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Re: Number with sign is read as octal despite a leading 10#


From: Ilkka Virta
Subject: Re: Number with sign is read as octal despite a leading 10#
Date: Tue, 10 Jul 2018 13:44:07 +0300
User-agent: Mozilla/5.0 (Macintosh; Intel Mac OS X 10.11; rv:52.0) Gecko/20100101 Thunderbird/52.9.0

I think the problematic case here is when the number comes as input from some program, which might or might not print a leading sign or leading zeroes, but when we know that the number is, in any case, decimal.

E.g. 'date' prints leading zeroes, which is easy enough to handle:

hour=$(date +%H)

hour=${hour#0}         # remove one leading zero, or
hour="10#$hour"        # make it base-10

The latter works even with more than one leading zero, but neither works with a sign. So, handling numbers like '-00159' gets a bit annoying:

$ num='-00159'
$ num="${num:0:1}10#${num:1}"; echo $(( num + 1 ))
-158

And that's without checking that the sign was there in the first place.


Something like that will probably not be too common, but an easier way to force any number to be interpreted in base-10 (regardless of leading zeroes) could be useful. If there is a way, I'd be happy to hear.


On 10.7. 04:37, Clint Hepner wrote:
The + is a unary operator, not part of the literal. Write $((+10#0034)) instead.

--
Clint
On Jul 9, 2018, 9:24 PM -0400, Isaac Marcos <address@hidden>, wrote:
Configuration Information [Automatically generated, do not change]:
Machine: x86_64
OS: linux-gnu
Compiler: gcc
Compilation CFLAGS: -DPROGRAM='bash' -DCONF_HOSTTYPE='x86_64'
-DCONF_OSTYPE='linux-gnu' -DCONF_MACHTYPE='x86_64-pc-linux-gnu'
-DCONF_VENDOR
uname output: Linux IO 4.9.0-6-amd64 #1 SMP Debian 4.9.88-1+deb9u1
(2018-05-07) x86_64 GNU/Linux
Machine Type: x86_64-pc-linux-gnu

Bash Version: 4.4
Patch Level: 12
Release Status: release

Description:
A value inside an arithmetic expansion is processed as octal despite using
a 10# preffix.

Repeat-By:
$ echo $((10#+0034))
28

Fix:
Extract optional sign before parsing the number, re-attach after.

--
Cases are always threesome:
Best case, Worst case, and Just in case


--
Ilkka Virta / address@hidden



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