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CS 497C – Introduction to UNIX Lecture 12: - The File System

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 with respect to the current directory.

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CS 497C – Introduction to UNIX Lecture 12: - The File System

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  1. CS 497C – Introduction to UNIXLecture 12: - The File System Chin-Chih Changchang@cs.twsu.edu

  2. 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.

  3. 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:

  4. Relative Pathnames (. and ..) $ cat /etc/service $ cat ../../etc/service • You’ll 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

  5. 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

  6. 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.

  7. 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.

  8. 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.

  9. 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.

  10. 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 .

  11. 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.

  12. 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

  13. 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.

  14. 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.

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