CODEWITHSUNDEEP
linuxbash
Dinesh Subedi
Dinesh Subedi

Reputation: 2663

Strange behaviour while multiplying negative number with -1

Iam doing scripting using bash where I get the negative number like this

-001 , -002 , -003 , ........................., -008 , -009 , -010 , -011 , -012 .....

I have to change them to positive number so I decided to multiply -1 with them. Then

$ val=$(( -1*-001 ))
$ echo $val
$ 1
$ val=$(( -1*-002 ))
$ echo $val
$ 2

Result are fine up to number -007 but when I multiply with -008 and -009 then error occur as below

$ val=$(( -1*-008 ))
bash: -1*-008: value too great for base (error token is "008")

$ val=$(( -1*-009 ))
bash: -1*-009: value too great for base (error token is "009")

Another strange behaviour is that when I multiply with -010, -011 ,-012 and so on... unusual result occur like below 

$ val=$(( -1*-010 ))
$ echo $val
$ 8
$ val=$(( -1*-011 ))
$ echo $val
$ 9
$ val=$(( -1*-012 ))
$ echo $val
$ 10
$ val=$(( -1*-013 ))
$ echo $val
$ 11

and so on............

Why this happens?

Upvotes: 2

Views: 1472

Answers (2)

svante
svante

Reputation: 1385

You can force decimal (instead of octal) values with 10# prefix :

$ val=$(( -1*-10#008 ))
$ echo $val
8

Upvotes: 6

user229044
user229044

Reputation: 239382

Leading zeros denote numbers in octal. 010 and 10 are not the same number; the first is octal: 010 octal is 8 in decimal. Similarly, "009" isn't a real number, hence the error you're seeing: there is no digit "9" in octal.

You need to strip leading zeros.

Upvotes: 8

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