Date: Mon, 11 May 2015 12:37:29 -0700 From: Devin Teske <dteske@FreeBSD.org> To: Brooks Davis <brooks@freebsd.org> Cc: John Baldwin <jhb@FreeBSD.org>, Xin LI <delphij@FreeBSD.org>, "src-committers@freebsd.org" <src-committers@freebsd.org>, "svn-src-all@freebsd.org" <svn-src-all@freebsd.org>, "svn-src-head@freebsd.org" <svn-src-head@freebsd.org>, Devin Teske <dteske@FreeBSD.org> Subject: Re: svn commit: r282672 - head/etc/rc.d Message-ID: <9FB76653-EF89-48E5-B4E8-A2006923B76A@FreeBSD.org> In-Reply-To: <20150511191850.GC68045@spindle.one-eyed-alien.net> References: <201505082336.t48NaWRS080408@svn.freebsd.org> <C072FED2-FBED-4EF9-9D74-11B485594AD7@FreeBSD.org> <20150511191850.GC68045@spindle.one-eyed-alien.net>
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> On May 11, 2015, at 12:18 PM, Brooks Davis <brooks@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@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). — Devin
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