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Book: LPI Linux Certification in a Nutshell Section: Chapter 24. Exam 102 Highlighter's Index
24.5 Shells, Scripting, Programming, and Compiling 24.5.1 Objective 1: Customize and Use the Shell Environment -
A shell presents an interactive Textual User Interface, an operating environment, a facility for launching programs, and a programming language. -
Shells can generally be divided into those derived from the Bourne shell, sh (including bash), and the C-shells, such as tcsh. -
Shells are distinct from the kernel and run as user programs. -
Shells can be customized by manipulating variables. -
Shells use configuration files at startup. -
Shells pass environment variables to child processes, including other shells. 24.5.1.1 bash -
bash is a descendant of sh. -
Shell variables are known only to the local shell and are not passed on to other processes. -
Environment variables are passed on to other processes. -
A shell variable is made an environment variable when it is exported. -
This sets a shell variable: # PI=3.14 Table 24-3. Bash Configuration Files /etc/profile | The system-wide initialization file; executed when you log in. | /etc/bashrc | Another system-wide initialization file; may be executed by a user's .bashrc for each bash shell launched. | ~/.bash_profile | If this file exists, it is executed automatically after /etc/profile when you log in. | ~/.bash_login | If .bash_profile doesn't exist, this file is executed automatically when you log in. | ~/.profile | If neither .bash_profile nor .bash_login exists, this file is executed automatically when you log in. | ~/.bashrc | This file is executed automatically when bash starts. | ~/.bash_logout | This file is executed automatically when you log out. | ~/.inputrc | This file contains optional key bindings and variables that affect how bash responds to your keystrokes. | 24.5.2 Objective 2: Customize or Write Simple Scripts -
Scripts are executable text files containing commands. -
Scripts must have appropriate execution bits set in the mode. -
Some scripts define the interpreter using the #!/bin/bash syntax on the first line. 24.5.2.1 Environment -
A script that starts using #!/bin/bash operates in a new invocation of the shell. This shell first executes standard system and user startup scripts. It also inherits exported variables from the parent shell. -
Like binary programs, scripts can offer a return value after execution. -
Scripts use file tests to examine and check for specific information on files. -
Scripts can use command substitution to utilize the result of an external command. -
Scripts often send email to notify administrators of errors or status. -
Refer to Chapter 17 for details on bash commands. | | |
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