Bash limiting precision of floating point variables

Question

In Ubuntu 14.04.1 LTS 64-bit bash I am declearing floating point variables by multiplying floating point bash variables in bc with scale set to 3; however, I cannot get the number of digits after the decimal point to be zero and get rid of the zero to the left of the decimal point. How can I transform, say 0.005000000 into .005? This is necessary due to my file naming convention. Thanks for your recommendations.

UPDATE: Can I use it for already defined shell variables and redefining them? The following code gives me an error.

~/Desktop/MEEP$ printf "%.3f\n" $w
bash: printf: 0.005000: invalid number
0,000

The output of locale

@vesnog:~$ locale
LANG=en_US.UTF-8
LANGUAGE=en_US
LC_CTYPE="en_US.UTF-8"
LC_NUMERIC=tr_TR.UTF-8
LC_TIME=tr_TR.UTF-8
LC_COLLATE="en_US.UTF-8"
LC_MONETARY=tr_TR.UTF-8
LC_MESSAGES="en_US.UTF-8"
LC_PAPER=tr_TR.UTF-8
LC_NAME=tr_TR.UTF-8
LC_ADDRESS=tr_TR.UTF-8
LC_TELEPHONE=tr_TR.UTF-8
LC_MEASUREMENT=tr_TR.UTF-8
LC_IDENTIFICATION=tr_TR.UTF-8
LC_ALL=

The output of echo $w

@vesnog:~$ echo $w
0.005000

Answer 1

A simple way is to use printf:

$ printf "%.3f\n" 0.005000000000
0.005

To remove the leading 0, just parse it out with sed:

$ printf "%.3f\n" 0.005000000000 | sed 's/^0//'
.005

Answer 2

There is a special variable called scale. You can set this variable to limit the precision.

EXAMPLE

$ echo "300/7" | bc -l
42.85714285714285714285

To limit the precision,

$ echo "scale=2; 300/7" | bc -l
42.85

UPDATED

$ echo "scale=3; 300/7" | bc -l | sed 's/[0-9]*\././g'
.857

Answer 3

This sed command removes trailing zeros:

sed 's/\(0\.0*[1-9][1-9]*\)0*/\1/'

It remembers any values beginning with 0., followed by zero or more 0's, followed by 1 or more digits from 1-9, followed by zero or more 0's. It then truncates the zero or more trailing 0's.

This allows you to parse out an arbitrary number of trailing zeros, and retain any arbitrarily low number greater than zero. regardless of how small it is.

For example

0.054000 becomes 0.054, or 0.00000010000000 becomes 0.0000001, and so on.

For more info check out Grymoires awesome sed tutorial.

Answer 4

I know I'm late but for any new people who google this problem. Invalid number hasn't been solved from the OP in the most voted answer, in fact the answer also gives me an invalid number error.

Reason is LC_NUMERIC variable from locale. Simple solution: use "," instead of "." as a decimal point. Also simple, change the locale variable.

Test it

export LC_NUMERIC="en_US.UTF-8"

Permanent

echo 'export LC_NUMERIC="en_US.UTF-8"' >>~/.bashrc

Answer 5

Why not grep?

echo "$your_number" | grep -o '.*[1-9]'