This book is relevant to all versions of bash , although older versions lack some of the features of the most recent version.  You can easily find out which version you are using by typing echo $BASH_VERSION . The earliest public version of bash was 1.0, and the most recent is 2.01 (released in May 1997). If you have an older version, you might like to upgrade to the latest one. Chapter 11 , shows you how to go about it.
 Even though version 2.0 has been out for a while, bash version 1.14. x is still in widespread use. Throughout this book we have clearly marked with footnotes the features that are not present in the earlier versions.