LPI Linux Certification in a Nutshell, 2nd Edition

GNU and Unix Commands

Objective 1: Work Effectively on the Command Line

The interactive shell and shell variables

• A shell provides the command prompt and interprets commands.

• A shell variable holds a value that is accessible to shell programs.

• PATH is a shell variable that contains a listing of directories that hold executable programs.

• Commands must be bash built-ins, found in the PATH, or explicitly defined in order to succeed.

• When shell variables are exported, they become part of the environment.

Entering commands

• Commands are comprised of a valid command, with or without one or more options and arguments, followed by a carriage return.

• Interactive commands can include looping structures more often used in shell scripts.

Command history, editing, and substitution

• Shell sessions can be viewed as a conversation. History, expansion, and editing make that dialog more productive.

• Commands can be reissued, modified, and edited. Examples are shown in Table 10-2.

• Command substitution allows the result of a command to be placed into a shell variable.

Table 10-2. Shell expansion, editing, and substitution examples

History type	Examples
Expansion	!!
	!n
	^string1^string2
Editing	Ctrl-P, previous line
	Ctrl-K, kill to end of line
	Ctrl-Y, paste (yank) text
Substitution	VAR=$(command)

Recursive execution

• Many commands contain either a -r or -R option for recursive execution through a directory hierarchy.

• The find command is inherently recursive, and is intended to descend through directories ...