Table of Contents for
Linux Shell Scripting Bootcamp

Version ebook / Retour

Cover image for bash Cookbook, 2nd Edition Linux Shell Scripting Bootcamp by James Kent Lewis Published by Packt Publishing, 2017
  1. Cover
  2. Table of Contents
  3. Linux Shell Scripting Bootcamp
  4. Linux Shell Scripting Bootcamp
  5. Credits
  6. About the Author
  7. Acknowledgement
  8. About the Reviewer
  9. www.PacktPub.com
  10. Customer Feedback
  11. Preface
  12. What you need for this book
  13. Who this book is for
  14. Conventions
  15. Reader feedback
  16. Customer support
  17. 1. Getting Started with Shell Scripting
  18. Demonstrating the use of scripts
  19. Summary
  20. 2. Working with Variables
  21. Validating parameters using conditional statements
  22. Comparison operators for strings
  23. Environment variables
  24. Summary
  25. 3. Using Loops and the sleep Command
  26. Screen manipulation
  27. Indenting your code
  28. Using the for statement
  29. Leaving a loop early
  30. The sleep command
  31. Watching a process
  32. Creating numbered backup files
  33. Summary
  34. 4. Creating and Calling Subroutines
  35. File redirection
  36. Command piping
  37. Subroutines
  38. Using parameters
  39. Making a current backup of your work
  40. Summary
  41. 5. Creating Interactive Scripts
  42. Summary
  43. 6. Automating Tasks with Scripts
  44. Summary
  45. 7. Working with Files
  46. Reading files
  47. Reading and writing files
  48. Reading and writing files interactively
  49. File checksums
  50. File encryption
  51. Summary
  52. 8. Working with wget and curl
  53. wget and recursion
  54. wget options
  55. curl
  56. Summary
  57. 9. Debugging Scripts
  58. Automatic backups
  59. More syntax errors
  60. Logic errors
  61. Using set to debug scripts
  62. Summary
  63. 10. Scripting Best Practices
  64. ssh and scp
  65. Find and use a good text editor
  66. Environment variables and aliases
  67. ssh prompt
  68. Testing an archive
  69. Progress indicator
  70. Creating new commands from a template
  71. Alerting the user
  72. Summary
  73. Index

Chapter 4. Creating and Calling Subroutines

This chapter shows how to create and call subroutines in a script.

The topics covered in this chapter are as follows:

  • Show some simple subroutines.
  • Show more advanced routines.
  • Mention return codes again and how they work in scripts.

In the previous chapters we have seen mostly simple scripts that were not very complicated. Scripts can actually do a whole lot more which we are about to see.

First, let's start with a selection of simple but powerful scripts. These are mainly shown to give the reader an idea of just what can be done quickly with a script.

Clearing the screen

The tput clear terminal command can be used to clear the current command-line session. You could type tput clear all the time, but wouldn't just cls be nicer?

Here's a simple script that clears the current screen:

Chapter 4 - Script 1

#!/bin/sh
#
# 5/8/2017
#
tput clear

Notice that this was so simple I didn't even bother to include a Usage message or return code. Remember, to make this a command on your system do this:

  • cd $HOME/bin
  • create/edit a file named cls
  • copy and paste the preceding code into this file
  • save the file
  • run chmod 755 cls

You can now type cls from any terminal (under that user) and your screen will clear. Try it.