Unix Command Summary

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Unix Command Summary

See the Unix tutorial for a leisurely, self-paced introduction on how to use the commands listed below. 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 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.

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.

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 directories. 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.

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 Jan 6 08:52:42 MST 1995

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 fubar.net, then change director to mystuff, then download the file homework11:

   % ftp solitude
     Connected to fubar.net.
     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:

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 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.

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 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.

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
/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.

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.

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 solitude

connects you to the machine solitude. This is one of our public workstations and is fairly fast.