Work the Shell - Understanding Exit Codes
Now that you know how to capture and analyze the exit codes from system commands, what if you want to have the error message be one from your script, not one from the command itself?
That's done with another new shorthand notation: >&, which redirects the stderr/error output stream. Here's how I use that to hide all error messages from the mkdir command being used in our sample scripts:
mkdir /usr >& /dev/null
You also can use &> or 2>&1 instead of >&.
If you don't test the results of the command, of course, you seriously can hose things up, but this makes the output more elegant for sure:
$ ./test.sh mkdir /usr failed: we have an exit code of 0
Hmmm...I'm still getting that false 0. Oh! I haven't added the code to save the exit code value as “error”. One slight tweak later and:
$ ./test.sh mkdir /usr failed: we have an exit code of 1
That's more like it!
I'm going to call this a wrap for this month. Next month, I'll demonstrate how the exit command lets you send exit codes back to the calling program from procedures and functions, just as if they were separate Linux commands rather than part of the same shell script.
Dave Taylor has been hacking shell scripts for a really long time, 30 years. He's the author of the popular Wicked Cool Shell Scripts, and he can be found on Twitter as @DaveTaylor and more generally at www.DaveTaylorOnline.com.
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.
Fast/Flexible Linux OS Recovery
On Demand Now
In this live one-hour webinar, learn how to enhance your existing backup strategies for complete disaster recovery preparedness using Storix System Backup Administrator (SBAdmin), a highly flexible full-system recovery solution for UNIX and Linux systems.
Join Linux Journal's Shawn Powers and David Huffman, President/CEO, Storix, Inc.
Free to Linux Journal readers.Register Now!
- Petros Koutoupis' RapidDisk
- Download "Linux Management with Red Hat Satellite: Measuring Business Impact and ROI"
- The Italian Army Switches to LibreOffice
- Linux Mint 18
- Oracle vs. Google: Round 2
- The FBI and the Mozilla Foundation Lock Horns over Known Security Hole
- Varnish Software's Varnish Massive Storage Engine
- Firefox 46.0 Released
- Ubuntu Online Summit
Until recently, IBM’s Power Platform was looked upon as being the system that hosted IBM’s flavor of UNIX and proprietary operating system called IBM i. These servers often are found in medium-size businesses running ERP, CRM and financials for on-premise customers. By enabling the Power platform to run the Linux OS, IBM now has positioned Power to be the platform of choice for those already running Linux that are facing scalability issues, especially customers looking at analytics, big data or cloud computing.
￼Running Linux on IBM’s Power hardware offers some obvious benefits, including improved processing speed and memory bandwidth, inherent security, and simpler deployment and management. But if you look beyond the impressive architecture, you’ll also find an open ecosystem that has given rise to a strong, innovative community, as well as an inventory of system and network management applications that really help leverage the benefits offered by running Linux on Power.Get the Guide