A Small UNIX Tutorial

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A Small UNIX Tutorial

• By CGS3063 staff

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Whats UNIX?

• An operating system claimed to be standard
  from microcomputers to supercomputers
• Invented by ATT Bell Labs in late 60s
• Currently there are different versions of UNIX
  such as SunOS, Linux, DEC OSF/1, AIX, HP-UX 10,
  Solaris, IRIX, SCO UNIX, etc.

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Why we need UNIX?

• For this class you need to work from your class
  grove account to finish your homework and/or
  submit your term paper
• Knowing basic UNIX commands is essential to
  finish your homework

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UNIX Commands

• ls names list files contained in a directory
  name or that match a file name. If no name is
  given list those files in current directory.
• ls a list all files including hidden files
• ls l list in long format (including details
  like permissions, owner, size, etc.), works very
  much like dir
• ls al list all files (including hidden files)
  in long format
• ls dl dir_name lists information about the
  directory, dir_name.

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What is a Directory?

• Your home directory might contain a public_html
  directory. Your public_html directory might
  contain an index.html file.

c3063xxx
public_html
index.html
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What is a Directory?

• A file cannot hold a directory or a file!

c3063xxx
public_html
index.html
New_file_or_directory
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What is directory?

• Directories can hold files and other directories

/
tmp
users
bin
etc
backup
usern
file1
user2

public_html
user1
index.html
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Whats a directory?

• Files are grouped in the directory structure.
  The file-system is arranged like hierarchical
  tree (inverted)structure.
• The top of the tree is called root which
  usually contains several sub-directories. In UNIX
  /(forward slash) is used to present the root.
  

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Pathnames

• Absolute Pathnames
• In the previous tree /users/usern/file1 is an
  absolute pathname.

• Relative pathnames
• If you are already in the users directory, the
  relative pathname for file1 is usern/file1.

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Specifying Paths

• What is the absolute path to index.html?

/
tmp
users
bin
etc
backup
usern
file1
user2

public_html
user1
index.html
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Specifying Paths

• What is the relative path to index.html (assuming
  that usern is your pwd)?

/
tmp
users
bin
etc
backup
usern
file1
user2

public_html
user1
index.html
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More UNIX commands

• pwd let you know the absolute pathname of your
  current working directory (Print Working
  Directory)
• cd dir change directory
• cd .. go back to parent directory. .. is the
  relative pathname to the parent directory.
• . -stands for current (working) directory.
• the tilde character can refer your home
  directory

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More UNIX commands

• mkdir directories create one or more
  directories. You can specify them by absolute or
  relative pathnames.
• cp
• cp file1 file2 copy file1 to file2. If theres
  already a file2, the old one will be overwritten.
• cp file(s) directory file(s) will be copied to
  the directory.

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More UNIX commands

• mv sourcefile targetfile basically mv renames
  sourcefile to targetfile. If theres a file with
  the same name as targetfile, it will be
  overwritten. mv works for directories in a
  similar fashion.

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More UNIX commands

• rm file(s) delete file(s).
• rmdir directories delete one or more empty
  directories.
• rm r directories can be used to delete non
  empty directories. !!!WARNING!!! This will DELETE
  EVERYTHING in that directory!!!
• You can not recover your files after you removed
  them (unlike Windows OS).

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Permissions

• There are three types of file access supported by
  UNIX.
• r read, view the contents of a file or a
  directory
• w write, edit file/directory contents
• x execute, run executable file

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Permissions

• Heres an example
• Suppose you type in ls -l and the result is
• rwx r-x r-- 1 hans doc 858 Aug 22 2228 hw1
• What do all these symbols mean?

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Permissions

• - rwx r-x r-- 1 hans doc 858 Aug 22 2228 hw1

owner
links
type
File name
size
Modification date/time
group
User permissions
Group permissions
Other Permissions
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Permissions

• User the person who created the file.
• Group the group owns the file.
• Other the rest of the world
• 754 is a decimal number. But you can represent
  each digit with a binary number.
• 4 gt read permission, 2 gt write permission,
• 1gt execute permission

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Permissions

• read4write 2execute1
• rwx r-x r--

4 2 1
4 0 1
4 0 0
7 5 4
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Permissions

• rwx r-x r-- is a symbolic way to specify file
  modes, while 754 is a numeric way (remember 7 ?
  111, 5 ?101, 4?100 ? ). How would you represent
  this file mode numerically?
• --x --x wx
• How would you represent this bit string
  symbolically?
• 6 1 4

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Permissions

• chmod mode file(s) another UNIX command! Change
  the access mode of one or more files. Examples
• chmod 751 my_file the owner of my_file has
  rwx(7) permission, the group has r-x(5)
  permission, others have --x permission.
• Tell me what the following command will do?
• chmod urwx, gr, owr my_file
• Remember user, group and others?

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Get started

• Create a new directory in your grove account
  named public_html by using the following command,
• mkdir public_html
• Go to this directory
• cd public_html
• Use pico to create a new file named index.html

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Editor in UNIX

• Some short cuts for the pico editor
• G Get Help
• O WriteOut
• R Read File
• Y Prev Pg
• K Cut Text
• C Cur Pos
• X Exit
• J Justify
• W Where is
• V Next Pg
• U UnCut Text
• T To Spell

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Get started

• After you save the file index.html, change the
  mode of this file by using the following command,
  
• chmod 644 index.html
• (urw-, gr--, or--)
• Check whether you did it right
• ls l or dir
• (What result should be displayed?)

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Get started

• Then go back to parent directory
• cd ..
• Change the mode of public_html directory
• chmod 755 public_html
• ( Whats the meaning of this command?)
• Check if you got the mode set right
• ls dl public_html

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Where to get help?

• Come to see us during the office hours
• The CGS3063 tutorial available on line (technical
  info)
• man subject(s) the UNIX help command.
• e.g. to get help info about mv command you can
  type man mv to get detailed manual of mv command.

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Thank you and good luck!