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: >=20 > On 05/11/2015 15:37, Devin Teske wrote: >>=20 >>> On May 11, 2015, at 12:18 PM, Brooks Davis <brooks@freebsd.org = <mailto:brooks@freebsd.org>> wrote: >>>=20 >>> On Sun, May 10, 2015 at 03:45:48PM -0400, John Baldwin wrote: >>>>=20 >>>>> On May 8, 2015, at 19:36, Xin LI <delphij@FreeBSD.org = <mailto:delphij@FreeBSD.org>> wrote: >>>>>=20 >>>>> Author: delphij >>>>> Date: Fri May 8 23:36:31 2015 >>>>> New Revision: 282672 >>>>> URL: https://svnweb.freebsd.org/changeset/base/282672 >>>>>=20 >>>>> Log: >>>>> Always convert uuid to lower case. >>>>>=20 >>>>> MFC after: 2 weeks >>>>>=20 >>>>> Modified: >>>>> head/etc/rc.d/hostid >>>>>=20 >>>>> Modified: head/etc/rc.d/hostid >>>>> = =3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D= =3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D= =3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D= =3D=3D=3D >>>>> --- 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() >>>>>=20 >>>>> valid_hostid() >>>>> { >>>>> - uuid=3D$1 >>>>> + uuid=3D$(echo $1 | tr '[:upper:]' '[:lower:]') >>>>=20 >>>> tr is in /usr/bin so this breaks systems with a separate /usr. = Perhaps you could use dd with conv=3Dlcase instead? >>>=20 >>> Alterntively, a shell function "ltr" exists in rc.subr for this = purpose. >>>=20 >>=20 >> ltr would not work in this situation, for multiple reasons. >>=20 >> 1. ltr doesn=E2=80=99t support character classes >> 2. ltr is for replacing one or more characters (cannot be a class) = with a single string (of variable length, 0+). >>=20 >> In /etc/networks.subr you can see an example usage of ltr: >>=20 >> 287 = <https://svnweb.freebsd.org/base/head/etc/network.subr?view=3Dmarkup#l287>= _punct=3D".-/+" >> 288 = <https://svnweb.freebsd.org/base/head/etc/network.subr?view=3Dmarkup#l288>= ltr ${_if} "${_punct}" '_' _if >>=20 >>=20 >> 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 = =E2=80=9C_if=E2=80=9D (over- >> writing previous contents which may have contained aforementioned >> characters replaced with underscore). >>=20 >> An attempt to use ltr in the below fashion: >>=20 >> ltr $string =E2=80=98[:lower:]=E2=80=99 =E2=80=98[:upper:]=E2=80=99 = somevar >>=20 >> would surely fail. >>=20 >> While it is indeed *possible* to write a find/replace function in = native- >> shell that supports character classes, it would not be a small = function. >> The primary issue is that you need to know what the character that >> matched the class and there aren=E2=80=99t any built-ins that provide = this info. >>=20 >> For example: >>=20 >> case =E2=80=9C$src=E2=80=9D in *[[:lower:]]*) >>=20 >> will trigger when you have a lower-case character that needs = conversion >> to upper-case (or opposite if using *[[:upper:]]*) BUT you won=E2=80=99= t know >> what the character was that you matched (so how can you know which >> upper-case character to supplant)? >>=20 >> The function will have to resort to complicated substring mechanics = or >> any other seldom known procedure. >>=20 >> I=E2=80=99ll have a noodle on it and see what I can come up with. = It=E2=80=99s 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 =E2=80=94 coming up with a solution that embraces the use = of the >> character class I would believe to be more efficient). >=20 > John Baldwin suggested "dd conv=3Dlcase", since dd is in /bin. >=20 > $ echo MixedCaseLetters | dd conv=3Dlcase 2>/dev/null > mixedcaseletters >=20 > $ type dd > dd is /bin/dd >=20 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=E2=80=99t 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 =E2=80=94 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=E2=80=99s still probably likely that the dd approach is the best = (unless you=E2=80=99re doing it repetitively in a tight loop ;D). =E2=80=94=20 Devin
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