Error in Bash script arithmetic syntax

Question

Script:

#!/bin/bash
vpct=5.3 
echo $((vpct*15))

Error:

./abc.sh: line 5: 5.3: syntax error: invalid arithmetic operator (error token is ".3")

I know I don't need a script to multiply 5.3 * 15, but this small script to single out the error. Please advise.

SirDarius · Accepted Answer · 2011-02-18 11:47:15Z

8

According to http://www.softpanorama.org/Scripting/Shellorama/arithmetic_expressions.shtml:

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

You should use bc to perform such calculations, just as in dogbane's solution, except that you should escape the expression using quotes so the * character doesn't cause unwanted shell expansion.

echo "$vpct*15" | bc

answered Feb 18, 2011 at 11:47

SirDarius

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Comments

kurumi · Accepted Answer · 2011-02-18 13:58:28Z

3

Besides bc, there are other tools you can tools you can try

awk -v vpct="$VPCT" 'BEGIN{print vpct * 15}'

echo $vpct | ruby -e 'print gets.to_f * 15 '

echo  "$vpct 15 * p" | dc

answered Feb 18, 2011 at 13:58

kurumi

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1 Comment

nert Over a year ago

Since you are listing alternatives, if you use zsh instead of bash the script will simply work.

dogbane · Accepted Answer · 2011-02-18 11:48:53Z

3

You should use bc for floating point arithmetic:

echo "$vpct*15" | bc

edited Feb 18, 2011 at 11:48

answered Feb 18, 2011 at 11:43

dogbane

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Comments

Cedric · Accepted Answer · 2011-02-18 11:41:31Z

0

$(( $vpct * 15 )) // (add a $ sign should do it)

answered Feb 18, 2011 at 11:41

Cedric

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4 Comments

Cedric Over a year ago

--sorry I cannot try these solution, but will be happy if one of these works out for you :)

Humble Debugger Over a year ago

./abc.sh: line 5: 5.3*15 : syntax error: invalid arithmetic operator (error token is ".3*15 ") Neither work

Cedric Over a year ago

sorry Humble and dogbane - at least above is a link to the same problem

Dennis Williamson Over a year ago

Dollar signs aren't necessary in an arithmetic context in Bash.

user332325 · Accepted Answer · 2011-02-18 11:45:38Z

0

Shebang should be written like #! And anyway $(()) is only for integers.

answered Feb 18, 2011 at 11:45

user332325

Comments

Dennis Williamson · Accepted Answer · 2011-02-18 15:14:59Z

0

If you have ksh available, it will do float arithmetic.

answered Feb 18, 2011 at 15:14

Dennis Williamson

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