bash shell中的浮点比较
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Floating point comparison in shell
提问by Kiran
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 ifstatement. Here is a small code snippet :
您能否向我建议在 Bash 脚本中进行浮点比较的语法？理想情况下，我希望将其用作if声明的一部分。这是一个小代码片段：
key1="12.3"
result="12.2"
if (( $result <= $key1 ))
then
# some code here
fi
采纳答案by ghostdog74
bash doesn't do floats, use awk
bash 不做浮动，使用 awk
key1=12.3
result=12.5
var=$(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
还有其他 shell 可以做浮动，比如 zsh 或 ksh，你也可以尝试使用它们
回答by Chen Levy
bcis your friend:
bc是你的朋友：
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 <= $key1" | bc.
请注意这里有点晦涩的字符串( <<<) 表示法，它是echo "$result <= $key1" | bc.
Also, the un-bash-like bcprints 1for trueand 0for false.
此外，未bash类似的bc版画1为真和0为假。
回答by Aquarius Power
another simple clear way with bc is this:
使用 bc 的另一个简单明了的方法是：
if ((`bc <<< "10.21>12.22"`)); then echo "true"; else echo "false"; fi
回答by Steve Schnepp
Using the exit()function of awkmakes it almost readable.
使用 的exit()功能awk使其几乎可读。
key1=12.3
result=12.5
# the ! awk is because the logic in boolean tests
# is the opposite of the one in shell exit code tests
if ! awk "{ exit ($result <= $key1) }" < /dev/null
then
# some code here
fi
Note that there is not need to reuse the [operator as ifalready uses the exit value.
请注意，不需要重用[运算符，因为if已经使用了退出值。
回答by linuxaos
### The funny thing about bash is this:
> AA=10.3
> BB=10.4
### It needs `$` 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.
是的，我知道这是作弊，但它有效。科学记数法在这里不起作用。
回答by ungalcrys
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
你可以在 if 子句中使用这个 awk 比较，如果条件为真，它将打印 1（真）否则 0（假），并且这些值将被 if 解释为布尔值
if (( $(awk 'BEGIN {print ("'$result'" <= "'$key1'")}') )); then
echo "true"
else
echo "false"
fi
回答by Rakib Fiha
I was using bc until now, I found in some distros there was not bc installed, and I did not want to go through sudo apt install bcbut python was there. Using python:
直到现在我一直在使用 bc，我发现在一些发行版中没有安装 bc，我不想通过sudo apt install bc但 python 就在那里。使用蟒蛇：
if python -c "import sys; sys.exit(0 if float($float_1) > float($float_2) else 1)";
then
echo "true"
else
echo "false"
fi
