CS 497C - Introduction to UNIX
Lecture 12: - The File System
Chin-Chih Chang chang@cs.twsu.edu

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

Relative Pathnames (. and ..)
$ pwd
/home/remeo/progs
$ cd ../..
$ pwd
/home
* You'll sometimes need to precede a command with ./ (a dot and a /).

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

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 don’t permit the 
   creation of files and directories by the user.

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 can’t use rmdir to delete a directory unless it is empty. 
 - You can’t remove a subdirectory unless you are placed in a directory 
   hierarchically above the one you choose.

cp: Copying Files
* The cp command copies a file or a group of files.
cp chap1 unit1
* If the destination file (unit1) doesn't 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.

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.

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 .

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.

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

rm: Deleting Files
* Unless used with -r option, rm won't 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.

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 won't delete any file if it's write-protected. 
* The -f (force) option overrides this protection also.