Unix command for modulus

Ela1987 · 02-13-2014, 05:13 PM

HI,

Am trying to find the modulus using below two commands but i dont understand why the output differs. Can someone help me why there is difference and which one is correct command ?

1) mod=$((`expr ${INPUT_NUMBER} % 4`))
OUTPUT:
echo $mod
0[/COLOR]

2) mod=$(( $(INPUT_NUMBER} % 4 ))
OUTPUT:
echo $mod
2

rtmistler · 02-14-2014, 10:48 AM

Those both work, you have a typo in the second one. However it seems as if you're saying that the first doesn't work and the second one does.

Code:

$ INPUT_NUMBER=18
$ MOD=$((`expr ${INPUT_NUMBER} % 4`))
$ echo $MOD
2

$ MOD2=$(( ${INPUT_NUMBER} % 4 ))
$ echo $MOD2
2

Ela1987 · 02-14-2014, 11:15 AM

Sorry it was typo in my 2nd command, Can you try for the number 0272 as input number ? it should give different output.

colucix · 02-14-2014, 11:24 AM

The problem is that bash treats numbers with leading zeros as octal. You can still use the second command (without expr) but you have to force the shell to treat the number as decimal, e.g.

Code:

MOD2=$(( 10#${INPUT_NUMBER} % 4 ))

Ela1987 · 02-14-2014, 04:44 PM

Excellent answer, This whats i was looking for.