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
• more --- use to read files
• mkdir --- create directory
• mv --- for moving and renaming files
• ncftp --- especially good for downloading files via anonymous ftp.
• 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 rojo
green verde
blue azul
<control-D>
%

<control-D> stands for "hold the control key down, then type the letter 'd'". The symbol ">" tells the computer that what is typed is to be put into the file named 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 (append) 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 the two files, dict and tmp, into one new file called dict2 like this:

%  cat dict tmp > dict2
%

We could check the number of lines in the new file like this:

%  wc -l dict2
7
%

The command wc counts things --- the number of characters, words, and line in a file.

chmod

This command is used to change the permissions (or access mode) of a file or directory. Only the owner of a file or a priveleged user may change its mode. 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 an executable command.

To check the permissions of a file, use ls -l. For more information on chmod and file permissions, use man chmod.

cd

Use cd to change directory. Use pwd to see what directory you are in.

%  pwd
/u/ma/jeremy
%  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
%  pwd
/u/ma/jeremy
%

Our user above, 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 directory 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, then cd'd to poems. If had wanted to jump back one level, then go to poems with just one command, he could have said cd ../poems. Finally he used cd with no argument to jump back to his home directory.

Remember, cd with no argument always returns you to your home directory.

cp

Use cp to copy files or directories.

%  cp  foo  foo.2

This makes a copy of the source-file foo with the new (destination-file) name foo.2.

%  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 user's home directory.

Note: If the destination-file exists BEFORE you give a cp command, cp just overwrites (and destroys the contents of) it. It is a good idea to use the interactive -i option with cp; it checks with you before it overwrites a file.

date

Use this command to check the date and time.

%  date
Fri Feb  7 08:52:42 PST 2003

Using the -u option displays the time in Greenwich Mean Time.

%  date
Fri Feb  7 16:52:42 PST 2003

Note: This command also sets the current date and time if a numeric string is supplied, but only a priveleged user may do so.

echo

The echo command copies (echoes) its arguments to standard output (the screen). 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

Use the command printenv to display values that have been set for your environment variables.

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 directory to mystuff, then download the file homework11:

%  ftp fubar.net
Connected to fubar.net.
220 fubar.net FTP server (Version wu-2.4(11) 
Mon Apr 18 17:26:33 MDT 1994) ready.
Name (fubar.net:jeremy): jeremy
331 Password required for jeremy.
Password: (password entered) 
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 directory to mystuff, then upload the file collected-letters:

%  ftp fubar.net
Connected to fubar.net.
220 fubar.net FTP server (Version wu-2.4(11) 
Mon Apr 18 17:26:33 MDT 1994) ready.
Name (fubar.net:jeremy): jeremy
331 Password required for jeremy.
Password: (password entered) 
230 User jeremy logged in.
ftp> cd mystuff
250 CWD command successful.
ftp> put collected-lettersquit

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 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 (think of it as "sends") the output of the grep command into the input of the sort command.

For more information on grep, use the command man grep

head

Use this command to look at the head of a file. For example,

%  head essay.001

displays the first 10 lines (the default is 10) 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.

To see all variants of ls, use the command man ls. One of the most useful is ls -trl.

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 use your favorite text editor (like vi, emacs, or pico).

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.

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.fubar.net
Connected to ftp.fubar.net
> get jokes.txt

The file jokes.txt is downloaded from the machine ftp.fubar.net.

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.

rm

Use rm to remove files from your directory.

%  rm foo
%
%  rm letter*
%

The first command removed a single file. The second command removed all files beginning with the string "letter". Be careful when using this command, the file(s) are automatically removed with no prompt to the user for confirmation. Using the -i option will prompt for confirmation before deleting each file.

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 (no files, no sub-directories) 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 solitude

connects you to the machine solitude.

See also telnet

setenv

Assigns a value to an environment variable. By itself, with no arguments, displays the names and values of all environment variables.

%  echo $PRINTER
labprinter
%  setenv PRINTER myprinter
%  echo $PRINTER
myprinter

In the above example, the first echo shows the value of the environment variable PRINTER, the setenv command changes the value of PRINTER to myprinter, and the final echo shows the new value of PRINTER.

sort

Use this commmand 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 your favorite text editor (vi, pico, 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 (because of the t option in particular) in the compressed archive foo.tar.gz while

%  tar -xvzf foo.tar.gz

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

You'll have to have an account (i.e., a login and password) on the machine you try to log in to. 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 rojo
green verde
blue azul
white blanco
black negro

Then we can do this

%  wc dict
     5      10      56  dict

This shows that dict has 5 lines, 10 words, and 56 characters.

The word count command has a few options, as illustrated below:

wc -l --- prints the line count only
wc -w --- prints the word count only
wc -c --- prints the character count only