How can I compare floating number in a shell script?

abefroman · 06-24-2005, 11:24 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, 12:02 PM

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, 01:20 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, 01:36 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, 01:54 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, 02:26 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, 02:37 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, 05:54 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, 10:48 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, 07:25 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, 01:20 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, 05:28 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, 08:53 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