Book Image

Bash Quick Start Guide

By : Tom Ryder
Book Image

Bash Quick Start Guide

By: Tom Ryder

Overview of this book

Bash and shell script programming is central to using Linux, but it has many peculiar properties that are hard to understand and unfamiliar to many programmers, with a lot of misleading and even risky information online. Bash Quick Start Guide tackles these problems head on, and shows you the best practices of shell script programming. This book teaches effective shell script programming with Bash, and is ideal for people who may have used its command line but never really learned it in depth. This book will show you how even simple programming constructs in the shell can speed up and automate any kind of daily command-line work. For people who need to use the command line regularly in their daily work, this book provides practical advice for using the command-line shell beyond merely typing or copy-pasting commands into the shell. Readers will learn techniques suitable for automating processes and controlling processes, on both servers and workstations, whether for single command lines or long and complex scripts. The book even includes information on configuring your own shell environment to suit your workflow, and provides a running start for interpreting Bash scripts written by others.
Table of Contents (10 chapters)

Using temporary files cleanly

If you need a temporary file in your script to store data for the script's run, it can be tempting to assume a fixed path for the file in /tmp:

# Store the current date for later
# Requires GNU/BSD `date` with non-POSIX %s format
date +%s > /tmp/myscript-timestamp

/tmp exists on virtually all Unix systems, which makes it a popular choice. However, this approach has some risks:

  • There may be a safer or more suitable location for temporary files specified by the system, or preferred by the user, such as /var/tmp. The /tmp directory might be very strictly locked down in some environments, especially PCI-DSS-compliant systems.
  • If the temporary filename name is not unique, and more than one instance of the script runs at once, the behavior can be unpredictable and hard to debug.
  • Because /tmp is world-writable, if an attacker can write to and predict...