Robust expansion (i.e. crash) of bash variables with a typo

set -eu
By default bash expands an unbound variable to an empty string. This can be dangerous, if a critical variable name (a path prefix for example) has a typo. The -u option causes bash to treat this as an error, and the -e option causes it to exit in case of an error. These two together will make your scripts a lot safer against typos. The default behaviour can be explicitly requested using the ${NAME:-} syntax. A (less explicit) variation: #!/bin/bash -eu
Sample Output
$ cat safe-cacheclean.sh 
#!/bin/bash

set -eu
CACHEDIR=mycache
# a dangerous-looking typo, is /bin going to disappear:
rm -rf "$CACHEDI/bin"

$ ./safe-cacheclean.sh 
./safe-cacheclean.sh: line 7: CACHEDI: unbound variable

8
By: wipu
2010-04-07 11:54:40
set

What Others Think

The -e and -u options are POSIX standard, so they should work with any /bin/sh, not just bash.
inof · 661 weeks ago
Btw, you need to be careful with commands like grep and find that exit with nonzero when they don't find anything. To make matters worse, failures like these are completely silent. These kinds of commands need to be "guarded" by e.g. adding '|| echo "Nothing found"' or something after them. IMHO this kind of problem is less dangerous and easier to solve than the problems caused by not using set -eu, though.
wipu · 583 weeks and 2 days ago
Have you ever encountered a problem that seemed out of your control? And how do you deal with them? Have you really focused on entertainment? Or do you just take a break from work and still think about it? Impossible Game will be the solution to help you forget everything to have a time of real entertainment, and also a way for you to know where your limits are!
KevinDurant · 52 weeks and 1 day ago
https://seofox.ir/seo-principles/https://seofox.ir/seo-checklist/https://seofox.ir/seo/https://seofox.ir/seo-contract/https://seofox.ir/https://seofox.ir/gray-hat-seo/https://seofox.ir/robots/https://seofox.ir/link-farm-and-content-farm/https://seofox.ir/keyword-density/https://seofox.ir/search-engine/https://seofox.ir/backlink/https://seofox.ir/analyze-seo/https://seofox.ir/page-rank/https://seofox.ir/proposal/https://seofox.ir/white-hat-seo/https://seofox.ir/ugc-keyword-research/https://seofox.ir/backlink-definition/https://seofox.ir/seo-company/https://seofox.ir/googlebot/https://seofox.ir/page-speed/https://seofox.ir/broken-link/https://seofox.ir/seo-techniques/https://seofox.ir/meta-description/https://seofox.ir/ctr/https://seofox.ir/sandbox/https://seofox.ir/anchor-text/https://seofox.ir/rankbrain/https://seofox.ir/long-tail-keywords/https://seofox.ir/google-panda/https://seofox.ir/page-title/https://seofox.ir/content-marketing/https://seofox.ir/order/https://seofox.ir/redirect/https://seofox.ir/technical-seo/https://seofox.ir/on-page-seo/https://seofox.ir/seo-tools/https://seofox.ir/branding/https://seofox.ir/link-building/https://seofox.ir/off-page-seo/https://seofox.ir/seo-consultation/https://seofox.ir/on-page-seo/https://seofox.ir/local-seo/https://seofox.ir/wordpress-seo-plugin/https://seofox.ir/seo-services-prices/https://seofox.ir/google-seo-book/https://seofox.ir/start-seo/https://seofox.ir/seo-periodic-table/https://seofox.ir/content-vs-link/https://seofox.ir/social-marketing/https://seofox.ir/serpmojo/https://seofox.ir/spam-links-disavow/https://seofox.ir/google-penalty-removal/https://seofox.ir/h1/https://seofox.ir/google-penguin/https://seofox.ir/seo-articels/https://seofox.ir/what-is-google-dance/https://seofox.ir/bing/https://seofox.ir/rules-of-link-building/https://seofox.ir/seo-news/https://seofox.ir/what-is-domain-authority-and-page-authority/https://seofox.ir/template/https://seofox.ir/what-is-content-marketing/https://seofox.ir/host/https://seofox.ir/add-site-in-google/https://seofox.ir/domain-seo/https://seofox.ir/nofollow-links/https://seofox.ir/seo-portfolio/https://seofox.ir/contact-us/https://seofox.ir/faq/https://seofox.ir/privacy-policy/https://seofox.ir/terms/https://seofox.ir/about-us/https://seofox.ir/category/google-algorithms/https://seofox.ir/category/backlink/https://seofox.ir/category/blog/https://seofox.ir/category/services/https://seofox.ir/category/seo/https://seofox.ir/category/seo-content/https://seofox.ir/category/seo-resources/https://seofox.ir/category/search-engine/https://seofox.ir/seo-training/https://seofox.ir/seo-services/https://seofox.ir/faq/https://seofox.ir/contact-us/https://seofox.ir/about-us/https://seofox.ir/privacy-policy/https://seofox.ir/terms/ ????? ??? ????? ????? SEO - ????? ???? ????? ????? ????? ??? ????? ????? SEO - ????? ???? ????? ????? ????? ??? ????? ????? SEO - ????? ???? ????? ????? ????? ??? ????? ????? SEO - ????? ???? ????? ????? ????? ??? ????? ????? SEO - ????? ???? ????? ????? ????? ??? ????? ????? SEO - ????? ???? ????? ????? ????? ??? ????? ???? SEO ????? ????? ????? ???? ????? ????? ??? ???? ???? ??????? Search Engine Optimization ??? ????? ??????????? ?? ????? ?????????? ????? ????? ?? ???? ???SEO
seofox · 44 weeks and 1 day ago
Seofox.ir Seofox.ir Seofox.ir Seofox.ir Seofox.ir Seofox.ir Seofox.ir Seofox.ir Seofox.ir Seofox.ir Seofox.ir Seofox.ir Seofox.ir Seofox.ir Seofox.ir Seofox.ir Seofox.ir Seofox.ir Seofox.ir Seofox.ir Seofox.ir Seofox.ir Seofox.ir Seofox.ir Seofox.ir Seofox.ir Seofox.ir Seofox.ir Seofox.ir Seofox.ir Seofox.ir Seofox.ir Seofox.ir Seofox.ir Seofox.ir Seofox.ir Seofox.ir Seofox.ir Seofox.ir Seofox.ir Seofox.ir Seofox.ir Seofox.ir Seofox.ir Seofox.ir Seofox.ir Seofox.ir Seofox.ir Seofox.ir Seofox.ir Seofox.ir Seofox.ir Seofox.ir Seofox.ir Seofox.ir Seofox.ir Seofox.ir Seofox.ir Seofox.ir Seofox.ir Seofox.ir Seofox.ir Seofox.ir Seofox.ir Seofox.ir Seofox.ir Seofox.ir Seofox.ir Seofox.ir Seofox.ir Seofox.ir Seofox.ir Seofox.ir Seofox.ir Seofox.ir Seofox.ir Seofox.ir Seofox.ir Seofox.ir Seofox.ir Seofox.ir Seofox.ir Seofox.ir Seofox.ir Seofox.ir Seofox.ir Seofox.ir Seofox.ir Seofox.ir Seofox.ir Seofox.ir Seofox.ir Seofox.ir Seofox.ir Seofox.ir Seofox.ir Seofox.ir Seofox.ir Seofox.ir Seofox.ir Seofox.ir Seofox.ir Seofox.ir Seofox.ir Seofox.ir Seofox.ir Seofox.ir Seofox.ir Seofox.ir Seofox.ir Seofox.ir Seofox.ir Seofox.ir Seofox.ir Seofox.ir Seofox.ir Seofox.ir Seofox.ir Seofox.ir Seofox.ir Seofox.ir Seofox.ir Seofox.ir Seofox.ir Seofox.ir Seofox.ir Seofox.ir Seofox.ir Seofox.ir Seofox.ir Seofox.ir Seofox.ir Seofox.ir Seofox.ir Seofox.ir Seofox.ir Seofox.ir Seofox.ir Seofox.ir Seofox.ir Seofox.ir Seofox.ir Seofox.ir Seofox.ir Seofox.ir Seofox.ir Seofox.ir Seofox.ir Seofox.ir Seofox.ir Seofox.ir Seofox.ir Seofox.ir Seofox.ir Seofox.ir Seofox.ir Seofox.ir Seofox.ir Seofox.ir Seofox.ir Seofox.ir Seofox.ir Seofox.ir Seofox.ir Seofox.ir Seofox.ir Seofox.ir Seofox.ir Seofox.ir Seofox.ir Seofox.ir Seofox.ir Seofox.ir Seofox.ir Seofox.ir Seofox.ir Seofox.ir Seofox.ir Seofox.ir Seofox.ir Seofox.ir Seofox.ir Seofox.ir Seofox.ir Seofox.ir Seofox.ir Seofox.ir Seofox.ir Seofox.ir Seofox.ir Seofox.ir Seofox.ir Seofox.ir Seofox.ir Seofox.ir Seofox.ir Seofox.ir Seofox.ir Seofox.ir Seofox.ir Seofox.ir Seofox.ir Seofox.ir Seofox.ir Seofox.ir Seofox.ir Seofox.ir Seofox.ir Seofox.ir Seofox.ir Seofox.ir Seofox.ir Seofox.ir Seofox.ir Seofox.ir Seofox.ir Seofox.ir Seofox.ir Seofox.ir Seofox.ir Seofox.ir Seofox.ir Seofox.ir Seofox.ir Seofox.ir Seofox.ir Seofox.ir Seofox.ir Seofox.ir Seofox.ir Seofox.ir Seofox.ir Seofox.ir Seofox.ir Seofox.ir Seofox.ir Seofox.ir Seofox.ir Seofox.ir Seofox.ir Seofox.ir Seofox.ir Seofox.ir Seofox.ir Seofox.ir Seofox.ir Seofox.ir Seofox.ir Seofox.ir Seofox.ir Seofox.ir Seofox.ir Seofox.ir Seofox.ir Seofox.ir Seofox.ir Seofox.ir Seofox.ir Seofox.ir Seofox.ir Seofox.ir Seofox.ir Seofox.ir Seofox.ir Seofox.ir Seofox.ir Seofox.ir Seofox.ir Seofox.ir Seofox.ir Seofox.ir Seofox.ir Seofox.ir Seofox.ir Seofox.ir Seofox.ir Seofox.ir Seofox.ir Seofox.ir Seofox.ir Seofox.ir Seofox.ir Seofox.ir Seofox.ir Seofox.ir Seofox.ir Seofox.ir Seofox.ir Seofox.ir Seofox.ir Seofox.ir Seofox.ir Seofox.ir Seofox.ir Seofox.ir Seofox.ir Seofox.ir Seofox.ir Seofox.ir Seofox.ir Seofox.ir Seofox.ir Seofox.ir Seofox.ir Seofox.ir Seofox.ir Seofox.ir Seofox.ir Seofox.ir Seofox.ir Seofox.ir Seofox.ir Seofox.ir Seofox.ir Seofox.ir Seofox.ir Seofox.ir Seofox.ir Seofox.ir Seofox.ir Seofox.ir Seofox.ir Seofox.ir Seofox.ir Seofox.ir Seofox.ir Seofox.ir Seofox.ir Seofox.ir Seofox.ir Seofox.ir Seofox.ir Seofox.ir Seofox.ir Seofox.ir Seofox.ir Seofox.ir Seofox.ir Seofox.ir Seofox.ir Seofox.ir Seofox.ir Seofox.ir Seofox.ir Seofox.ir Seofox.ir Seofox.ir Seofox.ir Seofox.ir Seofox.ir Seofox.ir Seofox.ir Seofox.ir Seofox.ir Seofox.ir Seofox.ir Seofox.ir Seofox.ir Seofox.ir Seofox.ir Seofox.ir Seofox.ir Seofox.ir Seofox.ir Seofox.ir Seofox.ir Seofox.ir Seofox.ir Seofox.ir Seofox.ir Seofox.ir Seofox.ir Seofox.ir Seofox.ir Seofox.ir Seofox.ir Seofox.ir Seofox.ir Seofox.ir Seofox.ir Seofox.ir Seofox.ir Seofox.ir Seofox.ir Seofox.ir Seofox.ir Seofox.ir Seofox.ir Seofox.ir Seofox.ir Seofox.ir Seofox.ir Seofox.ir Seofox.ir Seofox.ir Seofox.ir Seofox.ir Seofox.ir Seofox.ir Seofox.ir Seofox.ir Seofox.ir Seofox.ir Seofox.ir Seofox.ir Seofox.ir Seofox.ir Seofox.ir Seofox.ir Seofox.ir Seofox.ir Seofox.ir Seofox.ir Seofox.ir Seofox.ir Seofox.ir Seofox.ir Seofox.ir Seofox.ir Seofox.ir Seofox.ir Seofox.ir Seofox.ir Seofox.ir Seofox.ir Seofox.ir Seofox.ir Seofox.ir Seofox.ir Seofox.ir Seofox.ir Seofox.ir Seofox.ir Seofox.ir Seofox.ir Seofox.ir Seofox.ir Seofox.ir Seofox.ir Seofox.ir Seofox.ir Seofox.ir Seofox.ir Seofox.ir Seofox.ir Seofox.ir Seofox.ir Seofox.ir Seofox.ir Seofox.ir Seofox.ir Seofox.ir Seofox.ir Seofox.ir Seofox.ir Seofox.ir Seofox.ir Seofox.ir Seofox.ir Seofox.ir Seofox.ir Seofox.ir Seofox.ir Seofox.ir Seofox.ir Seofox.ir Seofox.ir Seofox.ir Seofox.ir Seofox.ir Seofox.ir Seofox.ir Seofox.ir Seofox.ir Seofox.ir Seofox.ir Seofox.ir Seofox.ir Seofox.ir Seofox.ir Seofox.ir Seofox.ir Seofox.ir Seofox.ir Seofox.ir Seofox.ir Seofox.ir Seofox.ir Seofox.ir Seofox.ir Seofox.ir Seofox.ir Seofox.ir Seofox.ir Seofox.ir Seofox.ir Seofox.ir Seofox.ir Seofox.ir Seofox.ir Seofox.ir Seofox.ir Seofox.ir Seofox.ir Seofox.ir Seofox.ir Seofox.ir Seofox.ir Seofox.ir Seofox.ir Seofox.ir Seofox.ir Seofox.ir Seofox.ir Seofox.ir Seofox.ir Seofox.ir Seofox.ir Seofox.ir Seofox.ir Seofox.ir Seofox.ir Seofox.ir Seofox.ir Seofox.ir Seofox.ir Seofox.ir Seofox.ir Seofox.ir Seofox.ir Seofox.ir Seofox.ir Seofox.ir Seofox.ir Seofox.ir Seofox.ir Seofox.ir Seofox.ir Seofox.ir Seofox.ir Seofox.ir Seofox.ir Seofox.ir Seofox.ir Seofox.ir Seofox.ir Seofox.ir Seofox.ir Seofox.ir Seofox.ir Seofox.ir Seofox.ir Seofox.ir Seofox.ir Seofox.ir Seofox.ir Seofox.ir Seofox.ir Seofox.ir Seofox.ir Seofox.ir Seofox.ir Seofox.ir Seofox.ir Seofox.ir Seofox.ir Seofox.ir Seofox.ir Seofox.ir Seofox.ir Seofox.ir Seofox.ir Seofox.ir Seofox.ir Seofox.ir Seofox.ir Seofox.ir Seofox.ir Seofox.ir Seofox.ir Seofox.ir Seofox.ir Seofox.ir Seofox.ir Seofox.ir Seofox.ir Seofox.ir Seofox.ir Seofox.ir Seofox.ir Seofox.ir Seofox.ir Seofox.ir Seofox.ir Seofox.ir Seofox.ir Seofox.ir Seofox.ir Seofox.ir Seofox.ir Seofox.ir Seofox.ir Seofox.ir Seofox.ir Seofox.ir Seofox.ir
seofox · 43 weeks and 2 days ago
Pug Puppies for Sale Near Me pugs puppies for sale teacup pugs for sale pug puppies for sale by owner pug puppies ohio PUG PUPPY FOR SALE NEAR ME PUG PUPPIES FOR SALE pug puppies for sale in kentucky Pug Puppies for Sale Under $500 Near Me pug puppies for sale in texas pug puppies for sale $200 pugs for sale near me under $500 pugs for sale under $400 near me pugs for sale near me puppies for sale near me under $500 pug puppies for sale under $1,000 near me pug for sale pug puppies for sale under $300 Brindle Pug Pitbull Pug Mix Pugs for sale cheap Cheap pug affordable pug puppies for sale near me black pugs for sale near me White Pugs for sale pug dog for sale free pug puppies pug puppies for sale in my area mn pug breeders pug puppies indiana pugs for sale michigan PUG PUPPY ADOPTION Pug puppies for sale Pug puppies for sale near me Pug puppies near me Pug Puppies for Sale Under $500 Near Me Cute Pug Puppies Black pug puppies Black pug puppies for sale pug puppies for adoption black pug puppies for sale near me chihuahua pug mix puppies how much is a pug puppy teacup pug puppies baby pug puppies pictures of pug puppies pug puppies for sale in Ohio pug puppies price pug mix puppies teacup pug puppies for sale best food for pug puppy newborn pug puppies pug puppies craigslist pug puppies for sale craigslist adorable pug puppies how much does a pug puppy cost Pitbull pug mix puppies pug pit mix puppy pug puppies for sale $200 pug puppies for sale in NJ Pug puppies for sale in Wisconsin pug puppy cost pug puppy food royal canin pug puppy royal canin pug puppy food fawn pug puppy pug puppies for sale florida pug puppies for sale in Indiana pug puppies for sale in KY pug puppies for sale in NC pug dog puppy AKC Registered Pug Puppies For sale cheap pug puppies for sale near me cheap pug puppies for sale in California cheap pug puppies for sale in nj Black Pug Puppies for sale pugs puppies for sale pug puppies indiana Amazing! This blog looks just like my old one! It's on a completely different subject but it has pretty much the same layout and design. Wonderful choice of colors!
rahimhh21 · 14 weeks ago
Pug Puppies for Sale Near Me pugs puppies for sale teacup pugs for sale pug puppies for sale by owner pug puppies ohio PUG PUPPY FOR SALE NEAR ME PUG PUPPIES FOR SALE pug puppies for sale in kentucky Pug Puppies for Sale Under $500 Near Me pug puppies for sale in texas pug puppies for sale $200 pugs for sale near me under $500 pugs for sale under $400 near me pugs for sale near me puppies for sale near me under $500 pug puppies for sale under $1,000 near me pug for sale pug puppies for sale under $300 Brindle Pug Pitbull Pug Mix Pugs for sale cheap Cheap pug affordable pug puppies for sale near me black pugs for sale near me White Pugs for sale pug dog for sale free pug puppies pug puppies for sale in my area mn pug breeders pug puppies indiana pugs for sale michigan PUG PUPPY ADOPTION Pug puppies for sale Pug puppies for sale near me Pug puppies near me Pug Puppies for Sale Under $500 Near Me USA USA USA USA USA USA Cute Pug Puppies Black pug puppies Black pug puppies for sale pug puppies for adoption black pug puppies for sale near me chihuahua pug mix puppies how much is a pug puppy teacup pug puppies baby pug puppies baby pug puppies for sale pictures of pug puppies pug puppies for sale in Ohio pug puppies price pug mix puppies teacup pug puppies for sale best food for pug puppy newborn pug puppies pug puppies craigslist pug puppies for sale craigslist adorable pug puppies how much does a pug puppy cost Pitbull pug mix puppies pug pit mix puppy pug puppies for sale $200 pug puppies for sale in NJ Pug puppies for sale in Wisconsin pug puppy cost pug puppy food royal canin pug puppy royal canin pug puppy food fawn pug puppy pug puppies for sale florida pug puppies for sale in Indiana pug puppies for sale in KY pug puppies for sale in NC pug dog puppy AKC Registered Pug Puppies For sale cheap pug puppies for sale near me cheap pug puppies for sale in California cheap pug puppies for sale in nj Black Pug Puppies for sale pugs puppies for sale
Perfecthomepugs · 5 weeks and 3 days ago

What do you think?

Any thoughts on this command? Does it work on your machine? Can you do the same thing with only 14 characters?

You must be signed in to comment.

What's this?

commandlinefu.com is the place to record those command-line gems that you return to again and again. That way others can gain from your CLI wisdom and you from theirs too. All commands can be commented on, discussed and voted up or down.

Share Your Commands



Stay in the loop…

Follow the Tweets.

Every new command is wrapped in a tweet and posted to Twitter. Following the stream is a great way of staying abreast of the latest commands. For the more discerning, there are Twitter accounts for commands that get a minimum of 3 and 10 votes - that way only the great commands get tweeted.

» http://twitter.com/commandlinefu
» http://twitter.com/commandlinefu3
» http://twitter.com/commandlinefu10

Subscribe to the feeds.

Use your favourite RSS aggregator to stay in touch with the latest commands. There are feeds mirroring the 3 Twitter streams as well as for virtually every other subset (users, tags, functions,…):

Subscribe to the feed for: