This book was written using Bash 4.2 and 5.0 on Linux. The majority of the contents should be applicable to versions long before and after those, and to other Unix–like operating systems. However, since everything on Linux is configurable, absolute statements such as “
$PATH will not be defined in a crontab” should be treated as a pragmatic shorthand for providing a virtual machine with the configuration I used when writing. It is not even theoretically possible to write a piece of software which will behave the same no matter how and where it is run. So the only way to know what some command will actually do is to run it, and no statement in this book should be treated as absolute truth. In the same vein, the code in this book is written to make a best effort at doing the right thing in a reasonable set of circumstances.