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Comparing Negative #'s in IF Statements

 
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# 1  
Old 10-17-2008
Comparing Negative #'s in IF Statements
Hi,

I am writing a BASH shell script. I would like to construct an IF statement that allows me to determine if a variable is between -180 and 180. Example:

if [ $WEST -lt -180.0 -o $WEST -gt 180.0 ]; then
echo 'WEST NOT WITHIN BOUNDS'
fi

However, I believe the negative sign is causing errors. What is the proper BASH syntax to make this tyoe of comparison? Thanks a lot.

Mike
# 2  
Old 10-17-2008
Hammer & Screwdriver Check on your brackets
See the following:
(I set coord1 and coord2 as variables earlier.)

Code:
> valuex=13
> echo $valuex $coord1 $coord2 ;if [ $valuex -lt $coord1 ] || [ $valuex -gt $coord2 ]; then echo "*** out of bounds ***"; fi
13 -180 180

> valuex=-181
> echo $valuex $coord1 $coord2 ;if [ $valuex -lt $coord1 ] || [ $valuex -gt $coord2 ]; then echo "*** out of bounds ***"; fi
-181 -180 180
*** out of bounds ***

> valuex=181
> echo $valuex $coord1 $coord2 ;if [ $valuex -lt $coord1 ] || [ $valuex -gt $coord2 ]; then echo "*** out of bounds ***"; fi
181 -180 180
*** out of bounds ***
>

# 3  
Old 10-17-2008
Hi,

Please correct me if I am wrong, but it seems that your solution is too simply define the bounds first, and then use those variables in the IF statement. I got that to work for me. But it doesn't seem to accept the comparison of decimals. Is that true on your end?

Also is that "check your brackets" directed at me?

Thanks again.
# 4  
Old 10-17-2008
Hammer & Screwdriver
I did not check for decimals. I think the decimal will cause a problem since the -gt or -lt is expecting integers.

I only worked on you comment about negatives.

My comment about brackets was in the writing of the or statement.
You had [ this -o that ]
I had [ this ] || [that ]
# 5  
Old 10-17-2008
Ah, yes I have seen both ways of doing an OR statement. Any ideas on how I can compare negative integers AND decimals?

Thanks
Mike
# 6  
Old 10-17-2008
Hammer & Screwdriver This can be cleaned up some
Because of the issue where unix by default only wants to do integer math, the following works for decimals greater than 0. Need to think about logic to fix when a negative number -- must subtract one. (Can be done, just tired this afternoon!)

Essentially, was experimenting with using cut to break up the value into pieces.

Maybe this can get you thinking about an approach to the matter.


Code:
#! /usr/bin/bash

value1=182.1
pre=`echo $value1 | cut -d"." -f1`
dec=`echo $value1 | cut -d"." -f2`
echo $pre $dec

if [ `echo $value1 | cut -d"." -f2` -eq 0 ]
   then
     value2=`echo $value1 | cut -d"." -f1`
   else
     value2=`echo $value1 | cut -d"." -f1`
     value3=`echo $value2 + 1 | bc`
fi

if [ $value3 -lt -180 ] || [ $value3 -gt 180 ]
   then
   echo "Value is out of bounds"
fi

# 7  
Old 10-17-2008
You have to use awk or perl or python... etc.
Code:
result=$(echo "$WEST" | awk ' ($1> -180.0 && $1 < 180.0)?$0="1":$0="0"')
if [ $result -eq 1 ]; then
   # success
else
   # failure
fi

 
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