Unix Notes
(by C.A. Bertulani ,)
Date, whoami , echo
- If we want the computer to tell us today's date:
> date
Fri Feb 23 2001
- Who am I?
> whoami
carlos
whoami displays the login name of the current user.
- echo
> echo This is a test
This is a test.
echo does just that: it tells the computer to retype the string "This is a test".
Managing Files
Your home directory
Figuring out what our home directory is:
> cd
> pwd
/home/ carlos
> echo $HOME
/home/ carlos
The cd
command ( c
hange
d
irectory
)
used with no arguments takes us from wherever we might be to our home
directory. The pwd
( p
rint
w
orking
d
irectory
) tells in which directory we find ourselves for
the moment. In the case at hand it is
/home/ carlos
.
Don't be concerned for the moment about the
/home/
part. It is a path
,
but that is irrelevant for now. Note that echo $HOME
has exactly the
same effect as pwd
.
Creating short files
Now let us create a short file. For this we use the cat command. Follow the example below carefully:
> cat > dict
red: vermelho
yellow: amarelo
black: negro
white: branco
blue: azul
green: verde
<control-d>
>
By <control-d> we mean: hold the control key down; while it is down press "d". We have just used cat to create a short English- portuguese dictionary. This dictionary resides in the file dict . We told cat to put what we typed in dict using the "into" symbol, namely > . To tell cat that we were done typing we typed control-d ("d" for "done"). To check that the dictionary is really there and that it was correctly entered we do this:
> ls
dict
> cat dict
red: vermelho
yellow: amarelo
black: negro
white: branco
blue: azul
green: verde
>
The ls
command l
ist
s
the files in the current directory. For
the moment there is only one, namely
dict
. The
command cat
shows us what is in
dict
.
Printing files
> print dict
Printing dict2 (text) on jwb129lab1
>
Print is not a standard Unix command. For this see " lpr ". The print command will try to figure out what kind of file you are trying to print and use the method it deems best. For more information on what it does, type the command with no arguments:
% print
... displays info on print ...
%
If you need a list of printers, use print -l . The "-l" is an option for the print command. Many Unix commands have options.
Note for those who need it: The print command understands dvi and postcript ( ps ) files. For example, print foo.dvi correctly prints foo.dvi , and print bar.ps correctly prints the postscript file bar.ps . If you need to force a file to be printed as text use print -t , e.g., print -t weirdfile .
Examining files
> wc
dict
6 12 78
> grep
white dict
white: branco
> sort dict
black: negro
blue: azul
green: verde
red: vermelho
white: branco
yellow: amarelo
>
The wc command c ounts w ords (and more). In the case at hand it tells us that dict contains 6 lines, 12 words, and 78 characters ("letters "). The grep command looks for the word white in the file dict and displays the lines in which this word appears. It gives us a way to search through files. The sort command does just what it says.
Saving a copy of our sorted dictionary: We'll put in a file called dict2 .
> sort dict
>dict2
> ls
dict
dict2
> cat dict2
black: negro
blue: azul
green: verde
red: vermelho
white: branco
yellow: amarelo
>
Notice once again the use of the "into"
symbol ">". In our example it had the effect of directing the
output of the sort command from the screen to the file
dict2
.
Just to be sure that everything went according to plan, we used ls
to be sure that
dict2
was there, and
we used cat dict2
to be sure that it contained what we thought it
should.
Getting rid of files
Use the rm command (for r e m ove ):
> ls
dict
dict2
> rm
dict2
rm
: remove dict2? y
> ls
dict
>
Creating and using directories
A directory is like a file folder which contains related documents (your files). As an example, suppose that when you list your files you see this:
> ls
fred1 fred2 fred3 ch1 ch2 ch3 foo.c
bar.c
>
The files fred1, etc. are letters to fred , the files ch1, etc. chapters of a book, and foo.c , bar.c are C programs.
The mdkir command.
We create a new directory using the mkdir command ( m ake d irectory ).
> mkdir
letters
> ls
fred1 fred2 fred3 ch1 ch2 ch3 foo.c
bar.c
letters
Notice that the directory letters shows up in the listing. If you are not sure what is a file and what is a directory, try this:
> ls
-F
fred1 fred2 fred3 ch1 ch2 ch3 foo.c
bar.c
letters/
Notice that
letters
is displayed
somewhat differently.
The mv command
Now we move the letters into the directory letters using the mv command ( m o v e).
> mv fred1 fred2 fred3 letters
> ls
ch1 ch2 ch3 foo.c
bar.c
letters
If we want to check that letters really contains the files it should, we do this:
> ls
letters
fred1 fred2 fred3
There is, by the way, a useful shortcut:
> mv
fred
* letters
Here the character * matches any sequence of characters, including the null string. Thus files named fred , fred101 , and freddy would all be moved into letters .
Paths
You can deal directly with files in a directory like this:
> cat letters/fred1
This command displays the contents of the file fred1 , which is in the directory letters . Here are some other ways of doing the same thing:
> cat letters/fred1
> more letters/fred1
> emacs
letters/fred1
We could even do this:
> cat l*f*1
Changing directories with cd
Sometimes it is better to work inside the directory letters . To do it we use the cd command ( ch hange d irectory ).
> cd letters
> ls
fred1 fred2 fred3
To go back to our home directory we do this:
> cd
To check that our home directory contains what it should.
> ls
ch1 ch2 ch3 foo.c
bar.c
letters
Now we make directories for the other files and move them into the right places:
> mkdir
book; mv
ch
* book
> mkdir
cprogs
; mv
*.c cprogs
> ls
-F
book/ cprogs
/ letters/
> ls
book
ch1 ch2 ch3
>
Where are we?
Sometimes in moving from one directory to another we lose track of where we are. To find out what the current directory is, use the pwd command ( p rint w orking d irectory ).
> pwd
carlos
> cd
book
> pwd
carlos
/book
>
Removing directories
To remove a directory we first remove all files in it, then remove the directory with rmdir ( r emove d irectory ).
> pwd
carlos
> cd
letters
% pwd
carlos
/letters
> rm
*
> cd
..
> rmdir
letters
The command rm * removes all files in the current directory. The command cd .. changes the current directory to the parent of the current one. In this case, it changes us from carlos /letters to carlos . Remember that carlos /letters is a path , as is carlos/letters/fred1 . The latter is the path which starts with Carlos's home directory and ends with the file fred1 .
Unix Command Summary
For more documentation on a command, consult a good book, or use the man pages. For example, for more information on grep , use the command man grep .
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
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 vermelho
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 vermelho
green verde
blue azul
>
If we wish to add text to an existing file we do this:
> cat >> dict
white branco
black negro
<control-D>
>
Now suppose that we have another file tmp that looks like this:
> cat tmp
cat gato
dog cachorro
>
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
12
The command wc counts things --- the number of characters, words, and line in a file.
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 .
cd
Use cd to change directory. Use pwd to see what directory you are in.
> cd english
> pwd
> /home/ carlos/english
> ls
novel poems
> cd novel
> pwd
> /home/ carlos/english/novel
> ls
ch1 ch2 ch3 journal scrapbook
> cd ..
> pwd
> /home/ carlos/english
> cd poems
> cd
> /home/ carlos
Carlos 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.
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.
date
Use this command to check the date and time.
> date
Fri Feb 232001
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
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 imagination.net , then change director to mystuff , then download the file homework11 :
> ftp quark
Connected to fubar.net.
220 imagination.net FTP server (Version wu-2.4(11) Fri Feb 232001) ready.
Name ( imagination:carlos ): carlos
331 Password required for carlos .
Password:
230 User carlos logged in.
ftp> cd mystuff
250 CWD command successful.
ftp> get homework11
ftp> quit
Example 2: We'll connect to the machine imagination.net , then change director to mystuff , then upload the file collected-letters :
> ftp magination
Connected to imagination.net.
220 fubar.net FTP server (Version wu-2.4(11) Fri Feb 232001) ready.
Name ( solitude:carlos ): carlos
331 Password required for carlos .
Password:
230 User carlos 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.
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 vermelho
green verde
blue azul
white branco
black negro
Then we can look up items in our file like this;
> grep red dict
red verrmelho
> grep branco dict
white branco
> 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,: 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
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 -20 essay.001
This displays the first 20 lines of the file.
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.
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.
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 .
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 .
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
ncftp
Use ncftp for anonymous ftp --- that means you don't have to have a password.
> ncftp ftp.imagination.net
Connected to ftp.imagination.net
> get jokes.txt
The file jokes.txt is downloaded from the machine ftp.imagination.net .
This is a moderately intelligent print command.
> print foo
> print notes.ps
> 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 notes.ps jwb321
> print manuscript.dvi jwb321
To change the default printer, do this:
> setenv PRINTER jwb321
pwd
Use this command to find out what directory you are working in.
> pwd
/home/ carlos
> cd homework
> pwd
/ carlos /homework
> ls
assign-1 assign-2 assign-3
> cd
> pwd
/home/ carlos
>
Carlos 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.
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 (Carlos?) decided not to remove letter3.
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.
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 quark
connects you to the machine quark .
See also: telnet
setenv
> echo $PRINTER
labprinter
> setenv PRINTER myprinter
> echo $PRINTER
myprinter
sort
Use this commmand to sort a file. For example, suppose we have a file dict with contents
red vermelho
green verde
blue azul
white branco
black negro
Then we can do this:
> sort dict
black negro
blue azul
green verde
red vermelho
white branco
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 .
tail
Use this command to look at the tail of a file. For example,
> head essay.001
displays the last 10 lines of the file essay.001 To see a specific number of lines, do this:
> head -20 essay.001
This displays the last 20 lines of the file.
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.
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 "imagination", do this:
> telnet imagination
See also: rsh .
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 vermelho
green verde
blue azul
white branco
black negro
Then we can do this
> wc dict
5 10 60 tmp
This shows that dict has 5 lines, 10 words, and 60 characters.
The word count command has several options, as illustrated below:
> wc -l dict
5 tmp
> wc -w dict
10 tmp
> wc -c dict
60 tmp
Good luck!