cannot add fractions in loop using bc in a script?

sonu kumar · 02-11-2010, 12:03 AM

hi dear all

i have tried a lot to add floating values in while loop using bc, but no sucess!!!

script is :

read a1
read a11

b=$(echo "scale=10; $a1/1000" | bc)
c=$b
echo "c is $c"

while [[ $a1 -lt $a11 ]] ; do
c=$(echo "scale=10; $c+0.005" | bc) #
echo "c is $c"
done

output:
....
....
c is 12.7000000000
c is 12.7050000000
...
.....infinite loop?

with regards!!!
skumar

catkin · 02-11-2010, 12:42 AM

$a1 and $a11 are not changed in the loop so the [[ $a1 -lt $a11 ]] test will always return the same result.

David the H. · 02-11-2010, 12:42 AM

First of all, please use [code][/code] tags around your code, to preserve formatting and readability.

Second, your while loop doesn't do anything to change the test.

Code:

while [[ $a1 -lt $a11 ]] ; do

     c=$(echo "scale=10; $c+0.005" | bc)

     echo "c is $c"

done

If a1 is less than a11, the loop will continue indefinitely.

chrism01 · 02-11-2010, 01:08 AM

Your problem is that bash only does integer comparisons (even though bc can do float calcs); the usual trick for langs like that is simply to multiply (scale) your actual values up enough to be able to treat them as integer eg if you want increments of 0.1, multiply by 10 and use increments of 1.
You could just use a better lang eg Perl.

sonu kumar · 02-11-2010, 07:42 AM

Quote:

Originally Posted by chrism01

Your problem is that bash only does integer comparisons (even though bc can do float calcs); the usual trick for langs like that is simply to multiply (scale) your actual values up enough to be able to treat them as integer eg if you want increments of 0.1, multiply by 10 and use increments of 1.
You could just use a better lang eg Perl.

hi chris !!

can you tell/suggest me the good and simple links to learn the perl language.

thanks in advance!!!
Sk

chrism01 · 02-11-2010, 05:24 PM

http://perldoc.perl.org/ - lang definition with loads of examples & extra tutorials
http://www.perlmonks.org/?node=Tutorials - more tutorials

Enjoy