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)

Redirecting errors

If you experiment with redirecting the output of commands to files, you may find that error messages are still written to your terminal instead of the destination you specified:

$ grep pattern myfile /nonexistent > matches
grep: /nonexistent: No such file or directory

This is an intentional design feature of Unix-like operating systems, not just the bash program; it's to separate the output of commands (standard output, or stdout) from any error messages the command may also generate (standard error, or stderr). It's very common for commands to emit both output and error messages, so that the person running the script can read the errors without it interfering with any output from the script.

If you want to redirect error messages as well, the syntax is slightly different; you need to link the redirection operator with the standard error stream...