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Editorial Team
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Asked: 2026-05-30T15:06:38+00:00

I am trying to write a simple Bash script to monitor MySQL replication status.

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I am trying to write a simple Bash script to monitor MySQL replication status. The script is like this:

#!/bin/bash
dbhost=192.168.1.2
repluser=root
replpasswd=password
echo "show slave status\G"|\
mysql -h $dbhost -u $repluser -p$replpasswd > tmpd 2>/dev/null
repl_IO=$(cat tmpd | grep "Slave_IO_Running" | cut -f2 -d':')
repl_SQL=$(cat tmpd | grep "Slave_SQL_Running" | cut -f2 -d':')
if [ $repl_IO != "Yes" -o $repl_SQL != "Yes" ] ; then
     echo
     echo -e "\033[31m Replication Error."
     echo -e "\033[0m"
     mail -s "replication error" email@domain.com < tmpd

else
     echo
     echo -e "\033[32mReplication is working fine"
     echo -e "\033[0m"

fi

The problem is that the script only works if both the master and the slave are up. If the master is down, and I run the script, it displays the error message and sends the email.
If both master/slave are up, the script displays “Replication is working fine” which is okay. But when I shutdown the slave and run the script, I get this error:

./monitor.bash: line 9: [: too many arguments

Replication is working fine

I know the problem is that since I’m querying the slave MySQL server, it’s not finding it. So it’s not checking the conditions Slave_IO_Running and Slave_SQL_Running. How would I go
about checking if the slave server is up BEFORE running those conditions. So in short, I only want “Replication is working fine” to be displayed, if both the master & slave are up and
running and it matches those conditions. Any help would be appreciated. Thank you.

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1 Answer

  1. Editorial Team

    If $repl_IO and $repl_SQL are blank, then this:

    if [ $repl_IO != "Yes" -o $repl_SQL != "Yes" ] ; then

    is equivalent to this:

    if [ != Yes -o != Yes ] ; then

    and I think you can see why that doesn’t work. You need either to wrap your parameter-expansions in double-quotes, so that they’re treated as single arguments no matter what they contain:

    if [ "$repl_IO" != "Yes" -o "$repl_SQL" != "Yes" ] ; then

    or to use [[...]] instead of [...], since it’s a bit smarter with these things:

    if [[ $repl_IO != "Yes" -o $repl_SQL != "Yes" ]] ; then

    or both:

    if [[ "$repl_IO" != "Yes" -o "$repl_SQL" != "Yes" ]] ; then
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