How can I compare floating number in a shell script?

abefroman · 06-24-2005, 10:24 AM

root@server1 [/]# ./ss3
./ss3: [: 3.1: integer expression expected
root@server1 [/]# cat ss3
#!/bin/bash
X=3.1
Y=3.2
empty_string=""
if [ $X -lt $Y ] # is $X less than $Y ?
then
echo "\$X=${X}, which is greater than \$Y=${Y}"
fi

Why does it say integer expression expected? How can I compare floats?

===========================================
It wont even work in C shell
root@server1 [/]# ./ss3
if: Badly formed number.
root@server1 [/]# cat ss3
#! /bin/csh -f
set X=3.1
set Y=4.1
if ( $X < $Y ) then
echo "\$X=${X}, which is greater than \$Y=${Y}"
endif

MoneyCat · 06-24-2005, 11:02 AM

Quote:

Why does it say integer expression expected? How can I compare floats?

This is because the -lt, -gt, -le, -ge, comparisons are only designed for integers. Try using these operators: >, <, >=, <=

Also there is a minor logic problem:

Code:

if [ $X -lt $Y ] # is $X less than $Y ?
then
echo "\$X=${X}, which is greater than \$Y=${Y}"

In the above code, you test if X is LESS THAN Y but then output X is GREATER THAN Y.

Good luck

abefroman · 06-24-2005, 12:20 PM

It still wont work, got any tips?

root@server1 [/]# cat ss3
#! /bin/csh -f
set X=3.1
set Y=4.1
if [ $X < $Y ] then
echo "wassup"
endif

root@server1 [/]# ./ss3
4.1: No such file or directory.
root@server1 [/]# pico ss3
root@server1 [/]# ./ss3
if: Badly formed number.
root@server1 [/]# cat ss3
#! /bin/csh -f
set X=3.1
set Y=4.1
if ( "$X" < "$Y" ) then
echo "wassup"
endif

abefroman · 06-24-2005, 12:36 PM

I tried it in perl but it doesnt store the right value to $a as it does in bash or cshell:
root@server1 [/]# cat ss4
#!/usr/bin/perl
$a=`uptime | awk -F'[, ]*' '{print $11}'`;
#echo "a = $a"
if ( $a > 5.2 ){
print $a;
}

root@server1 [/]# ./ss4
12:34pm up 29 days, 18:11, 1 user, load average: 0.43, 0.32, 0.33

MoneyCat · 06-24-2005, 12:54 PM

This code below works:

Code:

      1 #!/bin/bash
      2 X=3.1
      3 Y=3.2
      4 empty_string=""
      5
      6 if [ $X < $Y ] # is $X less than $Y ?
      7 then
      8     echo "\$X=${X}, which is less than \$Y=${Y}"
      9 elif [ $X > $y ]
     10 then
     11     echo "\$X=${X}, which is greater than \$Y=${Y}"
     12 fi

perfect_circle · 06-24-2005, 01:26 PM

Quote:

Originally posted by abefroman
root@server1 [/]# ./ss3
./ss3: [: 3.1: integer expression expected
root@server1 [/]# cat ss3
#!/bin/bash
X=3.1
Y=3.2
empty_string=""
if [ $X -lt $Y ] # is $X less than $Y ?
then
echo "\$X=${X}, which is greater than \$Y=${Y}"
fi

Why does it say integer expression expected? How can I compare floats?

===========================================
It wont even work in C shell
root@server1 [/]# ./ss3
if: Badly formed number.
root@server1 [/]# cat ss3
#! /bin/csh -f

set X=3.1
set Y=4.1
if ( $X < $Y ) then
echo "\$X=${X}, which is greater than \$Y=${Y}"
endif

As other people have already posted there are ways to work this out but in general case you should know this:

Quote:

Bash does not understand floating point arithmetic. It treats numbers containing a decimal point as strings.

Quote:

When not to use shell scripts

*

Resource-intensive tasks, especially where speed is a factor (sorting, hashing, etc.)
*

Procedures involving heavy-duty math operations, especially floating point arithmetic, arbitrary precision calculations, or complex numbers (use C++ or FORTRAN instead)
*

Cross-platform portability required (use C instead)
*

Complex applications, where structured programming is a necessity (need type-checking of variables, function prototypes, etc.)
*

Mission-critical applications upon which you are betting the ranch, or the future of the company
*

Situations where security is important, where you need to guarantee the integrity of your system and protect against intrusion, cracking, and vandalism
*

Project consists of subcomponents with interlocking dependencies
*

Extensive file operations required (Bash is limited to serial file access, and that only in a particularly clumsy and inefficient line-by-line fashion)
*

Need multi-dimensional arrays
*

Need data structures, such as linked lists or trees
*

Need to generate or manipulate graphics or GUIs
*

Need direct access to system hardware
*

Need port or socket I/O
*

Need to use libraries or interface with legacy code
*

Proprietary, closed-source applications (shell scripts put the source code right out in the open for all the world to see)

sirclif · 06-24-2005, 01:37 PM

yea, you can't do very much arithmetic in bash directly. you can pipe some commands to the calculator 'bc', and it will spit out the answer to the standard output.

> echo 3.14 + 5.16 | bc
8.30

as for a comparison, bc has some comparison capability, but you may be able to do something similar with a different tool, by piping it the comparison, and looking at what it returns.

ahh · 06-24-2005, 04:54 PM

I think awk will do the job:-

Code:

ahh@desktop ~ $ x=3.1; y=3.2; echo "$x $y" | awk '{if ($1 > $2) print $1; else print $2}'
3.2

I'm sure you can adapt it to your script.

wmjosiah · 08-07-2007, 09:48 AM

Actually, that doesn't work exactly. Even if you set X to 3.5, it will still say that X is less than Y.

Quote:

Originally Posted by MoneyCat

This code below works:

Code:

      1 #!/bin/bash
      2 X=3.1
      3 Y=3.2
      4 empty_string=""
      5
      6 if [ $X < $Y ] # is $X less than $Y ?
      7 then
      8     echo "\$X=${X}, which is less than \$Y=${Y}"
      9 elif [ $X > $y ]
     10 then
     11     echo "\$X=${X}, which is greater than \$Y=${Y}"
     12 fi

chrism01 · 08-07-2007, 06:25 PM

Another option in shell is to call expr for doing fp calcs.
I'm curious as to why you think Perl doesn't work, but then I noticed (commented out) 'echo', which is not a perl cmd/keyword.
Try
print "$a\n";

In fact, I'd just call uptime and then do the string parse in perl, instead of piping through awk.

makyo · 08-08-2007, 12:20 PM

Hi.

Some shells like zsh understand floating point. Here's a sample comparing bash and zsh. It writes a file t1, then asks bash and zsh to execute it:

Code:

#!/bin/sh

# @(#) s1       Compare bash and zsh for arithmetic.

set -o nounset

cat >t1 <<'EOF'

if [ -n "$BASH_VERSION" ]
then
  echo " From bash, version :$BASH_VERSION:"
elif [ -n "$ZSH_VERSION" ]
then
  echo " From zsh, version :$ZSH_VERSION:"
else
  echo " Unknown shell."
fi

float X Y
(( X = 3.0 + 0.5 ))
(( Y = 33.0 / 10.0 ))
if (( $X < $Y )) # is $X less than $Y ?
then
  echo "\$X=${X}, which is less than \$Y=${Y}"
elif (( $X > $Y ))
then
  echo "\$X=${X}, which is greater than \$Y=${Y}"
fi

EOF

echo
bash t1

echo
zsh t1

exit 0

Producing:

Code:

% ./s1

 From bash, version :2.05b.0(1)-release:
t1: line 12: float: command not found
t1: line 13: ((: X = 3.0 + 0.5 : syntax error in expression (error token is ".0+ 0.5 ")
t1: line 14: ((: Y = 33.0 / 10.0 : syntax error in expression (error token is ".0 / 10.0 ")
$X=3, which is less than $Y=33

 From zsh, version :4.2.4:
$X=3.500000000e+00, which is greater than $Y=3.300000000e+00

cheers, makyo

vamsi.coe · 09-12-2008, 04:28 AM

this is a naive way to do this.. but it works

#!/bin/ksh

parm_num=$#

if [ $parm_num -ne 2 ]
then
echo "enter two parameters"
exit 1
fi

d=`echo $1 - $2|bc`
#echo $d
count=`echo $d |grep "-" |wc -l`
if [ $count > 0 ]
then
echo "$2 is greater than $1"
else
echo "$1 is greater than $2"
fi

jchambers · 09-15-2008, 07:53 AM

EDIT: I deleted the prior function as it was flawed...

This one is more complex but will work wit numbers that are not the same length.

It checks if input A is greater that input B.

Code:

#!/bin/sh


a=2.25
b=1.0035

function f_AgtB()
{
	a=$1
	b=$2
	if [ "${a}" != "" -a "${b}" != "" ]
	then
		len_a=${#a}
		len_b=${#b}
		
		if [ $len_a -gt $len_b ]
		then
			b=${b}`f_add_zeros $(( $len_a - $len_b ))`
		else
			a=${a}`f_add_zeros $(( $len_b - $len_a ))`
		fi
		
		a=`echo $a | sed 's/\.//'`
		b=`echo $b | sed 's/\.//'`
		
		if [ $a -gt $b ]
		then
			echo 1
		else
			echo 0
		fi
	fi
}


function f_add_zeros()
{
	i=0
	while [ $i -lt $1 ]
	do
		out=${out}0
		((i++))
	done
	echo $out
}



if [ `f_AgtB $a $b` == 1 ]
then
	echo "CORRECT"
else
	echo "WRONG"
fi


exit

You may want to add some error correction if there is no '.'

Jon

ydrol · 03-26-2010, 04:41 AM

Just in case anyone is directed to this page, rather than doing some horribly convoluted solution, the following will work on most systems (even ones that dont have bc and perl) - eg many small devices running busybox.
As ahh said - 'awk' is probably your best friend here:

Code:

# Return the value of an operation
float_val() {
     echo | awk 'END { print '"$1"'; }'
}

Or more usefully

Code:

# Return status code of a comparison
float_test() {
     echo | awk 'END { exit ( !( '"$1"')); }'
}

Note you have to invert it as exit(0) = success.

Full Example:

Code:

$ cat q.sh
# Float comparison eg float '1.2 > 1.3'

# Return the value of an operation
float_val() {
     echo | awk 'END { print '"$1"'; }'
}

# Return status code of a comparison
float_test() {
     echo | awk 'END { exit ( !( '"$1"')); }'
}
##########################################

x=1.2
y=1.02
float_test "$x > $y" && echo "$x > $y"

float_test "$x < $y" && echo "$x < $y"

z=`float_val "$x + $y"`

echo "$x + $y = $z"

z=`float_val "$x - $y"`

echo "$x - $y = $z"

Output:

Code:

$ sh q.sh
1.2 > 1.02
1.2 + 1.02 = 2.22
1.2 - 1.02 = 0.18

Galogen · 04-26-2010, 04:11 AM

compare_result=`echo "2.2 > 1.1" | bc`
if [ $compare_result ]; then
echo 1
fi