Work the Shell - Handling Errors and Making Scripts Bulletproof
Finally, another thing to be aware of with the shell is that it's all too easy to zap important files with a redirect. For example, this shouldn't work:
$ who > who.output $ ls > who.output
The second command should generate an error because the output file already exists, right? But it doesn't, and it simply trashes the who output without a warning or error—not good.
To avoid that problem, you'll want to set -o noclobber in scripts or, better, for your login shell, and let it be inherited by subshells, including those that run your shell scripts. A good place to put it could be in your .profile or .bashrc.
With noclobber set, the two commands behave differently:
$ ls > who.output -bash: who.output: cannot overwrite existing file
That's useful for everyone, and doubly so for us shell script hackers, right?
Dave Taylor is a 26-year veteran of UNIX, creator of The Elm Mail System, and most recently author of both the best-selling Wicked Cool Shell Scripts and Teach Yourself Unix in 24 Hours, among his 16 technical books. His main Web site is at www.intuitive.com, and he also offers up tech support at AskDaveTaylor.com. Follow him on Twitter if you'd like: twitter.com/DaveTaylor.
Dave Taylor has been hacking shell scripts for over thirty years. Really. He's the author of the popular "Wicked Cool Shell Scripts" and can be found on Twitter as @DaveTaylor and more generally at www.DaveTaylorOnline.com.
|Raspi-Sump||Dec 16, 2014|
|diff -u: What's New in Kernel Development||Dec 12, 2014|
|Non-Linux FOSS: Don't Type All Those Words!||Dec 10, 2014|
|Computing without a Computer||Dec 08, 2014|
|Autokey: Shorthand for Typists||Dec 04, 2014|
|How Can We Get Business to Care about Freedom, Openness and Interoperability?||Dec 03, 2014|
- Cooking with Linux - Serious Cool, Sysadmin Style!
- Readers' Choice Awards 2014
- diff -u: What's New in Kernel Development
- How Can We Get Business to Care about Freedom, Openness and Interoperability?
- Synchronize Your Life with ownCloud
- Days Between Dates?
- Non-Linux FOSS: Don't Type All Those Words!
- New Products
- Computing without a Computer
Editorial Advisory Panel
Thank you to our 2014 Editorial Advisors!
- Jeff Parent
- Brad Baillio
- Nick Baronian
- Steve Case
- Chadalavada Kalyana
- Caleb Cullen
- Keir Davis
- Michael Eager
- Nick Faltys
- Dennis Frey
- Philip Jacob
- Jay Kruizenga
- Steve Marquez
- Dave McAllister
- Craig Oda
- Mike Roberts
- Chris Stark
- Patrick Swartz
- David Lynch
- Alicia Gibb
- Thomas Quinlan
- Carson McDonald
- Kristen Shoemaker
- Charnell Luchich
- James Walker
- Victor Gregorio
- Hari Boukis
- Brian Conner
- David Lane