svn commit: r282672 - head/etc/rc.d

[Eric van Gyzen]

On 05/11/2015 15:37, Devin Teske wrote:
> 
>> On May 11, 2015, at 12:18 PM, Brooks Davis <brooks at freebsd.org <mailto:brooks at freebsd.org>> wrote:
>>
>> On Sun, May 10, 2015 at 03:45:48PM -0400, John Baldwin wrote:
>>>
>>>> On May 8, 2015, at 19:36, Xin LI <delphij at FreeBSD.org <mailto:delphij at FreeBSD.org>> wrote:
>>>>
>>>> Author: delphij
>>>> Date: Fri May  8 23:36:31 2015
>>>> New Revision: 282672
>>>> URL: https://svnweb.freebsd.org/changeset/base/282672
>>>>
>>>> Log:
>>>> Always convert uuid to lower case.
>>>>
>>>> MFC after:    2 weeks
>>>>
>>>> Modified:
>>>> head/etc/rc.d/hostid
>>>>
>>>> Modified: head/etc/rc.d/hostid
>>>> ==============================================================================
>>>> --- head/etc/rc.d/hostid    Fri May  8 23:29:42 2015    (r282671)
>>>> +++ head/etc/rc.d/hostid    Fri May  8 23:36:31 2015    (r282672)
>>>> @@ -58,7 +58,7 @@ hostid_set()
>>>>
>>>> valid_hostid()
>>>> {
>>>> -    uuid=$1
>>>> +    uuid=$(echo $1 | tr '[:upper:]' '[:lower:]')
>>>
>>> tr is in /usr/bin so this breaks systems with a separate /usr.  Perhaps you could use dd with conv=lcase instead?
>>
>> Alterntively, a shell function "ltr" exists in rc.subr for this purpose.
>>
> 
> ltr would not work in this situation, for multiple reasons.
> 
> 1. ltr doesn’t support character classes
> 2. ltr is for replacing one or more characters (cannot be a class) with a single string (of variable length, 0+).
> 
> In /etc/networks.subr you can see an example usage of ltr:
> 
> 287 <https://svnweb.freebsd.org/base/head/etc/network.subr?view=markup#l287>	_punct=".-/+"
> 288 <https://svnweb.freebsd.org/base/head/etc/network.subr?view=markup#l288>	ltr ${_if} "${_punct}" '_' _if
> 
> 
> The result of this is to take a value of (for example) foo.bar and replace
> any occurrences of period, minus, forward slash, or plus with instead
> a single underscore. The result is stuffed into the variable “_if” (over-
> writing previous contents which may have contained aforementioned
> characters replaced with underscore).
> 
> An attempt to use ltr in the below fashion:
> 
> ltr $string ‘[:lower:]’ ‘[:upper:]’ somevar
> 
> would surely fail.
> 
> While it is indeed *possible* to write a find/replace function in native-
> shell that supports character classes, it would not be a small function.
> The primary issue is that you need to know what the character that
> matched the class and there aren’t any built-ins that provide this info.
> 
> For example:
> 
> case “$src” in *[[:lower:]]*)
> 
> will trigger when you have a lower-case character that needs conversion
> to upper-case (or opposite if using *[[:upper:]]*) BUT you won’t know
> what the character was that you matched (so how can you know which
> upper-case character to supplant)?
> 
> The function will have to resort to complicated substring mechanics or
> any other seldom known procedure.
> 
> I’ll have a noodle on it and see what I can come up with. It’s not exactly
> immediately coming to me how to do this in any simple fashion while
> maintaining efficiency (read: by not iterating over every single character
> and also by not having a giant massive case statement with every letter
> spelled out — coming up with a solution that embraces the use of the
> character class I would believe to be more efficient).

John Baldwin suggested "dd conv=lcase", since dd is in /bin.

$ echo MixedCaseLetters | dd conv=lcase 2>/dev/null
mixedcaseletters

$ type dd
dd is /bin/dd

Eric