Re: expr / (( )) different behavior
Hi,
Alessandro DE LAURENZIS wrote on Fri, Aug 11, 2017 at 01:14:48PM +0200:
> On Fri 11/08/2017 13:07, Janne Johansson wrote:
>> 0 is parsed as octal in places, so 09 would be bogus if octal.
> Thanks for the clarification; does that mean expr(1) can treat 10-base
> numbers only? No info in man page on this matter...
POSIX restricts expr(1) to handle decimal integers only and has some
complicated wording about which strings will be treated as integers
and which won't. I consider that too cumbersome to explain it in
the manual, in particular since it will rarely matter in practice.
But being specific about the number base adds precision and clarity
without harming readability.
OK?
Ingo
Index: expr.1
===
RCS file: /cvs/src/bin/expr/expr.1,v
retrieving revision 1.23
diff -u -p -r1.23 expr.1
--- expr.1 16 Jan 2015 15:30:10 - 1.23
+++ expr.1 11 Aug 2017 16:45:29 -
@@ -39,16 +39,17 @@ Returns the evaluation of
if neither expression evaluates to an empty string or zero;
otherwise, returns zero.
.It Ar expr1 Li "{=, >, >=, <, <=, !=}" Ar expr2
-Returns the results of integer comparison if both arguments are integers;
-otherwise, returns the results of string comparison using the locale-specific
-collation sequence.
+Returns the results of integer comparison if both arguments are
+decimal integers; otherwise, returns the results of string comparison
+using the locale-specific collation sequence.
The result of each comparison is 1 if the specified relation is true,
or 0 if the relation is false.
.It Ar expr1 Li "{+, -}" Ar expr2
-Returns the results of addition or subtraction of integer-valued arguments.
+Returns the results of addition or subtraction of decimal integer-valued
+arguments.
.It Ar expr1 Li "{*, /, %}" Ar expr2
Returns the results of multiplication, integer division, or remainder of
-integer-valued arguments.
+decimal integer-valued arguments.
.It Ar expr1 Li \&: Ar expr2
The
.Ql \&:
Re: expr / (( )) different behavior
2017-08-11 13:14 GMT+02:00 Alessandro DE LAURENZIS : > Hi Janne, > On Fri 11/08/2017 13:07, Janne Johansson wrote: > >> 0 is parsed as octal in places, so 09 would be bogus if octal. >> > [...] > > Thanks for the clarification; does that mean expr(1) can treat 10-base > numbers only? No info in man page on this matter... > Well, I think the default would be for simple math stuff to only use base 10. Then stuff like $(()) should perhaps say it accepts hex,octal or whatever outside of that. $ echo $(( 09 + 1)) ksh: 09 + 1: bad number `09' $ echo $(( 08 + 1)) ksh: 08 + 1: bad number `08' $ echo $(( 07 + 1)) 8 I have used the "skip leading zeros" at times with expr in order to handle possibly empty environment vars with stuff like: sleep $(expr 0$MIGHT_HAVE_VALUE + 1) so that an unset env-var will not make expr treat it like $(expr + 1) which would be an error. -- May the most significant bit of your life be positive.
Re: expr / (( )) different behavior
Hi Janne, On Fri 11/08/2017 13:07, Janne Johansson wrote: 0 is parsed as octal in places, so 09 would be bogus if octal. [...] Thanks for the clarification; does that mean expr(1) can treat 10-base numbers only? No info in man page on this matter... -- Alessandro DE LAURENZIS [mailto:jus...@atlantide.t28.net] LinkedIn: http://it.linkedin.com/in/delaurenzis
Re: expr / (( )) different behavior
0 is parsed as octal in places, so 09 would be bogus if octal. 2017-08-11 12:56 GMT+02:00 Alessandro DE LAURENZIS : > Dear misc@ readers, > > I was doing a little exercise with integer arithmetics and noticed the > following: > > [snip] > $ echo $(expr -09 % 3) > 0 > [snip] > > [snip] > $ echo $((-09 % 3)) > sh: -09 % 3: bad number `09' > [snip] > > bash seems to behave same way; just wondering if this inconsistency is > expected... > > -- > Alessandro DE LAURENZIS > [mailto:jus...@atlantide.t28.net] > LinkedIn: http://it.linkedin.com/in/delaurenzis > > -- May the most significant bit of your life be positive.
