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)

Looping over shell words with for

The for keyword is used to define code to run repeatedly over a list of shell words:

for system in bsd linux macosx windows ; do
    printf '%s\n' "${system^^}"

The preceding code loops through the list of four items, assigning each one in turn to the system variable. The body of the loop prints the value of the system variable in all caps, for each iteration of the loop.

Note the following about the preceding syntax:

  • The variable name goes just after for, and before in
  • do is required and needs to be after the semicolon, to specify where the variable and list of words finishes
  • The loop is closed with done, not rof as you might have expected from fi and esac
  • The list of words can be blank; for system in ; do ... ; done is not a syntax error, it just does nothing

The assignment of the system variable in this...