Bash比较浮点数

Question

I have an array:

pole_registru=("3" "8" "3.2" "6" "1" "3" "1.3" "3.3" "5.8" "12" "0" "3")

I need find elements in the array which are lower than 1 (including number with floating points) and count them (number of lower elements save to variable A ).

I try:

for i in "${pole_registru[@]}"
do
  Hodnota="Value of actual: $i"
  compare=`echo "$i" | bc`
  echo --$compare--
  if [ $i < 1 ]; then (( A+=1 )); else (( A=A )); fi
  echo "$Value ($x) ($A)"
  sleep 1
done

Issue into console:

./kontrolaNul.sh: řádek 33: 1: Folder or file does not.

Answer 1

Use bc directly to compare the numbers, like this

pole_registru=("3" "8" "3.2" "6" "1" "3" "1.3" "3.3" "5.8" "12" "0" "3")
for i in "${pole_registru[@]}"
do
  Hodnota="Value of actual: $i"
  if (( $(bc <<< "$i<1") )) ; then (( A+=1 )); else (( A=A )); fi
  echo "$Value ($i) ($A)"
  sleep 1
done

The double parentheses construct is used to evaluate the string output of bc as a numerical value. (I also changed $x to $i in the echo line)

That gives:

$ . t.sh 
 (3) (1)
 (8) (1)
 (3.2) (1)
 (6) (1)
 (1) (1)
 (3) (1)
 (1.3) (1)
 (3.3) (1)
 (5.8) (1)
 (12) (1)
 (0) (2)
 (3) (2)

Answer 2

This should solve your problem:

for i in "${pole_registru[@]}"
do
  Hodnota="Value of actual: $i"
  compare=`echo "$i" | bc`
  echo --$compare--
  if [ `echo "$i < 1" | bc` -eq 1 ]; then (( A+=1 )); else (( A=A )); fi
  echo "$Value ($x) ($A)"
  sleep 1
done

Answer 3

Your immediate problem is that you're using < in your expression, which is the input file redirection operator - it's complaining because you have no file called 1 to get input from.

If you change that to -lt , it will fix that problem.

However, I don't think the bash numerics cater for floating point so you'll probably have more trouble after that.

One way to get around that limitation is to use an external tool that does do floating point, use it to subtract one from your test number, then use the bash regular expression matching to detect a negative number:

if [[ $(echo $i - 1 | BC_LINE_LENGTH=0 bc) =~ - ]] ; ...

The bc program is used to calculate x - 1 for your given x , don't worry about the BC_LINE_LENGTH setting, that's just to prevent line wrapping within bc ).

Then, if the result starts with a - character, the result was obviously less than zero (because x was less than one).