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 pipes

In some cases, we may store output from one command in a file, with the intent to use it in the input to another. Consider this script, which accepts a list of ASCII words on its standard input, converts any uppercase letters to lowercase with tr, sorts them, and then prints a count of how often each word is used, sorted by frequency:


# Convert all capital letters in the input to lowercase tr A-Z a-z > words.lowercase

# Sort all the lowercase words in order sort words.lowercase > words.sorted

# Print counts of how many times each word occurs uniq -c words.sorted > words.frequency

# Sort that list by frequency, descending sort -k1,1nr words.frequency

This sort of script involving many commands in sequence to filter and aggregate data can be very useful for analyzing large amounts of raw text, such as log files. However, there's a problem; when...