Aug 29

Login/Logout

enter your login name (echoed to screen), hit <enter>, enter your password (not echoed), hit <enter>. Open up a shell (terminal) window to type commands.

Directories (branches) contain either files or subdirectories (branches of branches). A file system is usually viewed as an inverted (upside down) tree.
- Highest level directory = root /
- User's home directory, e.g., /home/<yourlogin> is typically what you start out with, when you open a shell.

Pathname: filename preceded by directories leading to the file.
- Absolute pathname: the complete pathname of a file starting with the root /.
- Relative pathname: pathname that implicitly starts at the working directory,

Special Directories: Every directory contains at least two subdirectories: "." and ".."
- . is an abbreviation for the current working directory; stores location of current directory.
- .. is an abbreviation for the directory containing the current working directory (i.e., its parent); stores location of parent directory.

Below pathnames to <file> or <dir> can be absolute or relative.

`cd <dir>`	Change directory: change directory to <`dir`> alters working directory; used to traverse Unix hierarchical tree file structure.
`cd`	change to home directory (useful if you get lost)
`cd ..`	changes to parent directory of working directory
`cd ~<loginid>`	change to home directory of user with login<loginid>

pwd - print working directory, displays current working directory path.
ls - list, list directory contents; ls without a directory argument defaults to the current directory, as do most Unix commands.
cat <file> concatenate: displays contents of file.
touch <file> creates the file (if it doesn't already exist). If it exists already, touch might seem to be doing nothing (but later we will understand more clearly what it has done).
mkdir <dirname> creats a directory.