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Magd
Asked: 2012-03-30 12:10:24 +0800 CST

simple nagios script failing

  • 772

What is wrong with the following if-then-else? I never can hit the else.

if [ $result > $value ]; then
   echo HEALTH: OK.  Result is $result  Value is $value
   exit 0
 else
   echo HEALTH: CRITICAL.  Result is $result which is over $value
   exit 2
 fi


# ./check_cw_auto <AWS variables> 5.0
HEALTH: OK. Result is 275593.8 Value is 5.0

# ./check_cw_auto <AWS variables> 10000000.0
HEALTH: OK. Result is 275593.8 Value is 10000000.0

I'm trying to create a nagios bash script. I did try -gt instead of >, but that give an error. Example:

./check_cw_auto <AWS variables> 5.0 
./check_cw_auto: line 30: [: 256497.2: integer expression expected
HEALTH: CRITICAL. Result is 256497.2 which is over 5.0
scripting bash nagios

3 Answers

  1. In [], two strings are compared lexicographically, not numerically. You want to use -gt or -lt.

    Edit: In response to your update, bash does not have floating point logic. You need to use whole numbers.

    • 4

  2. As you have a floating point number as part of the comparison you can use bc to do the comparison, bc returns 1 if the comparison is true

    if [ $(echo "$result > $value" | bc -q ) -eq 1 ]; then
   echo HEALTH: OK.  Result is $result  Value is $value
   exit 0
 else
   echo HEALTH: CRITICAL.  Result is $result which is over $value
   exit 2
 fi
    • 4

  3. http://mywiki.wooledge.org/BashPitfalls#A.5B.5B_.24foo_.3E_7_.5D.5D

    It's being treated as a string comparison.

    Use "-gt" instead:

    if [ $result -gt $value ]; then
    • 0