Question

I am trying to write a Bash script to run a MySQL query from a string constructed in the script. I have been able to construct the query string, and it looks correct when echo’d. And I can cut and paste it into the shell command line and it runs. But, I need to basically cut the query results to just the words, OK or CRITICAL. Nothing else. When I try to save the query result to a bash variable I get:

mysql: unknown option ‘-2’

If I cut out the grep and cut code, I get the mysql --help results. So, it’s not liking my mysql string, but I don’t know why. Help?

BTW- Running CentOS 6.3

alert=`mysql myDB -e "select value from config_table where name=\"ach_alert_time\"\G" | /bin/grep value: | /bin/cut -f2 -d:`
echo $alert  #Brings back 18,50,00

sql="mysql myDB -e 'select if(count(*) > 0,\"CRITICAL\",\"OK\") as STATUS from xyz_batch where timestamp > concat(date(now()),\" \",maketime("$alert"))\G' | /bin/grep OK  | /bin/cut -f2 -d:"
echo $sql # mysql myDB -e 'select if(count(*) > 0,"CRITICAL","OK") as STATUS from xyz_batch where timestamp > concat(date(now())," ",maketime( 18,50,00))\G' | /bin/grep OK | /bin/cut -f2 -d

status=`$sql`

# Whoops!
# mysql: unknown option '-2'

echo $status

Answer 1

The problem is that when you run $sql as a command, it under goes word-splitting, filename expansion, and so on, with no respect for any quotation-marks that $sql might contain. And it won’t handle pipes and other shell metacharacters. For example, if you’re in a directory that contains the files foo and bar, then this:

cmd="echo '     *     ' | grep baz"
$cmd

will print ' bar foo ' | grep baz — it won’t preserve whitespace, it will expand the * into a list of files, and it will treat | and grep as arguments to echo.

You can work around this by using the command eval "$sql" instead of just $sql:

status=`eval "$sql"`

but you may want to re-evaluate your design a bit. Maybe there’s a better way to achieve what you want?

---

Edited to add: You say that you’re constructing the query in the script, but do you actually need to store the entire command in a variable? Something like this:

sql="select if(count(*) > 0,\"CRITICAL\",\"OK\") as STATUS from xyz_batch where timestamp > concat(date(now()),\" \",maketime("$alert"))\G"
status=`mysql myDB -e "$sql" | /bin/grep OK  | /bin/cut -f2 -d:`

would not have this problem, since then $sql is then just a single argument, so you don’t need Bash to do anything special with it.