50 E ;H E 2J:le=^H:bs:am:cm=5 E
id;dH:nd=2 E C:up=2 E A:ce=3 E K:cd=50 E J:so=2 E 7m:se=2 E m:us=2 E 4;1m:ue=2
E m:md=2 E 1m:mr=2 E 7m:mb=2 E 5m:me=2 E m:is= E ?7h E 1;24r E 24;1H:rf= usr li
b tabset vt100:rs= E E ?3l E ?4l E ?5l E ?7h E ?8h:ks= E ?1h E=:ke= E ?1l E :ku
= EOA:kd= EOB:kr= EOC:kl= EOD:kb=^H:ho= E H:k1= EOP:k2= EOQ:k3= EOR:k4= EOS:pt:s
r=5 EM:vt3:xn:ti= E ?7l:te= E ?7h:sc= E7:rc= E8:cs= E id;dr:
MAIL= usr spool mail pinghua
VISUAL= usr ucb vi
NAME=Pinghua Young
ORGANIZATION=University of California at Berkeley
540 emily8
3.2 Creating Shorthand Names for Commands: Aliases
Aliases allow you to create shorthand names for frequently used or lengthy command lines, and to create
modi ed versions of existing system commands customizing" commands . When the alias appears in the
command line that the shell reads, its text is replaced by the de nition of the alias. You use the alias
command to create aliases and the unalias command to delete them. To display a de nition of an alias,
just type alias and the name.
541 emily8 alias a alias
542 emily8 a f finger
543 emily8 a bai f jushan@athena.mit.edu
544 emily8 bai
athena.mit.edu
Login name: jbai In real life: Jushan Bai
Nickname: Home phone:
Office: E52-274B Office phone: 617-253-6217
Electronic mail address: jbai@ATHENA.MIT.EDU
545 emily8 alias bai
finger jushan@athena.mit.edu
546 emily8
Arguments in Aliases|Unless you specify otherwise, the C shell assumes that all arguments come at the
end of the alias de nition. For example, suppose cx is an alias for chmod +x. Then cx * would expand
to chmod +x *.
18
What if we want arguments placed somewhere besides at the end of an alias de nition? For example, let's
take a look the nd command. To locate the le intro unix.tex starting from our home directory, we type
521 cox find ~ -name intro_unix.tex -print
srv accounts grad pinghua pub tex intro_unix.tex
522 cox
We want to create an alias called loc that takes a lename as an argument to the nd command. A way to
do this is
alias loc 'find ~ -name !* -print'
To avoid accidental removal of les, we strongly suggest that you put the following aliases in your .cshrc
le:
alias rm rm -i
alias cp cp -i
alias mv mv -i
You might also want to add alias ls ls -F to your .cshrc le.
4 Input Output Redirection and Pipes
4.1 Sending Results Where You Want Them: Output Redirection
Many UNIX commands, such as who, ls, and date, normally display their output on the terminal screen.
Once it is overwritten or scrolls o the screen, you must execute the command again to view it unless, of
course, you are using a windows system that allows you to scroll back . Output redirection lets you save
output in a le for later reference or for use as the input to another program.
Standard Output|We refer to the output that normally appears on the screen excluding error messages
as standard output. We may send standard output to a le using output redirection. For example, The
command who users.list saves the output from who in a le called users.list.
532 cox ls users.list
users.list not found
533 cox who users.list
534 cox cat users.list
mcfadden console Jan 13 09:47
goldman ttyp0 Dec 11 11:52
goldman ttyp1 Dec 14 09:17
goldman ttyp2 Nov 23 15:19
goldman ttyp3 Dec 1 09:02
goldman ttyp4 Jan 12 10:53
goldman ttyp5 Jan 4 09:08
goldman ttyp6 Jan 4 11:36
mcfadden ttyp7 Jan 13 09:48
mcfadden ttyp8 Jan 13 09:48
goldman ttyp9 Jan 15 12:01
goldman ttypa Jan 14 11:56
19
mcfadden ttypb Jan 14 15:14
pinghua ttypc Jan 17 17:21 econnet.Berkeley
535 cox
We may say that redirects the output. Notice that in the above sample session, the le users.list did not
exist. The C shell simply created it and put who's output there. If the le users.list had existed before
we issued who users.list command, its previous contents would have been destroyed. If you don't want
this to happen, use instead of . For example,
536 cox ps -uax | grep pinghua users.list
537 cox cat users.list
mcfadden console Jan 13 09:47
goldman ttyp0 Dec 11 11:52
goldman ttyp1 Dec 14 09:17
goldman ttyp2 Nov 23 15:19
goldman ttyp3 Dec 1 09:02
goldman ttyp4 Jan 12 10:53
goldman ttyp5 Jan 4 09:08
goldman ttyp6 Jan 4 11:36
mcfadden ttyp7 Jan 13 09:48
mcfadden ttyp8 Jan 13 09:48
goldman ttyp9 Jan 15 12:01
goldman ttypa Jan 14 11:56
mcfadden ttypb Jan 14 15:14
pinghua ttypc Jan 17 17:21 econnet.Berkeley
pinghua 2934 0.0 0.3 32 208 pc S 18:00 0:00 grep pinghua
pinghua 2831 0.0 0.8 360 524 pc S 17:21 0:02 -tcsh tcsh
pinghua 2892 0.0 0.0 184 0 pc TW 17:35 0:03 vi intro_unix.tex
pinghua 2933 0.0 0.7 200 436 pc R 18:00 0:00 ps -uax
538 cox
In the above sample session, the output from ps -aux j grep pinghua is appended to the le users.list.
Safer Redirection and Appending|Redirection can easily destroy a valuable le accidentally. To avoid
this, the C shell provides a protective version of redirection and appending. This works as follows:
It does not allow redirection if the le already exists.
It does not allow appending if the le does not already exist.
This keeps you from accidentally destroying a valuable le or creating a new le just because of absent-
mindedness or typing errors. The command set noclobber activates this additional protection.
539 cox set noclobber
540 cox who users.list
users.list: File exists.
541 cox date status
status: No such file or directory.
542 cox
You may want to put set noclobber in your .cshrc le. Note: in the EML system, noclobber" is already
set in the system default standard .cshrc le for all accounts. To overwrite this extra protection, use !
and ! instead of and when redirecting and appending standard output.
20
4.2 Getting the Input You Need: Input Redirection
You can redirect input as well as output. For example, the mail command normally reads input from your
terminal as shown in the sample session below.
546 cox mail pinghua@econ
Subject: test
This is a test. Please ignore.