#!/bin/bash
q=$(bc <<< "scale=2;$p*100")
head -n$q numbers.txt > secondcoordinate.txt
That's just part of the script, but I think it's enough to clarify my intentions. p is a variable with just two decimals, so q should be an integer... Nevertheless, bc shows, for example, 10.00 instead of 10.
How can I solve this?
You can't do this with the obvious scale=0 because of the way that the scale is determined.
The documentation indirectly explains that dividing by one is sufficient to reset the output to match the value of scale, which defaults to zero:
expr1 / expr2 The result of the expression is the quotient of the two expressions. The scale of the result is the value of the variable scale.
p=12.34; echo "($p*100)" | bc
1234.00
p=12.34; echo "($p*100)/1" | bc
1234
If your version of bc does not handle this, pipe it through sed instead:
p=12.34; echo "($p*100)" | bc | sed -E -e 's!(\.[0-9]*[1-9])0*$!\1!' -e 's!(\.0*)$!!'
1234
This pair of REs will strip trailing zeros from the decimal part of a number. So 3.00 will reduce to 3, and 3.10 will reduce to 3.1, but 300 will remain unchanged.
Alternatively, use perl and dispense with bc in the first place:
p=12.34; perl -e '$p = shift; print $p * 100, "\n"' "$p"
you can use awk to calculate the values
bash-3.2$ p=0.01
bash-3.2$ q=$(awk -vp_val="$p" 'BEGIN{print p_val*100}')
bash-3.2$ echo $q
1
bash-3.2$ p=0.02
bash-3.2$ q=$(awk -vp_val="$p" 'BEGIN{print p_val*100}')
bash-3.2$ echo $q
2
bash-3.2$ p=0.022
bash-3.2$ q=$(awk -vp_val="$p" 'BEGIN{print p_val*100}')
bash-3.2$ echo $q
2.2
You have lots of options. bc has known behavior where scale=0 doesn't always do what you expect, but there are a lot of workarounds. Here are just a few.
Use printf to limit your output to integers.
$ printf "%g\n" $(echo '12.34 * 100' | bc)
1234
If you want to stick with bc scaling, you need to specify both a scale of zero and divide by 1 to reset the scale. This is known behavior, but I really can't explain the why of it.
$ echo '12.34 * 100 / 1' | scale=0 bc
1234
Just strip off the unwanted trailing characters.
$ echo '12.34 * 100' | bc | sed 's/\.00$//'
1234
Use a brace expansion to return the value before the decimal.
$ p='12.34'; q=$(bc <<< "scale=2; $p*100"); echo ${q%%.00}
1234
Here is a bash function to remove trailing zeroes.
remove_trailing_zeroes()
{
declare -n n="$1"
# Prepend a 0 if number starts with a dot.
if [[ $n =~ ^[.] ]]; then
n="0$n"
fi
# Remove trailing zeroes
while [[ $n =~ [.].*0$ ]]; do
n="${n%0}"
done
# Remove trailing dot if any
if [[ $n =~ [.]$ ]]; then
n="${n%.}"
fi
}
You can then use it like this for your case:
q=$(bc <<< "scale=2;$p*100")
remove_trailing_zeroes q
head -n$q numbers.txt > secondcoordinate.txt
