December 2025
Intermediate to advanced
704 pages
15h 22m
English
Content preview from Linux Command Line and Shell Scripting Bible, 5th Edition
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Chapter 5Understanding the Shell
Now that you know a few shell basics, such as reaching the shell and rudimentary commands, it’s time to explore the actual shell process. To understand it, you need to know how it operates in different circumstances.
A shell is not just a CLI. It is a complicated interactive running program. Entering commands and using the shell to run scripts can raise some interesting and confusing issues. Understanding the shell process and its relationships helps you resolve these issues or avoid them altogether.
This chapter takes you through learning about the shell process and how it operates in various situations. You explore how subshells are created as well as the relationship to their parent shell. The different commands that create child processes are examined along with those that don’t (built-in commands). The chapter also covers some shell tips and tricks you can try to make your CLI experience more productive.
Investigating Shell Types
The shell program that the system starts when you log into the system depends on your user ID configuration. In the /etc/passwd file, the user ID has its default shell program listed in field #7 of its entry. This default shell program is started when the user either logs into a virtual console terminal or starts a terminal emulator in the GUI.
In the following ...
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