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.
|Free Today: September Issue of Linux Journal (Retail value: $5.99)||Sep 27, 2016|
|nginx||Sep 27, 2016|
|Epiq Solutions' Sidekiq M.2||Sep 26, 2016|
|Nativ Disc||Sep 23, 2016|
|Android Browser Security--What You Haven't Been Told||Sep 22, 2016|
|The Many Paths to a Solution||Sep 21, 2016|
- Android Browser Security--What You Haven't Been Told
- Readers' Choice Awards 2013
- Epiq Solutions' Sidekiq M.2
- Free Today: September Issue of Linux Journal (Retail value: $5.99)
- Nativ Disc
- The Many Paths to a Solution
- Synopsys' Coverity
- Download "Linux Management with Red Hat Satellite: Measuring Business Impact and ROI"
- Returning Values from Bash Functions
Pick up any e-commerce web or mobile app today, and you’ll be holding a mashup of interconnected applications and services from a variety of different providers. For instance, when you connect to Amazon’s e-commerce app, cookies, tags and pixels that are monitored by solutions like Exact Target, BazaarVoice, Bing, Shopzilla, Liveramp and Google Tag Manager track every action you take. You’re presented with special offers and coupons based on your viewing and buying patterns. If you find something you want for your birthday, a third party manages your wish list, which you can share through multiple social- media outlets or email to a friend. When you select something to buy, you find yourself presented with similar items as kind suggestions. And when you finally check out, you’re offered the ability to pay with promo codes, gifts cards, PayPal or a variety of credit cards.Get the Guide