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Linux System Programming Techniques

You're reading from   Linux System Programming Techniques Become a proficient Linux system programmer using expert recipes and techniques

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Product type Paperback
Published in May 2021
Publisher Packt
ISBN-13 9781789951288
Length 432 pages
Edition 1st Edition
Tools
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Author (1):
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Jack-Benny Persson Jack-Benny Persson
Author Profile Icon Jack-Benny Persson
Jack-Benny Persson
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Toc

Table of Contents (14) Chapters Close

Preface 1. Chapter 1: Getting the Necessary Tools and Writing Our First Linux Programs 2. Chapter 2: Making Your Programs Easy to Script FREE CHAPTER 3. Chapter 3: Diving Deep into C in Linux 4. Chapter 4: Handling Errors in Your Programs 5. Chapter 5: Working with File I/O and Filesystem Operations 6. Chapter 6: Spawning Processes and Using Job Control 7. Chapter 7: Using systemd to Handle Your Daemons 8. Chapter 8: Creating Shared Libraries 9. Chapter 9: Terminal I/O and Changing Terminal Behavior 10. Chapter 10: Using Different Kinds of IPC 11. Chapter 11: Using Threads in Your Programs 12. Chapter 12: Debugging Your Programs 13. Other Books You May Enjoy

Moving around inside a file with lseek()

In this recipe, we'll learn how to move around inside a file with lseek(). This function operates on file descriptors, so please note that we are now working with file descriptors, not streams. With lseek(), we can move around (or seek) freely inside a file descriptor. Doing so can be handy if we only want to read a specific part of a file or we want to go back and read some data twice and so on.

In this recipe, we will modify our previous program, called fd-read.c, to specify where we want to start reading. We also make it so that the user can specify how many characters should be read from that position.

Getting ready

To easier understand this recipe, I encourage you to read the recipe named Reading from files with file descriptors in this chapter before reading this one.

How to do it…

The program we will write here will read a file using file descriptors. The user must also set a starting position where the read...

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