The other day I’ve been puzzled by the results of a cron job script. \u00a0The bash script in question was written in a hurry a while back, and I was under the assumption that if any of its steps fail, the whole script will fail. \u00a0I was wrong. \u00a0Some commands were failing, but the script execution continued. \u00a0It was especially difficult to notice, due to a number of unset variables, piped commands, and redirected error output.<\/p>\n
Once I realized the problem, I got even more puzzled as to what was the best solution. \u00a0Sure, you can check an exit code after each command in the script, but that didn’t seem elegant of efficient.<\/p>\n
A quick couple of Google searches brought me to this StackOverflow thread<\/a> (no surprise there), which opened my eyes on a few bash options that can be set at the beginning of the script to stop execution when an error or warning occurs (similar to use strict; use warnings;<\/em> in Perl). \u00a0Here’s the test script for you with some test commands, pipes, error redirects, and options to control all that.<\/p>\n Save it to test.sh, make executable (chmod +x test.sh), and run like so:<\/p>\n Then try to comment out some options and some commands to see what happens in different scenarios.<\/p>\n I think, from now on, those three options will be the standard way I start all of my bash scripts.<\/p>\n <\/p>\n\n","protected":false},"excerpt":{"rendered":"\n The other day I’ve been puzzled by the results of a cron job script. \u00a0The bash script in question was written in a hurry a while back, and I was under the assumption that if any of its steps fail, the whole script will fail. \u00a0I was wrong. \u00a0Some commands were failing, but the script … Continue reading Bulletproof Bash : Stop script on error<\/span><\/a><\/p>\n\n","protected":false},"author":2,"featured_media":0,"comment_status":"open","ping_status":"open","sticky":false,"template":"","format":"standard","meta":{"_monsterinsights_skip_tracking":false,"_monsterinsights_sitenote_active":false,"_monsterinsights_sitenote_note":"","_monsterinsights_sitenote_category":0,"_jetpack_newsletter_access":"","_jetpack_dont_email_post_to_subs":false,"_jetpack_newsletter_tier_id":0,"_jetpack_memberships_contains_paywalled_content":false,"_jetpack_feature_clip_id":0,"_jetpack_memberships_contains_paid_content":false,"footnotes":"","jetpack_publicize_message":"Bulletproof Bash : Stop script on error #SysAdmin #programming #bash #CLI #Linux","jetpack_publicize_feature_enabled":true,"jetpack_social_post_already_shared":true,"jetpack_social_options":{"image_generator_settings":{"template":"highway","default_image_id":0,"font":"","enabled":false},"version":2},"jetpack_post_was_ever_published":false,"_links_to":"","_links_to_target":""},"categories":[1,6,18,133,62],"tags":[3098,1960],"keyring_services":[],"class_list":["post-27447","post","type-post","status-publish","format-standard","hentry","category-general","category-linux","category-programming","category-sysadmin","category-technology","tag-bash","tag-command-line"],"aioseo_notices":[],"aioseo_head":"\n\t\t\n\t\n\t\n\t\n\t\n\t\n\t\n\t\t\n\t\t\n\t\t\n\t\t\n\t\t\n\t\t\n\t\t\n\t\t\n\t\t\n\t\t\n\t\t\n\t\t\n\t\t\n\t\t\n\t\t\n\t\t\n\t\t\n\t\t\n\t\t\n\t\t\r\n#!\/bin\/bash\r\n\r\n# Stop on error\r\nset -e\r\n# Stop on unitialized variables\r\nset -u\r\n# Stop on failed pipes\r\nset -o pipefail\r\n\r\n# Good command\r\necho "We start here ..."\r\n\r\n# Use of non-initialized variable\r\necho "$FOOBAR"\r\necho "Still going after uninitialized variable ..."\r\n\r\n# Bad command with no STDERR\r\ncd \/foobar 2> \/dev\/null\r\necho "Still going after a bad command ..."\r\n\r\n# Good command into a bad pipe with no STDERR\r\necho "Good" | \/some\/bad\/script 2> \/dev\/null\r\necho "Still going after a bad pipe ..."\r\n\r\n# Benchmark\r\necho "We should never get here!"\r\n<\/pre>\n
\r\n$ .\/test.sh || echo Something went wrong\r\n<\/pre>\n