basic-unix.pdf

BASIC UNIX COMMANDS
Contents
1 Intro 1
2 man - Accessing On-Line Manual Pages 1
3 pwd - Print the Working Directory 2
4 cd - Changing Directory 2
5 ls - Listing the Contents of Directories 2
6 mkdir - Making Directories 3
7 rmdir - Removing Directories 3
8 cp - Copying a File 3
9 cat - Printing Files Onto the Screen 3
10 more - Printing Files One Screen at a Time 4
11 mv - Moving and Renaming Files 4
12 rm - Removing Files and Directories 4
13 chmod - Changing Access Permissions 5
14 diff - Finding the Differences Between Two Files 6
15 grep - Searching for Strings in Files 6
16 wc - Counting Words 6
17 Starting Remote Clients 7
18 Shells 7
19 Files and Pathnames 7
20 Variables and Environments 8
21 Wildcards 9
22 Filename Expansion 9
23 Redirection and Pipes 10
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24 Job Control 10
25 Configuring Your Working Environment 11
26 Mtools — floppy disk tools 12
27 Xman 12
28 Xcalc 12
29 Finger 12
30 Compression Utilities 12
31 Printing and Scanning 12
32 Remote Logging In 12
33 File Transfer 13
1 Intro
Unix is a multi-tasking, multi-user operating system. This means that on any given computer, it appears
as if many things are happening at once and that there may be more than one person logged into the
computer at once. Regardless of which machine you log into in the Institute, you will have access to your
user files and the basic commands will be identical.
The Unix file system is hierarchical. Every file is stored in a directory. A directory can contain many files
or none at all, and may also contain other directories called subdirectories. Unix has three types of files:
Normal Files These are data files which might contain text, source code, executable files, etc.
Special Files These represent physical devices such as terminals and disk drives. The “device drivers”
will translate any references to such files into the hardware instructions needed to carry out the tasks.
Directories These contain “pointers” to normal files, special files and other directories.
File names can be as long as you like, unlike in MS-DOS.
The parent directory of all other directories is called the “root” directory and is denoted by /. Every file
on the system can be accessed by tracing a path from this root directory. See the section on pathnames.
Each user has a “home” directory: this is where you will be located when you login. You are then free to
traverse the directory structure of the Institute and to add to and change the part of the structure which
you own.
Unix commands have the following format:
command [options...] [arguments...]
Where command is the command name, options refer to optional command modifiers (usually prefixed by
a “-”) and arguments are the optional or required command parameters (often file names). Spaces or tabs
are required between commands and options and between options and each argument. Commands must
be typed in the proper case (nearly always lower case).
Although each option to a command may be prefixed by a “-”, with almost all of the standard commands
you may put the options together. For example
command -a -b -c -d
can often be abbreviated as
command -abcd
Again, this is almost always the case - the most notable exceptions are in the GNU commands enscript
and gcc.
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The following are a series of Unix commands which will help you use the computers. They are given in
their most basic form and more information will be available from their on-line manual pages (accessed
through the man command described below).
Each command will be given in a generic form, perhaps with an example of an actual usage. In the
examples, the line alph% will indicate the prompt you see on your screen (which you would not type in if
actually using the command). Note that your prompt may be different.
2 man - Accessing On-Line Manual Pages
The man command looks up the manual page for a command.
The format of man is
man [-k] name...
-k Prints a list of all manual pages containing the keyword name.
Use the -k option if you do not know the name of the command or program.
3 pwd - Print the Working Directory
The pwd command prints the full pathname of your current working directory. The format of pwd is
pwd
For example,
alph% pwd
/home/stlawrence/user/newuser
alph%
The meaning of a full pathname is described in the section on “Filenames and Pathnames”.
4 cd - Changing Directory
The cd command changes the current working directory to the directory specified. The format of cd is
cd [directory]
If you do not specify directory, cd changes to your home directory.
For example,
alph% cd /home/stlawrence/user/newuser
alph% pwd
alph% cd Mail
alph% pwd
/home/stlawrence/user/newuser/Mail
alph% cd
alph% pwd
alph%
5 ls - Listing the Contents of Directories
The ls command lists the contents of one or more specified directories or lists information about one or
more specified files. Normally ls does not list filenames that begin with a dot (“.”). The format of ls is
ls [-aFl] [df(1)] [df(2)] [...] [df(n)]
where df(1..n) is a directory name or a file name.
-a Lists all files, including those that begin with a “.”.
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-F Marks directories with a / and executable files with a *.
-l Produces a longer, more informative listing (see the section on chmod for more information).
For example,
alph% ls
Mail a.out year1 zeta.f zeta.o
alph% ls -F
Mail/ a.out* year1 zeta.f zeta.o
alph%
6 mkdir - Making Directories
The mkdir command makes directories with specified names. The format of the mkdir command is
mkdir directory(1) directory(2)... directory(n)
For example,
alph% ls -F
Mail/ prog/ zeta.f
alph% mkdir thesis zeta
alph% ls -F
Mail/ prog/ thesis/ zeta/ zeta.f
alph%
7 rmdir - Removing Directories
The rmdir command removes empty directories with specified names. The format of the rmdir command
is
rmdir directory(1) directory(2)... directory(n)
The rmdir command will not remove a directory with files in it - for this use the rm -r command, described
later in this section, but be careful!.
For example,
alph% ls -F
Mail/ prog/ thesis/ zeta/ zeta.f
alph% rmdir zeta
alph% ls -F
Mail/ prog/ thesis/ zeta.f
alph%
8 cp - Copying a File
The cp command makes a copy of a file or copies multiple files into a directory. The format of the cp
command is
cp source-file destination-file
or
cp source-file(1) source-file(2)... source-file(n) destination-directory
The first form makes a copy of the file source-file called destination-file and the second copies series of files
source-file(1..n) into directory destination-directory.
alph% ls -F
alpha.f beta.c mydir/ zeta.f
alph% cp zeta.f zeta.f.old
alph% ls -F
alpha.f beta.c mydir/ zeta.f zeta.f.old
alph% cp alpha.f zeta.f mydir
alph% ls -F mydir
4

alpha.f zeta.f
alph%
9 cat - Printing Files Onto the Screen
The cat command prints out the contents of a series of files one after the other. The format of the cat
command is
cat filename(1) filename(2)... filename(n)
For example, to read the “message of the day”,
alph% cat /etc/motd
10 more - Printing Files One Screen at a Time
The more command prints out the contents of named files, one screen full at a time. The format of the
more command is
more filename(1) filename(2)... filename(n)
To quit more, press the q key, to move one line at a time press the RETURN key or the SPACE bar to
move one screen full at a time.
11 mv - Moving and Renaming Files
The mv command changes the name or location of a file or directory. The formats of the mv command are
mv oldfile newfile
mv file(1) file(2)... file(n) directory
mv olddir newdir
For example,
alph% ls -F
Mail/ prog/ zeta/ zeta.f zeta.f.old
alph% mv zeta.f.old zeta-old.f
alph% ls -F
Mail/ prog/ zeta/ zeta.f zeta-old.f
alph% mv zeta.* zeta
alph% ls -F
Mail/ prog/ zeta/
alph% ls -F zeta
zeta:
zeta.f zeta-old.f
alph% mv prog program
alph% ls -F
Mail/ program/ zeta/
alph% mv zeta program
alph% ls -F
Mail/ program/
alph% ls -F program
program:
zeta/
alph%
12 rm - Removing Files and Directories
The rm command removes files and directories. Caution: There is no way to reverse this process (although
see the section on backup). The format of the rm command is
rm [-i] [-r] fd(1) fd(2)... fd(n)
5

where fd(1..n) are files or directories.
-i Inquire before removing a file (“y” to delete, anything else to not delete).
-r Recursively remove a directory and all its contents and subdirectories (Use with extreme care).
For example,
alph% ls
Mail/ prog.f
alph% rm prog.f
alph% ls
Mail/
alph%
13 chmod - Changing Access Permissions
The chmod command changes the “permissions” on a file or directory. It gives or removes access for
another user or group of users to read, change or run one of the files owned by you.
Users on the system fall into three categories:
user You.
group Anyone in the same class as yourself, such as pg 1999, staff or postdoc.
other Anyone who uses the Institute Computers (sometimes called world).
The format of the chmod command is
chmod ugo+-=rwx fd(1) fd(2)... fd(n)
where fd(1..n) may be a file or directory.
where
ugo Specify u (user), g (group) or o (other).
+-= Specify + (add), - (subtract) or = (set).
rwx Specify r (read), w (write) or x (execute).
For files, read permission means you can read the contents of a file, write permission means you can change
the file and execute permission means you can execute the file (if it is executable or it is a shell script).
For directories, read permission means you can see what files are in the directory, write permission means
that you can add to and remove files from the directory and execute means you can access files in that
directory.
Note that to access a file you must have execute permission on all the directories above that on the file
system (including the one in which it is resident). In addition, you must have the appropriate access
permissions for that file.
The permissions on a file may be shown by using the command
alph% ls -lgF
...
-rw-r--r-- 1 newuser pg 1999 1451 Jan 18 11:02 phone
drwxr-xr-x 2 newuser pg 1999 512 Jan 22 12:37 thesis/
...
alph%
There are 10 fields at the start of the entry. The first letter refers to whether the entry is a file (-), directory
(d), or something else (such as s or l). The next letters should be considered in groups of three.
The first group of three refers to the user. The second group of three refers to the members of the group
“pg 1999”. The last group of three refers to world.
Inside each group of three, the three entrys refer to read (r), write (w) and execute (x). A hyphen (-)
indicates something not being set. In the example above all users on the system can read and change into
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the directory called thesis and all users can read the file phone, and in addition the owner can write in
both the thesis directory and can change the file phone.
If, for example, the material in the file phone was personal, it is possible to make sure no one else can read
the file by typing
alph% chmod g-r o-r phone
and the new output of ls -agl would be
alph% ls -agl
...
-rw------- 1 newuser pg 1999 1451 Jan 18 11:02 phone
drwxr-xr-x 2 newuser pg 1999 512 Jan 22 12:37 thesis
...
alph%
in this case g-r refers to “group remove read” and o-r “others remove read”. You could equally use
alph% chmod g+r
to allow anyone in the group “pg 1999” to read the file.
14 diff - Finding the Differences Between Two Files
The diff command compares the contents of two files. The format of diff is
diff file1 file2
For example,
alph% cat dataA
My travel plans are as follows:
Oxford - Heathrow by bus.
Heathrow - Paris by plane.
alph% cat dataB
Travel Plans:
alph% diff dataA dataB
1c1
< My travel plans are as follows:
---
> Travel Plans:
The diff command compares files on a line-by-line basis. A < precedes lines from file1 and a > precedes
lines from file2.
15 grep - Searching for Strings in Files
The grep command scans a file for the occurrence of a word or string and prints out any line in which it
is found. The format of grep is
grep [-i] ’string’ filename(1) filename(2)... filename(n)
-i Ignore case in the search
The single right-quotes around string are necessary only if the string contains non-alphanumeric characters
(such as SPACE, &, etc.).
For example,
alph% cat dataA
alph% grep us dataA
alph% grep ’are as’ dataA
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alph%
16 wc - Counting Words
The wc command counts the lines, words and characters in a file. The format of wc is
wc [-l] [-w] [-c] filename...
-l Prints the number of lines in the files.
-w Prints the number of words in the files.
-c Prints the number of characters in the files.
If no options are specified, wc prints out all three.
For example,
alph% wc dataA
3 16 85 dataA
alph% wc -l dataA
3 dataA
alph%
17 Starting Remote Clients
The most convenient way to connect to remote machines is to use ssh since this gives you a secure encrypted
connection and automatically sets up the display. If however you cannot use ssh then you will have to
setup the DISPLAY variable by hand. For more instructions on this see
http://www.maths.ox.ac.uk/help/faqs/login/.
18 Shells
Once you have understood the level of windows you might then consider exactly how you interface with
the computer to execute the basic Unix commands. This is achieved by something called a shell. A shell is
a program which can run within an xterm. It is not only a command interpreter but can also be used as a
programming language. Inside the shell you type the basic Unix commands listed above. However, many
shells (and there are many of them) have additional features such as automatically finishing the typing
of words, the setting of “aliases” which abbreviate commonly used commands and the ability to keep a
history of commands that you type so that the commands may be used again without retyping them.
There are four shells currently available in the Institute:
• sh. This is the basic Unix shell (the “Bourne” shell) with very few features.
• csh. This is the “C-shell” with extensions based on the C programming language.
• tcsh. This is the “Extended C-Shell” which contains many improvements on csh. This is the default
shell in the Institute which uses the file .cshrc for its configuration.
• bash. This is a hybrid between tcsh and sh which is preferred by some people - the “Bourne Again
Shell”.
More information can be found on these by looking up their appropriate manual pages.
19 Files and Pathnames
When using the ls and cd commands you will have become familiar with the idea of directories and
filenames. An extension of this idea is being able to refer to any file no matter which directory you are in.
So, for instance, when you first login you might type
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alph% pwd
alph% ls -F
Mail/ code/ fortran/ old/ ques.1
alph%
Each level of the directory tree is split by a slash, /. The output of the second command means that there
are four directories called Mail, code, fortran and old, and one file called ques.1.
You can read this file by typing
alph% more ques.1
or by typing
alph% more /home/stlawrence/user/newuser/ques.1
This example demonstrates the use of an absolute pathname. Any pathname beginning with / is an
absolute pathname, anything else is considered relative to the current working directory.
The same result would be obtained by typing
alph% pwd
alph% cd fortran
alph% pwd
/home/stlawrence/user/newuser/fortran
alph% more /home/stlawrence/user/newuser/ques.1
There are some special characters for referring to pathnames.
• . (Single fullstop). Refers to the current directory.
• .. (Two fullstops). Refers to the directory one level immediately up from the current directory.
• ˜newuser (Tilde followed by a user name). Refers to the home directory (the directory first entered
into on login) of a user.
• ˜(Tilde on its own). Refers to your home directory.
So, for instance, to move the file ques.1 from the home directory into the fortran directory, you could type
alph% cd
alph% mv ques.1 fortran
or
alph% cd
alph% cd fortran
alph% mv ../ques.1 .
or even
alph% cd ~/fortran
alph% mv ~/ques.1 .
20 Variables and Environments
One of the features of shells is the ability to set variables and environment variables. Variables and
environment variables are used by the shell and by programs as an indication of a users preference, and
by users as a shorthand for words or lists of words. For example, the lpr command is used to print a
POSTSCRIPT file to a printer. To print the file file.ps to the printer in room G17, you could type
lpr -Plpg17 file.ps
However, when printing a large number of files this could become laborious. When used like this
lpr file.ps
the lpr command checks the environment variable PRINTER; (it is automatically set to your nearest
printer) and then prints to that printer.
So, for instance if you wish to print to a different printer, say lpg17, the command above
alph% lpr -Plpg17 file.ps
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could be achieved by
alph% setenv PRINTER lpg17
alph% lpr file.ps
In addition, commands like dvips check PRINTER as well. Another commonly used variable is DISPLAY,
which is required by X11. These variables are automatically set up upon your login, but can be changed
by using the setenv command.
Variables, like environment variables, are used to store information. When they are set, you give them a
name (like foo), but when they are referenced, you prefix them by a $. For instance, if you were using the
filename shortcontents often, you might use
alph% set foo=shortcontents
alph% echo $foo
shortcontents
alph% cp $foo short
alph% cp $foo contents
alph% lpr -Plpg17 $foo
alph% rm $foo contents
where the last line removes the files $foo (which in this case is shortcontents) and contents.
To list all the environment variables and the variables which are currently set, type setenv or set on a
line by themselves. Often variables and environment variables are set in a shells configuration script. See
the section entitled “Configuring Your Working Environment”.
21 Wildcards
Most shells have a mechanism which indicates groups of letters. For example, to list all the files in a
directory which begin with the letters abc, type
alph% ls abc*
or to list all the four–letter files which end in h, type
alph% ls ???h
The commonly used wildcards are
• * (Asterix). Any character or any number of characters (or no characters at all).
• ? (Question mark). Any single character (not a blank).
Thus,
alph% ls
about above around before
alph% ls a*
about above around
alph% ls a??u*
about around
alph% ls *r*
around before
alph%
Note that wildcard and variable expansion occurs in the shell not in the command that is run (as in DOS).
So it does not work as might be expected. One might niavely think the command
mv *.foo *.bar
would rename each file ending in the suffix .foo to end with the suffix .bar, but in fact it would most likely
result in loss of data. To achieve this end, you could type
alph% foreach f (*.foo)
foreach? mv $f ‘basename $f‘.bar
foreach? end
alph%
For more information on wildcards, see the manual pages for the various shells.
10

22 Filename Expansion
The bash and tcsh shells have the feature of filename expansion. Expansion is carried out by using the
TAB key. For instance,
alph% ls
about above around before
alph% more b{TAB}
will then produce the line
alph% more before
In addition, filename expansion will also work with the names of commands. To use the xmaple package,
you could type
alph% xmap{TAB}
and the word xmaple will appear.
If the letters you have given are not enough to identify the command you mean you will hear a beep. You
need to add another letter and press TAB again. The above example may give such a result since the
commands xmaple-VR4 and xmaple-VR5 may also exist. Alternatively pressing CTRL-d (usually denoted
as ˆD) will list all possible completions from which you can then complete the choice.
23 Redirection and Pipes
Most shells support three standard means of communication with the user: the so called stdin (standard
in), stdout (standard out) and stderr (standard error). stdin is usually the keyboard, both stdout and
stderr are usually the monitor (in the case of X11, stdout and stderr are the window in which the shell is
running). It may be convenient, for instance, to run a program and instead of it printing its results on the
screen to put those results in a file. This is achieved by rerouting stdout.
alph% date
Mon Feb 20 12:22:00 GMT 1995
alph% date > todays.date
alph% cat todays.date
Mon FEB 20 12:22:00 GMT 1995
alph%
In this case, the character > redirects stdout to a file called todays.date. This means that a file called
todays.date will be created (and in some shells erasing any previous contents in that file) and will contain
the output from the command date (note that stderr will still be the monitor or an X term window).
An analogous procedure works to replace the function of typing in a set of values. If you had a program
called addup which took all the numbers on one line of data and added them up, then you could edit a file
called input.deck containing the input.
For example,
alph% cat input.deck
5 and 7 Plus 2
alph% addup < input.deck
The answer is 14
alph%
One could then possibly try
alph% date > todays.date
alph% cat todays.date
Mon Feb 20 12:22:00 pm GMT 1995
alph% addup < todays.date
The answer is 33
alph% addup < todays.date > answer
alph% more answer
The answer is 33
alph%
Note that the shell sees the first word on the line as the command, then anything after the < as the names
of files to provide input, and then anything after the > as files in which to put output.
An analogous procedure to that used above (taking the output from one command and using it immediately
11

as the input of another) is also used in a construction called a pipe.
For example,
alph% date | addup
The answer is 33
alph%
A common usage of this is when running a command and to look at the output one page at a time.
alph% ls -l /usr/bin | more
In this case, ls -l generates a long listing of the files in the directory /usr/bin and then sends the output
to the command more which then prints it on the screen one page at a time.
For more information on redirection and pipes (including many more types of redirection) see the manual
pages of the shells.
24 Job Control
One final aspect of the shells is called job control. It is possible to run one or more than one command at
a time in a given window.
For example, typing the command xclock in an xterm window will bring up a clock. However, you will
notice that in the window you typed xclock the “prompt” does not come back up just yet. By using the
“Skull and Crossbones” (kill) command from the “Window” menu, you can kill the xclock. There will be
a small error in the xterm window, but the prompt will come back. To fix this, you can use an & to send
the job to the background. So, typing xclock & will bring up the clock, run it in the background, and give
you your prompt back. You can run any number of programs (within the machines capacity) from a given
window by using the & character.
So, for example, if you have a program called prime which computes the first 500 prime numbers, but takes
10 minutes to run, you could type the following:
alph% prime > prime.out &
[2] 27103
alph%
and the prime program will run away happily for 10 minutes putting its output in the file prime.out; you
may then continue working on another task (the number 27103 is an indicator of the process number which
would be shown on typing the command ps and the number in square brackets is the job number in this
shell). When it has finished, you will receive a message such as
alph%
[2] prime Done.
alph%
which indicates that the job has finished. To list the current jobs being run from within a shell, type jobs,
alph% jobs
[1] + Running xclock
[2] - Running prime
alph%
Jobs can be put in the foreground and background by using a combination of typing ˆZ (suspend), fg
(foreground) and bg (background). More information on job control can be found in the manual pages of
the shells, and information on how to find out all the processes running at any given time can be found by
typing man ps.
25 Configuring Your Working Environment
There are a number of files which are used to configure your working environment. They are as follows:
.cshrc Used to configure the C Shell and Extended C Shell
.profile Used to configure the Bourne Shell
.bashrc Used to configure the Bourne Again Shell
.emacs Used to configure the emacs program
12

.login Read whenever you login from the terminal and when using telnet
.logout Read whenever you logout from the terminal and when using telnet
.newsrc Configuration file for news readers
.fvwmrc Configuration file for the FVWM Window Manager
.plan A statement about yourself printed whenever someone “fingers” you
.project A one line statement about yourself, printed whenever someone “fingers” you
.xsession Configures your X sessions (e.g. contains information about which programs to run).
They can each be modified by using a text editor. A default account will have the files .cshrc, .xsession,
.login. Each of these files is configured to source additional files with names .cshrc-user, .xsession-user,
.login-user. Never modify the basic files, always put changes in the -user files.
Note that the configuration files .profile, .cshrc and .bashrc need only be present if you are using that
particular shell. In the -user version of these files you might wish to include different aliases and commands
to set environment variables.
26 Mtools — floppy disk tools
The Mtools package allows the transferring of files to and from floppy disks using most Linux PCs. The
commands are similar to those of MS-DOS prefixed by the letter ”m”. Some of the commands are:
mattrib Change MS DOS file attribute flags.
mcd Change MS DOS directory.
mcopy Copy MS DOS files to/from Unix.
mdel Delete an MS DOS file.
mdir Display an MS DOS directory.
mformat Add an MS DOS filesystem to a low-level formatted diskette.
mlabel Make an MS DOS volume label.
mmd Make a MS DOS subdirectory.
mrd Remove a MS DOS subdirectory.
mread Low level read (copy) an MS DOS file to Unix.
mren Rename an existing MS DOS file.
mtype Display contents of an MS DOS file.
mwrite Low level write (copy) a Unix file to MS DOS
More information can be found in the manual page and in the Files Frequently asked Questions.
27 Xman
xman is a program used for reading Unix manual pages (the pages available using the man command).
28 Xcalc
xcalc is a X windows based calculator, usable by the mouse or by typing the numbers in from the keyboard.
29 Finger
finger is available on all the Institutes computers and is used for finding out information about other
users on the Internet. See the manual page for more information.
13

30 Compression Utilities
See the Files Frequently asked Questions
31 Printing and Scanning
See the Printing Frequently asked Questions
32 Remote Logging In
See the Login Frequently asked Questions
33 File Transfer
See the Files Frequently asked Questions
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