Directories

Your home directory is part of a fairly large directory tree which contains all user accounts, system files, and output devices.

The following commands are useful when working with directories from the Unix shell (which is usually the most efficient mode of operation):

pwd

Display current location in the directory tree.

cd directory

Change current directory. Change to home directory if no argument given.

mkdir directory

Create a new directory with the given name.

rmdir directory

Remove directory with the given name. If the directory is not empty, use rm -r instead, but make sure you know what you are deleting!

The directory argument is usually the name of a directory, but can also be one of the following abbreviations:

~

Home directory.

~xy

Home directory of the user named xy.

.

Current directory.

..

Parent directory of current directory.

Listing Files

ls

List files in current directory. Files starting with . (``dotfiles'') will not be listed.

ls -a

List all files in the current directory.

ls -l

Long list.

The long list gives file permissions (see below), number of hardlinks, owner, group, file size, modification time, and file name. The information about file permissions is very important. The format is

A dash indicates that a permission is not set. The first column entry can be one of the following:

-

Regular file.

d

File is a directory.

l

File is a soft link to another location.

c

Device file that does char I/O. (There are more device types.)

The file permissions can be changed with chmod, for example chmod u+x filename sets the execute permission for the user (i.e., for you), or chmod o-r filename revokes the read permission for other users not part of the ``group'' (for all practical purposes you should treat ``other'' and ``group'' alike). Directories must be executable!

Moving Files Around

mv source target

If target is a directory, move the source into target. Otherwise rename source into target.

rm

Delete the given file(s). There is no way to un-delete files! To delete a directory and all of its contents, use rm -r. If you don't want to be prompted for every file, use rm -f or rm -rf respectively.

cp

Copy a file, usage similar to mv.

File Name Abbreviations

• File names can be automatically completed in the shell (tcsh and bash only) by pressing TAB.
• In a file name, * matches 0 or more characters, ? matches 1 character, [abc] matches a single a, b, or c.

Archiving and Compressing files

• Creating a .tar file which contains all the files of directory:

    tar -cvpf directory.tar directory
  

• Compressing a file (for example the file directory.tar created before), the resulting file will be named filename.gz:

    gzip -v filename
  

• Uncompressing a .gz compressed file:

    gzip -dv filename.gz
  

• Unpacking a .tar archive file:

    tar -xvpf directory.tar
  

Manual Pages

man command

Displays the ``manual page'' for command.

apropos keyword

Displays a list of commands that have to do with keyword.

Pipes, redirection, greping

> <

redirection of stdout or stdin

|

``piping'' output of one process into another

grep

looks for a string in a file or files.

Examples:

grep alias .cshrc

searches for string ``alias'' in the file .cshrc

ls -l | grep dr

gives a list of directories

grep John *

looks for ``John'' in all files of current directory

ps -ef | sort

gives a sorted list of processes running on your machine.