UNIX Commands

Basic Unix Commands-----1

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 anonymousftp.

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 filedict. 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 onchmod, use man chmod.

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 diretorynovel, 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

Unix commands-2

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:

   % 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> 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 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.

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 lscommand:

   % 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.

Unix commands-3

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.fubar.net

     Connected to ftp.fubar.net

   > get jokes.txt

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

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.

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.

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 filedict 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 , oremacs .

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 "solitude", do this:

   % telnet solitude

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 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