Unix Notes
(by C.A.
Bertulani, 23 February, 2001)
Date,
whoami, echo
- If we want the computer to tell us today's date:
> date
Fri Feb 23 11:25:27 EST 2001
> whoami
carlos
whoami displays
the login name of the current user.
> 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 23 11:35:52 EST 2001
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 23 11:44:19 EST 2001) 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 23 11:44:19 EST 2001) 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, 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
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.
print
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!