Bash Shell

Bash is the default shell, or command interpreter, for the GNU/Linux. In shell, you have a current working directory and many commands use that as a hidden parameter. When you have to type a file or a directory you can use auto-completion, by typing the first letters of the file or directory and then pressing TAB. If you typed a command that needs a parameter file or directory you can press TAB twice to list all the files or directories in the current directory.

You can use up-arrow and down-arrow to navigate through the history of all the commands that you previously typed.

Notation

In the following description C-<chr> means hold the CONTROL key while typing the character <chr>. Thus, C-f would be: hold the CONTROL key and type f.

You can use C-r to search backwards through the list to previously typed commands. Typing C-r again will go to the previous matching command, C-s will go to the next matching command. C-g will cancel your search, ENTER will execute the command.

Directories

There are the following special directory names:

home directory: ~ (tilde)
parent directory: .. (two dots)
current directory: . (dot)

Commands:

Print current working directory: pwd
Change the current working directory: cd <dir>
Make directory: mkdir <dir>
Remove an empty directory: rmdir <dir>

Files

Files and directories that start with a . (dot) are usually system files and are hidden from the list command.

List files in a directory: ls [-a] <dir> Without any parameter the command lists the current working directory. If you add the -a switch, all the files, including the hidden ones will be listed.
Copy: cp <src> <dest> copy source file to destination file, cp <file1> <file2> ... <dir> copy source files to directory, cp -r <src_dir> <dest_dir> copy recursively source directory to destination directory.
Remove: rm <file>. Warning: there is no undo!
Move (Rename): mv <src> <dest>

File access permissions

There are three kinds of entities that can access files and directories: the user who created the file, users that are part of the same group as the user who created the file, and other users.

There are three kinds of access that can be allowed for every of the three entities that can access a file: r entity can read the file or directory, w entity can write the file or directory, x entity can execute the file or change into directory.

You can use ls -l to list files and access permissions. The command used to change the access permissions to a file is called chmod, and you can use + to allow access, and - to disallow access. Examples:

chmod go+x ~: Allow group and other to change into home directory
chmod go+rx public_html: Allow group and other to change into and read directory public_html

Programs