Subject: Re: bug#19240: cut 8.22 adds newline

From: Eric Blake <[email-masked]>
Date: Thu, 04 Dec 2014 14:48:17 -0700

On 12/04/2014 01:39 PM, Paul Eggert wrote:
> On 12/04/2014 10:41 AM, John Kendall wrote:
>> echo "$FILE ===========================\c"| cut -c1-30
> 
> Since you're going to have to rewrite it anyway if you want it to be
> portable, I suggest doing it this way:
> 
> printf '%.30s' "$FILE ==========================="
> 
> as it's a lot more efficient anyway.

Be careful; the POSIX specification of '%.30s' does NOT work well with
multibyte characters; it is specified as:

http://pubs.opengroup.org/onlinepubs/9699919799/basedefs/V1_chap05.html#tag_05
"precision
    Gives the minimum number of digits to appear for the d, o, i, u, x,
or X conversion specifiers (the field is padded with leading zeros), the
number of digits to appear after the radix character for the e and f
conversion specifiers, the maximum number of significant digits for the
g conversion specifier; or the maximum number of bytes to be written
from a string in the s conversion specifier. The precision shall take
the form of a <period> ( '.' ) followed by a decimal digit string; a
null digit string is treated as zero."

which means that it CAN and WILL corrupt output if the number of bytes
written falls in the middle of a multi-byte character.

-- 
Eric Blake   eblake redhat com    +1-919-301-3266
Libvirt virtualization library http://libvirt.org