LINUX | Files | Directories | Programs | Expressions | Utilities | Shell Scripts
LINUX is a computer operating system. LINUX also refers to the kernel, which the operating system is built on. LINUX is built similar to UNIX, but written and distributed under the GNU General Public License as declared by the FSF.
A shell is a program with a CUI (character user interface) that interprets and sends user commands to the kernel. Several shells are included with LINUX, each with a command name...
sh - Bourne Shell (original)
bash - Bourne Again Shell (most common)
ksh - Korn Shell (advanced)
zsh - Z Shell (advanced)
csh - C Shell (in C syntax)
tcsh - TC Shell (in C syntax)
The default shell in LINUX can be changed. One or more shells can run at the same time. The bash shell is the most common and used in the tutorials.
PuTTY is a SSH (secure shell) and Telnet (telecommunication network) client for interacting remotely with LINUX, commonly with Linux on Windows. SSH and Telnet are network protocols used for Internet and LAN (local area network) connections. SSH is a secure form of Telnet.
A path is a way of navigating through files and directories in a shell. The root directory is the source directory that stores all other files and directories, as declared by the / forward slash operator. The / also connects directory and file names in a path. An absolute path starts from the root directory...
/home/directoryName1/fileName1
A relative path starts from the home or present directory...
directoryName1/fileName1
Users are in the home directory by default when logging in. The PWD (present working directory) is any directory the user is currently in. Other operators can be used in paths...
./ references the PWD
../ references the parent directory
~/ references the home directory
Users enter commands into a shell to access programs. Commands are coded as ASCII plain text and are case sensitive. Commands are modified with options and arguments to execute a variety of processes. A command line is initiated by a $ prompt symbol. The prompt symbol varies depending on the system...
Each position in a command line follows general syntax rules.
Commands...
Options...
Arguments...
An external command is interpreted by a file.
An internal command is interpreted by the shell.
