UNLV National Supercomputing Institute

NSI Home About Us Our Affiliates Resources Documentation Current Research Current Issues New Account Reset Password Request Help Contact Us

cat	for creating and displaying short files
chmod	change file 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
man	display man page for command
more	use to read files
mkdir	create directory
mv	for moving and renaming files
ncftp	especially good for downloading files via anonymous ftp.
passwd	change your login password
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
vi	vi (visual) editor
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 dictionary.

host% cat > dictionary red rojo green verde blue azul <control-D> host%

If we wish to add (append) text to an existing file we do this:

host% cat >> dictionary white blanco black negro <control-D> host%

Now suppose that we have another file tmp that looks like this:

host% cat tmp cat gato dog perro host%

Then we can join the two files, dictionary and tmp, into one new file called dictionary2 like this:

host% cat dictionary tmp > dictionary2 host%

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

host% wc -l dictionary2 7 host%

The command wc counts things --- the number of characters, words, and lines 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.

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

host% pwd /u/ma/jeremy host% cd english host% pwd /u/ma/jeremy/english host% ls novel poems host% cd novel host% pwd /u/ma/jeremy/english/novel host% ls ch1 ch2 ch3 journal scrapbook host% cd .. host% pwd /u/ma/jeremy/english host% cd poems host% cd host% pwd /u/ma/jeremy host%

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.

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.

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

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

host% date -u Fri Feb 7 16:52:42 UTC 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:

host% echo this this host% echo $EDITOR /usr/local/bin/emacs host% echo $PRINTER b129lab1

Things like PRINTER are 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:

host% echo PRINTER PRINTER

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

ftp

note: it is usually better to use either scp or sftp to copy files as these commands encrypt the communications to prevent eavesdropping on the passwords or transferred content.

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:

host% 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:

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 dictionary whose contents are

red rojo green verde blue azul white blanco black negro

Then we can look up items in our file like this

host% grep red dictionary red rojo host% grep blanco dictionary white blanco host% grep brown dictionary host%

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.

host% 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 a connector) 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,

host% 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:

host% 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.

host% ls foo letter2 foobar letter3 letter1 maple-assignment1 host%

Note that you have six files. There are some useful variants of the ls command:

host% ls l* letter1 letter2 letter3 host%

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.

host% mkdir essays

To get "into" this directory, do

host% cd essays

To see what files are in essays, do this:

host% ls

There shouldn't be any files there yet, since you just made it. To create files, see cat or use your favored text editor (like vi, emacs, or pico).

man

man is the command used to display unix manual pages. for example to display the manual page for the ls command:

cherry-creek$ man ls

If you do not know the command/library etc. that you want the manpage for use the -k option to display any manpages with keyword in the title.

More is a command used to read text files. For example, we could do this:

host% 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
spacebar	advance one screen
return key	advance one line
b	go back one screen

For still more information, use the command man more.

Use this command to change the name of file and directories.

host% 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.

host% ncftp ftp.fubar.net Connected to ftp.fubar.net > get jokes.txt

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

passwd

Use this command to change your account password.

host% passwd passwd: Changing password for jeremy Enter existing login password: New Password: Re-enter new Password: passwd: password successfully changed for jeremy host%

Jeremy typed his current password at the Enter existing login password: prompt, but the passwd command turns off the terminal echo so that what Jeremy types wont show up in the terminal history or be visible to someone looking on. After typing his new password at the New Password: prompt Jeremy is asked to re-enter the password to ensure he typed it correctly. Depending on the system a password change may fail due to insuficient complexity or password history.

pwd

Use this command to find out what directory you are working in.

host% pwd /u/ma/jeremy host% cd homework host% pwd /u/ma/jeremy/homework host% ls assign-1 assign-2 assign-3 host% cd host% pwd /u/ma/jeremy host%

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.

host% rm foo host% host% rm letter* host%

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:

host% 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

host% rsh solitude

connects you to the machine solitude.

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