Book Image

Linux Command Line and Shell Scripting Bible - Third Edition

By : Richard Blum, Christine Bresnahan
Book Image

Linux Command Line and Shell Scripting Bible - Third Edition

By: Richard Blum, Christine Bresnahan

Overview of this book

The Linux command line enables you to type specific shell commands directly into the system to manipulate files and query system resources. Command line statements can be combined into short programs called shell scripts, a practice increasing in popularity due to its usefulness in automation. Linux is a robust system with tremendous potential, and Linux Command Line and Shell Scripting Bible opens the door to new possibilities. Linux Command Line and Shell Scripting Bible is your essential Linux guide. It contains new functional examples that are fully updated to align with the latest Linux features. Beginning with command line fundamentals, the book moves into shell scripting and shows you the practical application of commands in automating frequently performed functions. This book is a complete guide providing detailed instruction and expert advice working within this aspect of Linux. Whether used as a tutorial or as a quick reference, this book contains information that every Linux user should know.
Table of Contents (34 chapters)
Part I: The Linux Command Line
Part II: Shell Scripting Basics
Part III: Advanced Shell Scripting
Part IV: Creating Practical Scripts
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This chapter discussed the complicated interactive program, the GNU bash shell. It covered understanding the shell process and its relationships, including how subshells are spawned and their relationship to the parent shell. We also explored commands that create child processes and commands that don't.

The default interactive shell is normally started whenever a user logs in to a terminal. The shell that the system starts depends upon a user ID configuration. Typically, it is /bin/bash. The default system shell, /bin/sh, is used for system shell scripts, such as those needed at startup.

A subshell or child shell can be spawned using the bash command. They are also created when a process list or the coproc command is used. Using subshells at the command line can allow for creative and productive use of the CLI. Subshells can be nested, spawning grandchild shells and great-grandchild shells. Creating a subshell is an expensive process as a new environment for the shell must...