LPI Linux Certification in a Nutshell, 2nd Edition

Shells, Scripting, Programming, and Compiling

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.

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

• This turns it into an environment variable:

  # export PI

• This definition does both at the same time:

  # export PI=3.14

• Shell aliases conveniently create new commands or modify existing commands:

  # alias more='less'

• Functions are defined for and called in scripts. This line creates a function named lsps:

  # lsps ( ) { ls -l; ps; }

• bash configuration files control the shell's behavior. Table 17-1 contains a list of these files.

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 ...