mysql returning 0 when should return 1 in BASH script

Question

I am working on a bash script to dump a database to a file to be uploaded via FTP. It will be launched by a cron job and the sql server isn't localhost.

I have the script working but am running into a road block with error checking. If the script cant connect to the sql server (in the unlikely event that it goes down) I want it to stop and output whatever the problem was to an error log. The outputting to error log works fine, but the script still runs and creates a blank file. I am trying to use the $? to check if the mysql connection failed and even when I am using a testing server that is off, a 0 is returned instead of a 1. I'm wearing a hole in the wall that I am bashing my head against, what am I doing wrong?

If this has been asked before, please point me in the right direction but I couldn't find any answers when I searched.

contents of the bash script:

{  
mysql -h $HOST -u $USERNAME -p$PASSWORD < dump.sql | sed "s/\t/\",\"/g;s/^/\"/;s/$/\"/" > test.csv  
} 2>error.log  
if [ $? -ne 0 ]; then { echo "SQL Server connection failed. Aborting" ; exit 1; } fi

$? is capturing the return value from sed I guess, not mysql, look here: stackoverflow.com/questions/1221833/… — guido
– guido, Commented Dec 5, 2015 at 23:09
or you can do mysql ... < dump.sql > test.csv 2>err ; mySqlStat=$? ; sed '....' test.csv .Good luck. — shellter
– shellter, Commented Dec 5, 2015 at 23:12

Bruce P · Accepted Answer · 2015-12-05 23:13:50Z

1

$? in this case is returning the result of your sed command, not the mysql command. Since the sed command is always succeeding (you're passing valid input to it and a valid set of substitutions) you're always going to get 0 in $?.

When using one or more piped commands in a bash script then you want to use the built-in PIPESTATUS variable which will let you examine the return value of each command in a series of piped commands, no matter how many you pipe together.

answered Dec 5, 2015 at 23:13

Bruce P

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2 Comments

Lucas Over a year ago

This fixed it. Just want to also point out (for other.. "special" people like me) PIPESTATUS may not work if you are using "sh <script>" which I was. You need to chmod +x the script and run "./ <script>". This was why my previous forays into PIPESTATUS were not working as what info I found assumed you had chmod'ed already.

4ae1e1 Over a year ago

Instead of inspecting PIPESTATUS, pipefail is an option that's almost always beneficial and causes no harm.

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