Introduction to Unix

4. The Shells

In Linux for Programmers and Users Chapter 5, we take a closer look at what the shell does for us. Of necessity, we have already used many of the shell discussed here. We will thus clarify some concepts and present several new features of the shell. Many of commands presented here are commands that are built into the shell. The commands from Chapter 5 that are stand alone programs are ones that relate to how commands are entered to the shell. We also introduce shell script programming, which is covered in more detail in Chapter 6.

Contents

• 4.1. A Choice of Shells
  • 4.1.1. A Bit of Shell History
  • 4.1.2. chsh
• 4.2. echo
  • 4.2.1. Escaped Characters
• 4.3. Shell Metacharacters
  • 4.3.1. How to Avoid Shell Interpretation
• 4.4. Here Documents
  • 4.4.1. Strip Leading Tabs
• 4.5. File Redirection
  • 4.5.1. stdin Redirection
  • 4.5.2. stdout Redirection
  • 4.5.3. stderr Redirection
• 4.6. Filename Substitution (Wildcards)
• 4.7. The Pipe (|)
• 4.8. tee
• 4.9. sleep
• 4.10. Command Substitution
• 4.11. Sequences of Commands
  • 4.11.1. Conditional Execution
• 4.12. Shell Variables
  • 4.12.1. export
  • 4.12.2. env
  • 4.12.3. Command Line Arguments
  • 4.12.4. shift
  • 4.12.5. Exit Code
• 4.13. Job or Process Control
  • 4.13.1. Background Processes
  • 4.13.2. ps
  • 4.13.3. kill
  • 4.13.4. jobs
  • 4.13.5. fg
  • 4.13.6. bg
  • 4.13.7. nohup
• 4.14. A Shell Script Program
• 4.15. source