Date: Mon, 11 May 2015 12:49:58 -0700 From: Devin Teske <dteske@FreeBSD.org> To: Eric van Gyzen <vangyzen@FreeBSD.org> Cc: Brooks Davis <brooks@freebsd.org>, 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: <5AE2B9A2-FF6E-422A-B2E2-7E6CA85999BD@FreeBSD.org> In-Reply-To: <555106B5.3010104@FreeBSD.org> References: <201505082336.t48NaWRS080408@svn.freebsd.org> <C072FED2-FBED-4EF9-9D74-11B485594AD7@FreeBSD.org> <20150511191850.GC68045@spindle.one-eyed-alien.net> <9FB76653-EF89-48E5-B4E8-A2006923B76A@FreeBSD.org> <555106B5.3010104@FreeBSD.org>
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> On May 11, 2015, at 12:44 PM, Eric van Gyzen <vangyzen@FreeBSD.org> wrote: > > On 05/11/2015 15:37, Devin Teske wrote: >> >>> On May 11, 2015, at 12:18 PM, Brooks Davis <brooks@freebsd.org <mailto: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 <mailto: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). > > 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 > Yeah, I have to say, this looks by far the simplest approach. Even if I or Colin or someone else were to whip up a comprehensive native shell function that does this, I can’t say that it would be chosen necessarily over the dd approach (which itself is comprehensive but may suffer the lag of pulling dd into memory — most significant when say, running off of CD). Not knowing where the code is destined nor how many times iteratively it could be passed over in a casual day, it’s still probably likely that the dd approach is the best (unless you’re doing it repetitively in a tight loop ;D). — Devin
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