shell 中的浮点比较

Question

Can you please suggest to me the syntax for doing floating point comparison in a Bash script? I would ideally like to use it as part of an if statement. Here is a small code snippet:

key1="12.3"
result="12.2"

if (( $result <= $key1 ))
then
    # some code here
fi

Answer 1

bc is your friend:

key1="12.3"
result="12.2"
if [ $(bc <<< "$result <= $key1") -eq 1 ]
    then
    # some code here
fi

Note the somewhat obscure here string ( <<< ) notation, as a nice alternative to echo "$result <= $key1" | bc echo "$result <= $key1" | bc .

Also, the un-bash-like bc prints 1 for true and 0 for false .

Answer 2

bash doesn't do floats, use awk

key1=12.3
result=12.5
var=$(awk 'BEGIN{ print "'$key1'"<"'$result'" }')    
# or var=$(awk -v key=$key1 -v result=$result 'BEGIN{print result<key?1:0}')
# or var=$(awk 'BEGIN{print "'$result'"<"'$key1'"?1:0}')
# or 
if [ "$var" -eq 1 ];then
  echo "do something"
else
  echo "result more than key"
fi

there are other shells that can do floats, like zsh or ksh, you might like to try using them as well

Answer 3

使用 bc 的另一个简单明了的方法是：

if ((`bc <<< "10.21>12.22"`)); then echo "true"; else echo "false"; fi

Answer 4

Using the exit() function of awk makes it almost readable.

key1=12.3
result=12.5

# the ! awk is because the logic in boolean tests 
# is the opposite of the one in shell exit code tests
if ! awk "{ exit ($result <= $key1) }" < /dev/null
then
        # some code here
fi

Note that there is not need to reuse the [ operator as if already uses the exit value.

Answer 5

### The funny thing about bash is this:
> AA=10.3
> BB=10.4
### It needs `$` for compare
> [[ $AA > $BB ]] && echo Hello
> [[ $AA < $BB ]] && echo Hello
Hello

Yeah, I know it's cheating but it works. And scientific notation does not work here.

Answer 6

yu can use this awk comparison inside a if clause, it will print 1 (true) if the condition is true else 0 (false), and those values will be interpreted as boolean vals by the if

if (( $(awk 'BEGIN {print ("'$result'" <= "'$key1'")}') )); then
    echo "true"
else
    echo "false"
fi

Answer 7

I was using bc until now, I found in some distros there was not bc installed, and I did not want to go through sudo apt install bc but python was there. Using python:

  if python -c "import sys; sys.exit(0 if float($float_1) > float($float_2) else 1)"; 
    then
    echo "true"
         else
           echo "false"
  fi