Sunday, June 29, 2008

Unix Basics

Basic UNIX commands
Note: not all of these are actually part of UNIX itself, and you may not find them on all UNIX machines. But they can all be used on turing in essentially the same way, by typing the command and hitting return. Note that some of these commands are different on non-Solaris machines - see SunOS differences.
If you've made a typo, the easiest thing to do is hit CTRL-u to cancel the whole line. But you can also edit the command line (see the guide to More UNIX).
UNIX is case-sensitive.
Files
• ls --- lists your files
ls -l --- lists your files in 'long format', which contains lots of useful information, e.g. the exact size of the file, who owns the file and who has the right to look at it, and when it was last modified.
ls -a --- lists all files, including the ones whose filenames begin in a dot, which you do not always want to see.
There are many more options, for example to list files by size, by date, recursively etc.
• more filename --- shows the first part of a file, just as much as will fit on one screen. Just hit the space bar to see more or q to quit. You can use /pattern to search for a pattern.
• emacs filename --- is an editor that lets you create and edit a file. See the emacs page.
• mv filename1 filename2 --- moves a file (i.e. gives it a different name, or moves it into a different directory (see below)
• cp filename1 filename2 --- copies a file
• rm filename --- removes a file. It is wise to use the option rm -i, which will ask you for confirmation before actually deleting anything. You can make this your default by making an alias in your .cshrc file.
• diff filename1 filename2 --- compares files, and shows where they differ
• wc filename --- tells you how many lines, words, and characters there are in a file
• chmod options filename --- lets you change the read, write, and execute permissions on your files. The default is that only you can look at them and change them, but you may sometimes want to change these permissions. For example, chmod o+r filename will make the file readable for everyone, and chmod o-r filename will make it unreadable for others again. Note that for someone to be able to actually look at the file the directories it is in need to be at least executable. See help protection for more details.
• File Compression
o gzip filename --- compresses files, so that they take up much less space. Usually text files compress to about half their original size, but it depends very much on the size of the file and the nature of the contents. There are other tools for this purpose, too (e.g. compress), but gzip usually gives the highest compression rate. Gzip produces files with the ending '.gz' appended to the original filename.
o gunzip filename --- uncompresses files compressed by gzip.
o gzcat filename --- lets you look at a gzipped file without actually having to gunzip it (same as gunzip -c). You can even print it directly, using gzcat filename | lpr
• printing
o lpr filename --- print. Use the -P option to specify the printer name if you want to use a printer other than your default printer. For example, if you want to print double-sided, use 'lpr -Pvalkyr-d', or if you're at CSLI, you may want to use 'lpr -Pcord115-d'. See 'help printers' for more information about printers and their locations.
o lpq --- check out the printer queue, e.g. to get the number needed for removal, or to see how many other files will be printed before yours will come out
o lprm jobnumber --- remove something from the printer queue. You can find the job number by using lpq. Theoretically you also have to specify a printer name, but this isn't necessary as long as you use your default printer in the department.
o genscript --- converts plain text files into postscript for printing, and gives you some options for formatting. Consider making an alias like alias ecop 'genscript -2 -r \!* | lpr -h -Pvalkyr' to print two pages on one piece of paper.
o dvips filename --- print .dvi files (i.e. files produced by LaTeX). You can use dviselect to print only selected pages. See the LaTeX page for more information about how to save paper when printing drafts.
Directories
Directories, like folders on a Macintosh, are used to group files together in a hierarchical structure.
• mkdir dirname --- make a new directory
• cd dirname --- change directory. You basically 'go' to another directory, and you will see the files in that directory when you do 'ls'. You always start out in your 'home directory', and you can get back there by typing 'cd' without arguments. 'cd ..' will get you one level up from your current position. You don't have to walk along step by step - you can make big leaps or avoid walking around by specifying pathnames.
• pwd --- tells you where you currently are.
Finding things
• ff --- find files anywhere on the system. This can be extremely useful if you've forgotten in which directory you put a file, but do remember the name. In fact, if you use ff -p you don't even need the full name, just the beginning. This can also be useful for finding other things on the system, e.g. documentation.
• grep string filename(s) --- looks for the string in the files. This can be useful a lot of purposes, e.g. finding the right file among many, figuring out which is the right version of something, and even doing serious corpus work. grep comes in several varieties (grep, egrep, and fgrep) and has a lot of very flexible options. Check out the man pages if this sounds good to you.
About other people
• w --- tells you who's logged in, and what they're doing. Especially useful: the 'idle' part. This allows you to see whether they're actually sitting there typing away at their keyboards right at the moment.
• who --- tells you who's logged on, and where they're coming from. Useful if you're looking for someone who's actually physically in the same building as you, or in some other particular location.
• finger username --- gives you lots of information about that user, e.g. when they last read their mail and whether they're logged in. Often people put other practical information, such as phone numbers and addresses, in a file called .plan. This information is also displayed by 'finger'.
• last -1 username --- tells you when the user last logged on and off and from where. Without any options, last will give you a list of everyone's logins.
• talk username --- lets you have a (typed) conversation with another user
• write username --- lets you exchange one-line messages with another user
• elm --- lets you send e-mail messages to people around the world (and, of course, read them). It's not the only mailer you can use, but the one we recommend. See the elm page, and find out about the departmental mailing lists (which you can also find in /user/linguistics/helpfile).
About your (electronic) self
• whoami --- returns your username. Sounds useless, but isn't. You may need to find out who it is who forgot to log out somewhere, and make sure *you* have logged out.
• finger & .plan files
of course you can finger yourself, too. That can be useful e.g. as a quick check whether you got new mail. Try to create a useful .plan file soon. Look at other people's .plan files for ideas. The file needs to be readable for everyone in order to be visible through 'finger'. Do 'chmod a+r .plan' if necessary. You should realize that this information is accessible from anywhere in the world, not just to other people on turing.
• passwd --- lets you change your password, which you should do regularly (at least once a year). See the LRB guide and/or look at help password.
• ps -u yourusername --- lists your processes. Contains lots of information about them, including the process ID, which you need if you have to kill a process. Normally, when you have been kicked out of a dialin session or have otherwise managed to get yourself disconnected abruptly, this list will contain the processes you need to kill. Those may include the shell (tcsh or whatever you're using), and anything you were running, for example emacs or elm. Be careful not to kill your current shell - the one with the number closer to the one of the ps command you're currently running. But if it happens, don't panic. Just try again :) If you're using an X-display you may have to kill some X processes before you can start them again. These will show only when you use ps -efl, because they're root processes.
• kill PID --- kills (ends) the processes with the ID you gave. This works only for your own processes, of course. Get the ID by using ps. If the process doesn't 'die' properly, use the option -9. But attempt without that option first, because it doesn't give the process a chance to finish possibly important business before dying. You may need to kill processes for example if your modem connection was interrupted and you didn't get logged out properly, which sometimes happens.
• quota -v --- show what your disk quota is (i.e. how much space you have to store files), how much you're actually using, and in case you've exceeded your quota (which you'll be given an automatic warning about by the system) how much time you have left to sort them out (by deleting or gzipping some, or moving them to your own computer).
• du filename --- shows the disk usage of the files and directories in filename (without argument the current directory is used). du -s gives only a total.
• last yourusername --- lists your last logins. Can be a useful memory aid for when you were where, how long you've been working for, and keeping track of your phonebill if you're making a non-local phonecall for dialling in.
Connecting to the outside world
• nn --- allows you to read news. It will first let you read the news local to turing, and then the remote news. If you want to read only the local or remote news, you can use nnl or nnr, respectively. To learn more about nn type nn, then \tty{:man}, then \tty{=.*}, then \tty{Z}, then hit the space bar to step through the manual. Or look at the man page. Or check out the hypertext nn FAQ - probably the easiest and most fun way to go.
• rlogin hostname --- lets you connect to a remote host
• telnet hostname --- also lets you connect to a remote host. Use rlogin whenever possible.
• ftp hostname --- lets you download files from a remote host which is set up as an ftp-server. This is a common method for exchanging academic papers and drafts. If you need to make a paper of yours available in this way, you can (temporarily) put a copy in /user/ftp/pub/TMP. For more permanent solutions, ask Emma. The most important commands within ftp are get for getting files from the remote machine, and put for putting them there (mget and mput let you specify more than one file at once). Sounds straightforward, but be sure not to confuse the two, especially when your physical location doesn't correspond to the direction of the ftp connection you're making. ftp just overwrites files with the same filename. If you're transferring anything other than ASCII text, use binary mode.
• lynx --- lets you browse the web from an ordinary terminal. Of course you can see only the text, not the pictures. You can type any URL as an argument to the G command. When you're doing this from any Stanford host you can leave out the .stanford.edu part of the URL when connecting to Stanford URLs. Type H at any time to learn more about lynx, and Q to exit.
Miscellaneous tools
• webster word --- looks up the word in an electronic version of Webster's dictionary and returns the definition(s)
• date --- shows the current date and time.
• cal --- shows a calendar of the current month. Use e.g., 'cal 10 1995' to get that for October 95, or 'cal 1995' to get the whole year.
password
When you received your username and password from the consulting desk, the password was a generated password. You should personalize your own password so that it is easy to remember without being something others could easily guess. It should not be a word that is in a dictionary (as a program can be written to try all the words in a dictionary in seconds). Your password has to be at least 6 characters. It can be letters (UPPER case or lower case) or numbers. CHANGE IT!
DO NOT give your password to others. This is an account and you are responsible for what is done on this account. If you give the password to someone else and they do something wrong, your account information will be pointing to you. DO NOT give your password to others.
If or when you change your password, it might take a few minutes for the new password to be activated. There are several changes that must take place on several computers. Be patient. If you just changed your password and the new password doesn't work yet, the old password is still active and it will work.
type this in this is what it will do
sunburst% password you will be prompted to enter your old password
old password enter your old password here
new password you will be asked to enter a new password
new password type it again for verification
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ls (list schema)
The ls command displays the files and directories in your current working directory. If there are no visible files in your directory, the UNIX prompt will be returned. ls does not display hidden files which begin with a . (period). To display all files you must include the option -a.
type this in this is what it will do
sunburst% ls displays the files and directories in your current directory
sunburst% ls -a displays all files and directories (even the hidden ones)
sunburst% ls -l displays all files and directories w/FULL description
sunburst% dir same as ls -l (alias for DOS people)
sunburst% ls -R displays all files and directories in current directory and below (recursive)
You should not delete or change any hidden files. These files are created for administrative use of your e-mail, news readers, login, etc.
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mkdir (make directory)
The mkdir command will create a subdirectory inside of your current working directory. If you are logged into sunburst go ahead and try the command as follows.
type this in this is what will happen
sunburst% mkdir tutor_stuff this will create a subdirectory called tutor_stuff
Now let us look to make sure the directory was actually created.
sunburst% ls should display your files and subdirectories in your current working directory (including the subdirectory you just created.)
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cd (change directories)
The cd command will change the current working directory to the location or path you type.
sunburst% cd tutor_stuff change the working directory to tutor_stuff
sunburst% cd .. cd followed by .. will take you to the current parent directory
sunburst% cd cd by itself will take you to your home directory
no matter where you currently are
sunburst% cd tutor_stuff change the working directory to tutor_stuff
If you type in the ls command here (make sure you are inside of tutor_stuff) you should see that the directory (you just created) is empty. Try it and see! Now that you are in the directory called tutor_stuff create another subdirectory called more_stuff. We will use this subdirectory later.
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touch (touches a file and updates it)
The touch command will update the last time a file was edited. If you touch a file that doesn't yet exist, it will create a file with zero length. You probably won't use it much, but it will allow us to easily create files that we will use and delete later.
sunburst% cd ~/tutor_stuff makes sure everyone is in the right place
sunburst% touch testfile creates a file named testfile
sunburst% ls check to see if the file is there
Create another file of your own choice. Make sure you remember the name so you can delete it later.
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pwd (print working directory)
The pwd command shows you where you are (path wise) on the computer (server - not your desktop). You have probably noticed that every time you change directories you get a description of the path. Sometimes it is necessary to know your current path without changing to a different directory.
sunburst% cd takes you to your home directory
sunburst% pwd prints your working directory
you should see something like /home/coyote/username
sunburst% cd tutor_stuff takes you to tutor_stuff subdirectory
sunburst% pwd you should see /home/coyote/username/tutor_stuff
See if you can get back to the more_stuff subdirectory. Next, have the full pathname printed to the screen using the pwd command. (Can you guess what the full pathname will be?)
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Miscellaneous stuff about directories and pathnames
Follow the directions and make sure you understand what is happening.
sunburst% cd takes you to your home directory
sunburst% ls lists files and directories in the current directory
sunburst% ls tutor_stuff lists files and directories inside of tutor_stuff
sunburst% ls what is not a directory and will say "what not found"
sunburst% ls ~ lists files and directories in your home directory
(no matter where you currently are in the system)
The tilde (~) is a reference to your home directory.
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cp (copy file)
You can make an exact copy of a file using the copy (cp) command.
sunburst% cd ~/tutor_stuff makes sure everyone is in the right place
sunburst% cp testfile file2 makes a copy of testfile and calls it file2
sunburst% dir make sure the files are really there
See if you can make a copy of file2 (call it file3).
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mv (move file)
The mv command moves files and directories around in the file system. You can also use the mv command to rename a file. To make sure these examples work you must be inside of tutor_stuff with the testfile and file2 created.
sunburst% mv testfile file1 renames testfile with the name of file1
sunburst% mv file1 .. moves file1 to its parent directory
sunburst% mv file2 more_stuff moves file2 into subdirectory more_stuff
See if you can move the file2 that is in more_stuff back to tutor_stuff. Also move the file1 that is in home directory back to tutor_stuff. If you do this you should have file1, file2, and file3 inside of tutor_stuff. Use the dir or ls commands to make sure you moved the files to the right spots.
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rm (remove file)
The rm command removes or deletes files from the file system. You must be careful. DO NOT delete anything you might need later. You can't get it back.
sunburst% rm file1 removes file1
sunburst% rm file3 .. removes file3
Check to see that file2 still exists and that file1 and file3 are gone. Then remove file2.
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rmdir (remove directory)
The rmdir command will remove an empty directory. If you have followed closely up to this point you should not have any files in the subdirectory more_stuff, so let's remove that directory.
sunburst% cd ~/tutor_stuff makes sure everyone is in the right place
sunburst% rmdir more_stuff removes directory called more_stuff
See if you can remove the directory tutor_stuff. You need to make sure that there are no files or directories inside. (Remember you created another file of your choice - with a touch command earlier.)
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chmod (changing a file mode)
The chmod command lets the owner of a file change the permissions settings for a file or directory. These permissions are displayed with the dir or ls -l listings. The permissions are in the form of
-rwxrwxrwx
This collection of letters tells us how the permissions for a file (starting with a -) or directory (starting with a d) are set. The first three letters give the permissions for the owner of the file. The middle group (next three letters) give us the permissions for the group to which the owner belongs. The last three letters tell the permissions for everyone else. The permissions can be set for directories as well as files but have slightly different meanings.
files
• r- read permission
• w-write permission
• x-execute permission
directories
• r-permission to list files in a directory
• w-permission to delete files or move files
• x-permission to access to files in the directory
permissions
owner group everyone
- rwx rwx rwx
codes r - Read Permission
4
w- Write Permission 2
x- Execute Permission


If you wanted to set a file with full permissions for yourself or owner (4+2+1)=7, read and write permissions for the group (4+2)=6 and read only for everyone 4=4, the command would be
chmod 764 filename.
Depending on what you are doing with (and from) the files, the permissions need to be set appropriately for owner, group and everyone.
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du (disk utility)
The du command prints the number of kilobytes you have in each subdirectory. This can be useful to see which directory has the most files if you have gone over quota. From your home directory type
sunburst% du
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quota (displays user quota and usage)
Each user on sunburst is allocated a certain amount of disk space (usually about 5 megabytes). If you exceed this quota some of your files must be removed within a certain time period. To check your quota and see how much you are using type
sunburst% quota -v
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clear (clears screen)
The command clear just clears your terminal screen. Go ahead and try this. You should see a clear terminal window with sunburst% at the top.
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Ways to display file contents
In order for us to experiment with the next five commands, we need to create an example file. To do this you can either type the list below exactly as it appears or you can highlight (or select) the list below and cut-n-paste it into UNIX at the sunburst% prompt. Either way will work the same. In this example we are sending the input from the keyboard into the file demofile. AFTER the list is either typed into UNIX or pasted from Netscape into UNIX you must stop the input with a return and a control-d.
---------------------------list below
cat > demofile
one
two
three
four
five
six
seven
eight
nine
ten
eleven
twelve
thirteen
fourteen
fifteen
sixteen
seventeen
eighteen
nineteen
twenty
twenty-one
twenty-two
twenty-three
twenty-four
twenty-five
twenty-six
------------------list above
AFTER the list is either typed into UNIX or pasted from Netscape into UNIX you must stop the input with a return and a control-d.
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cat (concatenate)
The cat command will display the entire contents of the file on the terminal screen. If it is more than one page it will all scroll by quickly.
sunburst% cat demofile displays entire file contents to terminal screen
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more (display one screen at a time)
To display the entire file one screen at a time use the more command instead of cat. After each screen is drawn you must hit the space bar to go on to the next screen.
sunburst% more demofile displays the file example one screen at a time
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head (display first 10 lines of a file)
The head command will display the first 10 lines of a file.
sunburst% head demofile should display one - ten in our demofile
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tail (displays last 10 lines of a file)
displays last 10 lines of a file
sunburst% tail demofile should display seventeen-twenty-six in our file
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wc (word count)
The wc command will tell you how many lines, words and characters.
sunburst% wc demofile would return 26 lines 26 words and about 170 letters
If you pasted the info from Netscape there would be a few more letters because of additional spaces used in formatting HTML (approximately 383 letters).
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* (wild card - matches none or more )
The * is a wild card that will replace anything in its place. Below are some examples of its use.
sunburst% dir *.gif displays all files ending with .gif
sunburst% dir test* displays all files beginning with test
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? (wild card - matches just one character)
The ? is a wild card that will match one character only. Below is an examples of its use.
sunburst% dir test?.gif displays all files starting with test
then valid character
then ending with .gif
would not find test10.gif
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file name conventions
Unix file names should contain only letters, numbers, underscore and period (. often referred to as dot). The file names can contain up to 256 characters. Try to give your file names meaning. Don't use all 256 characters.
Directories are basically a special type of file, so the rules for naming files apply to directories also.
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!!
This is called the bang bang command. It will repeat the last command entered into unix from your keyboard. This is like the F3 command from DOS.
Try it!
A variation of this is ! followed by a letter (or letters). This will re-issue the last unix command that started with that letter (or letters). Lets look at the following example:
sunburst% dir would display the current working directory
sunburst% !! would repeat last command
sunburst% mkdir stuff creates directory stuff
sunburst% clear clears the terminal window
sunburst% cd stuff change working directory to stuff
sunburst% !c would try to change directories again
this wouldn't work because you are already there
sunburst% !cl would send the last unix command starting with cl which would be clear
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More help directly from UNIX here
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man
Read the UNIX on line manual page for a specific command.
sunburst% man cp displays online manual for copy command
Notice the --More--(26%) message at the bottom of the screen (if you type the above command). If you do not want to view the remaining pages you can [interrupt Process] with the Control-C command.
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whatis
The whatis command will display a one-line explanation of a command.
sunburst% whatis cp displays a one-line description of the cp command
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apropos
If you don't remember the UNIX command but you know you want to copy a file you can use the apropos command to find reference to the copy command within the online manual.
sunburst% apropos copy displays references to copy within the online manuals
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A little fun?
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finger
If you want to find out some information about another user (such as: are they logged on, when did they read their mail last, do they have a plan) you can use the finger command. The finger command reads some of those invisible files in your directory we were talking about earlier to display the information you will see on your screen.
sunburst% finger username@host displays information regarding the person you are checking on
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talk
If you fingered someone and know that they are currently logged into sunburst you can talk to them. The talk command will split your window into a upper portion and lower portion. You will type on one and read the person's responses an the other port ion. It is kind of like a telephone (well no sound). You can do this with anyone in the world that is logged on if you know their e-mail address.
After you issue the talk command the other person should see a message that says you are requesting to talk to them. If they want to talk to you they need to type in a corresponding message on their computer screen.

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