For a more concise guide, check out Penn's Social
Science Computing UNIX HELP
The UNIX system is an operating system that
allows several users to access one computer from several different terminals.
The file system is hierarchied- its directories and files are distributed
like the root/branch system of a tree. A directory can contain both directories
and files, so that once a directory has been created one can
create, open, save, or delete files within it. Typically all files
and directories within a unix system are contained within one directory-
the Root directory. A generic diagram might look like this:
Directories and files can be referred to according to their relative position. For example, the Fruit directory is in the Meal directory, which in turn is in the Home directory. One can also say that the Fruit directory is one down of the Meal directory or the Meal directory is one up of the Fruit. The "path" of a file is its position within the file system. To reach a file this path must be followed. The first command that is needed is the present working directory command. This command lets the user know what the current directory is. To use this command type "pwd" and the current path is listed. For example, if one is in the Fruit directory and one types "pwd" one receives the message "% /meal/fruit". The root directory is not specified since it is always assumed to be in the path. The next command lets the user continue down the path.
To access lower directories us the change directory command, "cd" followed by path name. It is important to note that every step down the tree is represented by the forward slash (/). So for example, if one is in the Meal directory and wishes to access the Fruit, one would type "cd /Fruit" This would then place the user in the Fruit directory. One can move down more than than one directory at a time by simply adding to the path. So if one were in the root directory and wished to access the Fruit one would type "cd /Meal/Fruit"
Finally, to move up the tree one uses the "cd.." command. This moves the user up one step on the tree. So if one is in the Fruit directory and types "cd.." then the user is sent to the Meal directory.
This is an example of the prompt when one is trying to access a path to the fruit directory.
roman:jbrown 1 % cd Meal/Fruit
(a) (b) (c) (d) (e) (f)
(a) the terminal "host" being used.
(b) the current operating directory. At the moment, it is the home
directory, which is the log-in name of the user.
(c) number of commands that have been entered in this xterm session
(d) command prompt
NOTE - In some cases, the setup may appear more like this
this will not change any of the processes. (the tilda, (~),
refers to the home directory)
Creating Directories and Files
To create a directory, after prompt (%) or (>), mkdir (filename)
roman:jbrown 1 % mkdir Meal
this will create a directory called Meal
(note - UNIX is case-sensitive, so there is a difference between "meal" and "Meal" - the capitals create different files)
One can make sure that the file has been created using the list command "ls", which lists all directories and files within the current directory.
roman:jbrown 2 % ls Meal
To move to the directory Meal,
roman:jbrown 3 % cd Meal
roman:Meal 4 %
Now you are in the 'Meal' directory, where you can create more
files and subsequent (sub)directories
At the prompt, type emacs (filename)
roman:Meal 4 % emacs light.supper
-this will open an emacs window buffer called "light.supper"
in which you can create and edit documents. During a session,
<cntrl-s> to save,
<cntrl-x> <cntrl-c> to save and exit.
[A save prompt should appear, "y" and there may also be a prompt asking if a "newline" should be added - again, "yes"]
(If a file name has more than one word, they should be linked together.
For instance, with a period, "light.supper", or underscore, "light_supper".
If this is not done, and you try to create the file,
%emacs light supper
Two files, file "light" and file "supper" will be created.
Underscores and periods are fine, but generally avoid other symbols, (*, $, !, etc.) since a particular symbol may be a unix command function and have a unexpected, probably inconvenient, result.)
After exiting, return to prompt, and list (ls) -
roman:Meal 5 % ls light.supper
Further directories and files can be created - in this scenario, in
the "Meal" directory. "breakfast" and "lunch".
( command prompt '%' or '>' )
% mkdir dirname
-make directory- creates new directory called (directoryname)
% cd dirname
-change current working directory
-go to upper-level (parent) directory
-return to home directory
-lists the files and directory contents
% ls -l
-lists the files and directory contents, as well as their condition
2 jbrown 1512 Jan 29 14:44 Help
(a) (b) (c) (d) (e)
- (a) permissions , (indicates if it is a directory or file, who can read, run, and/or edit it,)
- (b) the owner of the file ,
- (c) the size of the file in bytes ,
- (d) the last date and time it was worked on,
- (e) and the name of the file .
% more filename
-display the contents of a file by screen without opening an emacs session - read only, cannot edit
% (command) &
the (&) returns a prompt while the command process run
% emacs whist &
- means open emacs editor buffer of file "whist" and provide another prompt , %.
% cp afile newfile
file called newfile created, which is identical to afile - (note, if there is an already existing file in the same directory with the "newfile" name, it will be replaced )
% cp afile otherdir
-a new copy named afile is created in the directory otherdir
% cp afile afile2 otherdir
-a copy of afile and afile2 are made in otherdir
% cp -r adir newdir
-a copy of the directory is placed in newdir. The -r flag signifies that all files within adir are also copied.
% cp -r* . / newdir
-copy all files in this directory and in it's subdirectories
% rmdir dirname
-remove directory- will not do so if the directory is not empty, so the subdirectories must be specified
% rm filename
% mv oldname newname
-renames file from oldname to newname
% mv oldfile dirname
-move file to another directory.
% cat file1 file2 > newfile
-combine two files, create file called newfile
These are some of the most useful commands for creating and maneuvering directories and files in unix.
Other Useful Commands
% lpr filename
% head filename
-shows the first few lines of file named
% tail filename
-shows the last few lines of file named
-command used to search through files for a particular word or wordstring in a specific file or files-
ie. searching for word "porch" in the file called "tomcat"
% grep "porch" tomcat
An old lady is rocking away
the last of her days on her front porch,
Just then the old woman's cat walks across the porch in
front of them
Two lines in the file are found which contain the seached-for word string in the file named tomcat.
The grep command has several options, including
% grep -n filename
(Precede each line by its line number in the file (first line is 1).
% grep -i
(Ignore upper/lower case distinction during comparisons.)
% grep -h
(Prevents the name of the file containing the matching line from being appended to that line. Used when searching multiple files.)
For further, more detailed descriptions of commands, one can query the "manual page", a document containing in-depth, somewhat cryptic explanations of all the unix commands. there is a manpage book icon on your screen, however to access from an xterm, enter
% man (command)
roman:jbrown 1 % man cd
The manpage delivers detail explanations of the commands asked about, and it may help clarify and further any questions and further applications and arrangements of specific commands. If the specific command cannot be remembered, use the command "apropos "
roman:jbrown 1 % apropos cd
This will return a list of all commands in the manpage that contain "cd" in the one line command explanation.
to change your password, type
you will be prompted for the old password, then for the new password
i) at least six characters
ii) contain at least one numeric or special character
ii) must be different from login name
iv) new passwords must differ from the old by at least three
To change the background and border colors of the icons and windows
If you want to change the color of your borders, look in your .twmrc file in your home directory
% emacs .twmrc
In the section beneath the line
# Color settings,
one can chage the color in quotes to one reflecting a more personal color preference.
After the color has been changed in the file, save the changes, then on the greybackground of your screen, middle mouse key to get the "Window Ops" menu. Drag down to highlight "source .twmrc" - the changes you made will now be evident.
Change the background color of your clock...
% emacs .xsession
xclock -update 1 -padding 1 -geometry 60x60+68+0 -bg "blue" &
for no colors at all, (ie white screen), delete the current color entry
xclock -update 1 -padding 1 -geometry 60x60+68+0 &
xterm -C -title "Console" -n "console" -geometry 85x30+0-0 &
Just for fun -
at the prompt, type