CS 497C

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CS 497C Introduction to UNIXLecture 12 - The
File System

• Chin-Chih Changchang_at_cs.twsu.edu

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Relative Pathnames (. and ..)

• A relative pathname is a pathname which defines
  the location of a file with with respect to the
  current directory.
• It uses the symbols . (a single dot) and .. (two
  dots) to refer to the current and parent
  directories, respectively.
• The command cd .. change your directory to the
  parent directory of the current directory.

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Relative Pathnames (. and ..)

• pwd
• /home/remeo/progs
• cd ../..
• pwd
• /home
• For example, if you are in your home directory
  /home/romeo and you want to display the contents
  of /etc/service, you can use either one of
  following ways

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Relative Pathnames (. and ..)

• cat /etc/service
• cat ../../etc/service
• Youll sometimes need to precede a command with
  ./ (a dot and a /).
• Assume you want to use a cat program written by
  you in the current directory, you can run your
  own cat and ignore the one in /bin
• ./cat note

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mkdir Making Directories

• Directories are created with the mkdir (make
  directory) command.
• The command is followed by the names of the
  directories to be created.
• You can create more than one directory in one
  command.
• mkdir doc src news

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mkdir Making Directories

• Sometimes, the system refuses to create a
  directory because
• The directory may already exist.
• There may be an ordinary file by that name in the
  current directory.
• The permissions set for the current directory
  dont permit the creation of files and
  directories by the user.

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rmdir Removing Directories

• The rmdir (remove directory) command removes
  directories.
• You can delete more than one directory in one
  command.
• They are two important rules when deleting
  directories
• You cant use rmdir to delete a directory unless
  it is empty.
• You cant remove a subdirectory unless you are
  placed in a directory hierarchically above the
  one you choose.

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cp Copying Files

• The cp command copies a file or a group of files.
• cp chap1 unit1
• If the destination file (unit1) doesnt exist, a
  new file will be created. If not, it will be
  overwriten without any warning from the system.
• If unit1 is a directory, the file will be copied
  into that directory.

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cp Copying Files

• You can copy multiple files to a directory.
• For instance, to copy the file chap1, chap2, and
  chap3 to the progs directory, you can use
• cp chap1 chap2 chap3 progs
• The UNIX system uses a set of special characters
  called metacharacters that you can use for
  matching more than one file.

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cp Copying Files

• cp is often used with the shorthand notation .
  (dot) to signify the current directory as the
  destination.
• For instance, to copy the file .profile from
  /home/juliet to your current directory, you can
  use either of the two commands
• cp /home/juliet/.profile .profile
• cp /home/juliet/.profile .

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cp Copying Files

• You can use the as a shorthand for multiple
  filenames sharing a command string.
• For example, you can copy chap01, chap02, and
  chap3 in this way
• copy chap progs
• The i (interactive) option warns the user before
  overwritting the destination file.
• The r (recursive) option makes it possible to
  copy an entire directory.

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rm Deleting Files

• The rm command removes files and makes space
  available on disk.
• It normally operates silently and should be used
  with caution. It can delete more than one file
  with a single instruction
• rm chap01 chap02 chap03
• rm chap
• rm progs/chap01 progs/chap02

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rm Deleting Files

• Unless used with r option, rm wont remove a
  directory.
• You may need to delete all files of a directory,
  as part of a cleaning-up operation
• rm
• The i (interactive) option makes the command ask
  the user for confirmation before removing each
  file.

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rm Deleting Files

• With the r option, rm performs a tree walk a
  thorough recursive search for all subdirectories
  and files within these subdirectories.
• Using the rm r will delete all files in the
  current directory and all subdirectories and
  their files.
• rm wont delete any file if its write-protected.
  
• The f (force) option overrides this protection
  also.