What is UNIX?
UNIX is an operating system which was first developed in the 1960s, and has been under constant development ever since. By operating system, we mean the suite of programs which make the computer work. It is a stable, multi-user, multi-tasking system for servers, desktops and laptops.
UNIX Systems also have a graphical user interface (GUI) similar to Microsoft Windows which provides an easy to use environment. However, knowledge of UNIX is required for operations which aren’t covered by a graphical program, or for when there is no windows interface available, for example, in a telnet session.
Types of UNIX
There are many different versions of UNIX, although they share common similarities. The most popular varieties of UNIX are Sun Solaris, GNU/Linux, and MacOS X.
The UNIX Operating System
The UNIX operating system is made up of three parts; the kernel, the shell and the programs.
The kernel
The kernel of UNIX is the hub of the operating system: it allocates time and memory to programs and handles the filestore and communications in response to system calls.
As an illustration of the way that the shell and the kernel work together, suppose a user types rm myfile (which has the effect of removing the file myfile). The shell searches the filestore for the file containing the program rm, and then requests the kernel, through system calls, to execute the program rm on myfile. When the process rm myfile has finished running, the shell then returns the UNIX prompt % to the user, indicating that it is waiting for further commands.
The shell
The shell acts as an interface between the user and the kernel. When a user logs in, the login program checks the username and password, and then starts another program called the shell. The shell is a command line interpreter (CLI). It interprets the commands the user types in and arranges for them to be carried out. The commands are themselves programs: when they terminate, the shell gives the user another prompt (% on our systems).
The adept user can customise his/her own shell, and users can use different shells on the same machine. Staff and students in the school have the tcsh shell by default.
The tcsh shell has certain features to help the user inputting commands.
Filename Completion – By typing part of the name of a command, filename or directory and pressing the [Tab] key, the tcsh shell will complete the rest of the name automatically. If the shell finds more than one name beginning with those letters you have typed, it will beep, prompting you to type a few more letters before pressing the tab key again.
History – The shell keeps a list of the commands you have typed in. If you need to repeat a command, use the cursor keys to scroll up and down the list or type history for a list of previous commands.
Files and processes
Everything in UNIX is either a file or a process.
A process is an executing program identified by a unique PID (process identifier).
A file is a collection of data. They are created by users using text editors, running compilers etc.
Examples of files:
a document (report, essay etc.)
the text of a program written in some high-level programming language
instructions comprehensible directly to the machine and incomprehensible to a casual user, for example, a collection of binary digits (an executable or binary file);
a directory, containing information about its contents, which may be a mixture of other directories (subdirectories) and ordinary files.
The Directory Structure
All the files are grouped together in the directory structure. The file-system is arranged in a hierarchical structure, like an inverted tree. The top of the hierarchy is traditionally called root (written as a slash / )
UNIX Knowledge For Software Testers
UNIX OS Knowledge for Software Testers
UNIX Commands
Contents
cat — for creating and displaying short files
chmod — change permissions
cd — change directory
cp — for copying files
date — display date
echo — echo argument
ftp — connect to a remote machine to download or upload files
grep — search file
head — display first part of file
ls — see what files you have
lpr — standard print command (see also print )
more — use to read files
mkdir — create directory
mv — for moving and renaming files
ncftp — especially good for downloading files via anonymous ftp.
print — custom print command (see also lpr )
pwd — find out what directory you are in
rm — remove a file
rmdir — remove directory
rsh — remote shell
setenv — set an environment variable
sort — sort file
tail — display last part of file
tar — create an archive, add or extract files
telnet — log in to another machine
wc — count characters, words, lines
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cat
This is one of the most flexible Unix commands. We can use to create, view and concatenate files. For our first example we create a three-item English-Spanish dictionary in a file called “dict.”
% cat >dict
red rojo
green verde
blue azul
<control-D>
%
<control-D> stands for “hold the control key down, then tap ‘d'”. The symbol > tells the computer that what is typed is to be put into the file dict. To view a file we use cat in a different way:
% cat dict
red rojo
green verde
blue azul
%
If we wish to add text to an existing file we do this:
% cat >>dict
white blanco
black negro
<control-D>
%
Now suppose that we have another file tmp that looks like this:
% cat tmp
cat gato
dog perro
%
Then we can join dict and tmp like this:
% cat dict tmp >dict2
We could check the number of lines in the new file like this:
% wc -l dict2
8
The command wc counts things — the number of characters, words, and line in a file.
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chmod
This command is used to change the permissions of a file or directory. For example to make a file essay.001 readable by everyone, we do this:
% chmod a+r essay.001
To make a file, e.g., a shell script mycommand executable, we do this
% chmod +x mycommand
Now we can run mycommand as a command.
To check the permissions of a file, use ls -l . For more information on chmod, use man chmod.
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cd
Use cd to change directory. Use pwd to see what directory you are in.
% cd english
% pwd
% /u/ma/jeremy/english
% ls
novel poems
% cd novel
% pwd
% /u/ma/jeremy/english/novel
% ls
ch1 ch2 ch3 journal scrapbook
% cd ..
% pwd
% /u/ma/jeremy/english
% cd poems
% cd
% /u/ma/jeremy
Jeremy began in his home directory, then went to his english subdirectory. He listed this directory using ls , found that it contained two entries, both of which happen to be diretories. He cd’d to the diretory novel, and found that he had gotten only as far as chapter 3 in his writing. Then he used cd .. to jump back one level. If had wanted to jump back one level, then go to poems he could have said cd ../poems. Finally he used cd with no argument to jump back to his home directory.
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cp
Use cp to copy files or directories.
% cp foo foo.2
This makes a copy of the file foo.
% cp ~/poems/jabber .
This copies the file jabber in the directory poems to the current directory. The symbol “.” stands for the current directory. The symbol “~” stands for the home directory.
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date
Use this command to check the date and time.
% date
Fri Jan 6 08:52:42 MST 1995
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echo
The echo command echoes its arguments. Here are some examples:
% echo this
this
% echo $EDITOR
/usr/local/bin/emacs
% echo $PRINTER
b129lab1
Things like PRINTER are so-called environment variables. This one stores the name of the default printer — the one that print jobs will go to unless you take some action to change things. The dollar sign before an environment variable is needed to get the value in the variable. Try the following to verify this:
% echo PRINTER
PRINTER
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ftp
Use ftp to connect to a remote machine, then upload or download files. See also: ncftp
Example 1: We’ll connect to the machine
fubar.net, then change director to mystuff, then download the file homework11:
% ftp solitude
220
fubar.net FTP server (Version wu-2.4(11) Mon Apr 18 17:26:33 MDT 1994) ready.
Name (solitude:carlson): jeremy
331 Password required for jeremy.
Password:
230 User jeremy logged in.
ftp> cd mystuff
250 CWD command successful.
ftp> get homework11
ftp> quit
Example 2: We’ll connect to the machine
fubar.net, then change director to mystuff, then upload the file collected-letters:
% ftp solitude
220
fubar.net FTP server (Version wu-2.4(11) Mon Apr 18 17:26:33 MDT 1994) ready.
Name (solitude:carlson): jeremy
331 Password required for jeremy.
Password:
230 User jeremy logged in.
ftp> cd mystuff
250 CWD command successful.
ftp> put collected-letters
ftp> quit
The ftp program sends files in ascii (text) format unless you specify binary mode:
ftp> binary
ftp> put foo
ftp> ascii
ftp> get bar
The file foo was transferred in binary mode, the file bar was transferred in ascii mode.
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grep
Use this command to search for information in a file or files. For example, suppose that we have a file dict whose contents are
red rojo
green verde
blue azul
white blanco
black negro
Then we can look up items in our file like this;
% grep red dict
red rojo
% grep blanco dict
white blanco
% grep brown dict
%
Notice that no output was returned by grep brown. This is because “brown” is not in our dictionary file.
Grep can also be combined with other commands. For example, if one had a file of phone numbers named “ph”, one entry per line, then the following command would give an alphabetical list of all persons whose name contains the string “Fred”.
% grep Fred ph | sort
Alpha, Fred: 333-6565
Beta, Freddie: 656-0099
Frederickson, Molly: 444-0981
Gamma, Fred-George: 111-7676
Zeta, Frederick: 431-0987
The symbol “|” is called “pipe.” It pipes the output of the grep command into the input of the sort command.
For more information on grep, consult
% man grep
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head
Use this command to look at the head of a file. For example,
% head essay.001
displays the first 10 lines of the file essay.001 To see a specific number of lines, do this:
% head -n 20 essay.001
This displays the first 20 lines of the file.
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ls
Use ls to see what files you have. Your files are kept in something called a directory.
% ls
foo letter2
foobar letter3
letter1 maple-assignment1
%
Note that you have six files. There are some useful variants of the ls command:
% ls l*
letter1 letter2 letter3
%
Note what happened: all the files whose name begins with “l” are listed. The asterisk (*) is the ” wildcard” character. It matches any string.
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lpr
This is the standard Unix command for printing a file. It stands for the ancient “line printer.” See
% man lpr
for information on how it works. See print for information on our local intelligent print command.
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mkdir
Use this command to create a directory.
% mkdir essays
To get “into” this directory, do
% cd essays
To see what files are in essays, do this:
% ls
There shouldn’t be any files there yet, since you just made it. To create files, see cat or emacs.
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more
More is a command used to read text files. For example, we could do this:
% more poems
The effect of this to let you read the file “poems “. It probably will not fit in one screen, so you need to know how to “turn pages”. Here are the basic commands:
q — quit more
spacebar — read next page
return key — read next line
b — go back one page
For still more information, use the command man more.
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mv
Use this command to change the name of file and directories.
% mv foo foobar
The file that was named foo is now named foobar
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ncftp
Use ncftp for anonymous ftp — that means you don’t have to have a password.
> get jokes.txt
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print
This is a moderately intelligent print command.
% print foo
% print manuscript.dvi
In each case print does the right thing, regardless of whether the file is a text file (like foo ), a postcript file (like
notes.ps, or a dvi file (like manuscript.dvi. In these examples the file is printed on the default printer. To see what this is, do
% print
and read the message displayed. To print on a specific printer, do this:
% print foo jwb321
% print manuscript.dvi jwb321
To change the default printer, do this:
% setenv PRINTER jwb321
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pwd
Use this command to find out what directory you are working in.
% pwd
/u/ma/jeremy
% cd homework
% pwd
/u/ma/jeremy/homework
% ls
assign-1 assign-2 assign-3
% cd
% pwd
/u/ma/jeremy
%
Jeremy began by working in his “home” directory. Then he cd ‘d into his homework subdirectory. Cd means ” change directory”. He used pwd to check to make sure he was in the right place, then used ls to see if all his homework files were there. (They were). Then he cd’d back to his home directory.
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rm
Use rm to remove files from your directory.
% rm foo
remove foo? y
% rm letter*
remove letter1? y
remove letter2? y
remove letter3? n
%
The first command removed a single file. The second command was intended to remove all files beginning with the string “letter.” However, our user (Jeremy?) decided not to remove letter3.
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rmdir
Use this command to remove a directory. For example, to remove a directory called “essays”, do this:
% rmdir essays
A directory must be empty before it can be removed. To empty a directory, use rm.
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rsh
Use this command if you want to work on a computer different from the one you are currently working on. One reason to do this is that the remote machine might be faster. For example, the command
% rsh solitude
connects you to the machine solitude. This is one of our public workstations and is fairly fast.
See also: telnet
setenv
% echo $PRINTER
labprinter
% setenv PRINTER myprinter
% echo $PRINTER
myprinter
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sort
Use this command to sort a file. For example, suppose we have a file dict with contents
red rojo
green verde
blue azul
white blanco
black negro
Then we can do this:
% sort dict
black negro
blue azul
green verde
red rojo
white blanco
Here the output of sort went to the screen. To store the output in file we do this:
% sort dict >dict.sorted
You can check the contents of the file dict.sorted using cat , more , or emacs .
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tail
Use this command to look at the tail of a file. For example,
% tail essay.001
displays the last 10 lines of the file essay.001 To see a specific number of lines, do this:
% tail -n 20 essay.001
This displays the last 20 lines of the file.
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tar
Use create compressed archives of directories and files, and also to extract directories and files from an archive. Example:
% tar -tvzf foo.tar.gz
displays the file names in the compressed archive foo.tar.gz while
% tar -xvzf foo.tar.gz
extracts the files.
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telnet
Use this command to log in to another machine from the machine you are currently working on. For example, to log in to the machine “solitude”, do this:
% telnet solitude
See also: rsh.
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wc
Use this command to count the number of characters, words, and lines in a file. Suppose, for example, that we have a file dict with contents
red rojo
green verde
blue azul
white blanco
black negro
Then we can do this
% wc dict
5 10 56 tmp
This shows that dict has 5 lines, 10 words, and 56 characters.
The word count command has several options, as illustrated below:
% wc -l dict
5 tmp
% wc -w dict
10 tmp
% wc -c dict
56 tmp
