{"id":6731,"date":"2016-01-10T21:17:03","date_gmt":"2016-01-10T20:17:03","guid":{"rendered":"https:\/\/www.dbi-services.com\/blog\/linux-how-to-check-the-exit-status-of-several-piped-commands\/"},"modified":"2016-01-10T21:17:03","modified_gmt":"2016-01-10T20:17:03","slug":"linux-how-to-check-the-exit-status-of-several-piped-commands","status":"publish","type":"post","link":"https:\/\/www.dbi-services.com\/blog\/linux-how-to-check-the-exit-status-of-several-piped-commands\/","title":{"rendered":"Linux – How to check the exit status of several piped commands"},"content":{"rendered":"

As piping in bash commands is common and very usefull, controling the exit status of each piped commands in bash scripting can be vital, especially for backups.<\/p>\n

\n
\n
\n
\n
I was checking by a customer the backups of a critical MySQL instance and was surprised even stunned that the return status of all of them was always\u00a0 successfull when tested but physically on disk, the dumps were all empty.<\/div>\n
No valid backups since a long time meaning no possible recovery.<\/div>\n
Oups! How can it be?<\/div>\n<\/div>\n
I immediately opened the backup script with “vi” and had a look to the used statement which was the following:<\/div>\n
\n
mysqldump -u $USERNAME -p $PASS $DBNAME | bzip2 -9c -c > Dump.sql.gz<\/pre>\n
Now, what if the backup failed and the bzip2 command succeeded?\nIn fact, the exit status will be the one of the last command.<\/pre>\n
echo $? \n0<\/pre>\n
And this will be always successfull.<\/p>\n<\/div>\n
So, the\u00a0 solution to check the exit status of a particular command in piped commands is to use an inbuilt linux variable called\u00a0 PIPESTATUS.<\/div>\n
PIPESTATUS is an array variable which contain the exit status of every piped commands.<\/div>\n
In our case,<\/div>\n
echo ${PIPESTATUS[0]} will refer to the backup\u00a0 and will be greater than 0 if it fails
\necho ${PIPESTATUS[1]} will refer to the compression<\/div>\n
echo ${PIPESTATUS[*]} or echo ${PIPESTATUS[@]} will give you the status of both.<\/div>\n
\n
\n
So, one solution in our example could be:<\/pre>\n
mysqldump -u $USERNAME -p $PASS $DBNAME | bzip2 -9c -c > Dump.sql.gz\n\nif [ ${PIPESTATUS[0]} -ne \"0\" ]\nthen\n    echo \"the MySQL Database backup failed with Error: ${PIPESTATUS[0]}\";\nelse\n    echo \"The MySQL Database backup was successfull!\";\nfi<\/pre>\n
I hope it will help...<\/pre>\n<\/div>\n<\/div>\n<\/div>\n<\/div>\n<\/div>\n","protected":false},"excerpt":{"rendered":"
As piping in bash commands is common and very usefull, controling the exit status of each piped commands in bash scripting can be vital, especially for backups. I was checking by a customer the backups of a critical MySQL instance and was surprised even stunned that the return status of all of them was always\u00a0 […]<\/p>\n","protected":false},"author":28,"featured_media":6732,"comment_status":"open","ping_status":"open","sticky":false,"template":"","format":"standard","meta":{"_acf_changed":false,"footnotes":""},"categories":[42],"tags":[46],"type_dbi":[],"class_list":["post-6731","post","type-post","status-publish","format-standard","has-post-thumbnail","hentry","category-operating-systems","tag-linux-unix"],"acf":[],"yoast_head":"\nLinux - How to check the exit status of several piped commands - dbi Blog<\/title>\n<meta name=\"description\" content=\"Blog about Linux command: PIPESTATUS\" \/>\n<meta name=\"robots\" content=\"index, follow, max-snippet:-1, max-image-preview:large, max-video-preview:-1\" \/>\n<link rel=\"canonical\" href=\"https:\/\/www.dbi-services.com\/blog\/linux-how-to-check-the-exit-status-of-several-piped-commands\/\" \/>\n<meta property=\"og:locale\" content=\"en_US\" \/>\n<meta property=\"og:type\" content=\"article\" \/>\n<meta property=\"og:title\" content=\"Linux - 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