Can somebody explain to me why a number with a leading 0 gives this funny behaviour?
#!/bin/bash
NUM=016
SUM=$((NUM + 1))
echo "$NUM + 1 = $SUM"
Will print:
016 + 1 = 15
60
128
The misunderstanding is that the numbers don't mean what you expect.
A leading zero denotes a number with base 8. I.e. 016 is the same as 8#16. If you want to keep the leading zero then you need 10#016.
> num=016
> echo $((num))
14
> echo $((10#$num))
16
answered Jan 8 '15 at 15:29
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23There are 10 types of people in the world. Those who understand binary, those who don't, those who weren't expecting a base 8 joke, and 5 other types of people. – Jon Story Jan 12 '15 at 13:36
42
Because:
~$ echo $((NUM))
14
if the number begins with 0, it is considered to be an octal value and 16 in octal is 14 in decimal.
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2That makes perfectly sence and explains why my script was overwriting my old files :-( – DeltaLima Jan 8 '15 at 15:33
printf "%03d\n" 10is completely usable in bash to obtain a leading zero for filenames and such. – Squeezy Jan 8 '15 at 19:15echo $((016))– Mehrdad Jan 9 '15 at 19:59