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 Bash's C-style for loops

Bash extends the for keyword to provide functionality similar to the three-argument for loop used in C:

for ((i = 1 ; i <= 10 ; i++)) ; do
    printf '%u\n' "$i"

The preceding code prints the numbers from 1 to 10, each terminated by a newline, by assigning each number to the i variable in turn and then printing it. When followed by an unquoted ((, the meaning of for changes; it does not iterate over a list of words, but instead loops using the three semicolon-separated statements in the double parentheses like so:

  • The first expression is run before the loop starts: We assign the i value to zero to start it off.
  • The second expression is the test used to determine whether the loop should continue or stop: We test whether the value of i is less than 10.
  • The third expression runs after each instance of the...