Linux – How to check the exit status of several piped commands

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  successfull when tested but physically on disk, the dumps were all empty.
No valid backups since a long time meaning no possible recovery.
Oups! How can it be?
I immediately opened the backup script with “vi” and had a look to the used statement which was the following:
1
mysqldump -u $USERNAME -p $PASS $DBNAME | bzip2 -9c -c > Dump.sql.gz
Now, what if the backup failed and the bzip2 command succeeded?
In fact, the exit status will be the one of the last command.
1
2
echo $?
0

And this will be always successfull.

So, the  solution to check the exit status of a particular command in piped commands is to use an inbuilt linux variable called  PIPESTATUS.
PIPESTATUS is an array variable which contain the exit status of every piped commands.
In our case,
echo ${PIPESTATUS[0]} will refer to the backup  and will be greater than 0 if it fails
echo ${PIPESTATUS[1]} will refer to the compression
echo ${PIPESTATUS[*]} or echo ${PIPESTATUS[@]} will give you the status of both.
So, one solution in our example could be:
1
2
3
4
5
6
7
8
mysqldump -u $USERNAME -p $PASS $DBNAME | bzip2 -9c -c > Dump.sql.gz
 
if [ ${PIPESTATUS[0]} -ne "0" ]
then
    echo "the MySQL Database backup failed with Error: ${PIPESTATUS[0]}";
else
    echo "The MySQL Database backup was successfull!";
fi
0 (0)
Article Rating (No Votes)
Rate this article
Attachments
There are no attachments for this article.
Comments
There are no comments for this article. Be the first to post a comment.
Full Name
Email Address
Security Code Security Code
Related Articles RSS Feed
logrotate Log Rotate Configuration
Viewed 2811 times since Sun, Jan 12, 2020
RHEL : How to deal with “CLOSE_WAIT” and “TIME_WAIT” connection
Viewed 23937 times since Thu, Feb 14, 2019
LVM: Extend an existing Logical Volume / Filesystem
Viewed 2060 times since Sat, Jun 2, 2018
Increase A VMware Disk Size (VMDK) Formatted As Linux LVM without rebooting
Viewed 14846 times since Wed, May 30, 2018
Linux - Cannot login from remote console but can access via ssh
Viewed 4041 times since Fri, Jun 8, 2018
Migrate a Linux System from Red Hat Enterprise to CentOS
Viewed 9778 times since Fri, May 15, 2020
RHCS: Configure an active/backup pacemaker cluster
Viewed 8480 times since Sun, Jun 3, 2018
ZFS: Grow/Shrink an existing zfs filesystem
Viewed 5575 times since Sun, Jun 3, 2018
Linux 16 Useful Bandwidth Monitoring Tools to Analyze Network Usage in Linux
Viewed 11143 times since Mon, Sep 21, 2020
bash mistakes This page is a compilation of common mistakes made by bash users. Each example is flawed in some way.
Viewed 8591 times since Sun, Dec 6, 2020