Roundtable February 2014

roundtable@muug.ca

18 participants
24 discussions

MUUG Meeting, Feb 11, 7:30pm -- Raspberry Pi Real Time Clock
by gedetil＠cs.umanitoba.ca 04 Feb '14

04 Feb '14

The Manitoba UNIX User Group (MUUG) will be holding its next monthly meeting on Tuesday, February 11. The meeting topic for this month is as follows: Raspberry Pi Real Time Clock Wyatt Zacharias will be presenting the Raspberry Pi along with a Real Time Clock circuit. "A real-time clock is a computer clock that keeps track of the current time. Although the term often refers to the devices in personal computers, servers and embedded systems, RTCs are present in almost … [View More]

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Re: [RndTbl] strange race condition on file entries
by Trevor Cordes 03 Feb '14

03 Feb '14

But after programming heavily in Perl for 22 years (!!!) I can safely say I pretty much have the quirks and syntax oddities nailed. This is the first time in a long time something like this one has bit me, and it's understandable because I rarely use the glob op. If you don't like all the weirdness, the beauty of Perl is you can instead just program it as though it was C without malloc. I like choice. -------- Original message -------- From: Sean Walberg <sean(a)ertw.com> Date:2014/… [View More]02/02 20:00 (GMT-06:00) To: Continuation of Round Table discussion <roundtable(a)muug.mb.ca> Subject: Re: [RndTbl] strange race condition on file entries While I will always manage my life by the three great virtues, I must thank you for reminding me why I gave up slinging Perl. DWIM and all the sigils drive a man to an early grave, or at least a lot of nights debugging. Sean On Sun, Feb 2, 2014 at 1:10 PM, Trevor Cordes <trevor(a)tecnopolis.ca> wrote: I forgot to post what *does* work. There are a few different ways. You can force the glob to return a list (hence no caching/iterating): if (!@{[<$prefix-*>]}) { That's sure ugly, but it makes sense. [] forces the <> to return list and turns it into an anon array-ref. @ then derefs. {} is required by the parser to make sense of it all. !@ then does its normal thing of meaning "if there are zero elements in this array". You could also force it to list by assigning to an array: if (!(@a=<$prefix-*>)) { But I hate using temp vars when we don't need to; when the results are throwaway. Strangely, using the normal "we want a list" syntax of just putting () around the expression doesn't work in this case. I'm not sure why: if (!(<$prefix-*>)) { # doesn't work Also strangely, while perl has a "scalar" function to force a scalar (non-list) result, it doesn't have a "list" or "array" function to force a list. The scalar docs say list isn't necessary as it's usually the default/implied or can be forced with (). Woops, looks like I found a corner case. Ya, I could have been certain everything worked in the first place by doing opendir and iterating through the results, like one would in C, but the whole purpose of using perl is to do as much as possible in as few characters and lines. Laziness is the #1 programmer virtue, according to L.Wall and R.Schwarz. _______________________________________________ Roundtable mailing list Roundtable(a)muug.mb.ca http://www.muug.mb.ca/mailman/listinfo/roundtable -- Sean Walberg <sean(a)ertw.com> http://ertw.com/ [View Less]

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CF/SD/MMC readers under Linux
by Adam Thompson 03 Feb '14

03 Feb '14

I've noticed that many USB card readers are non-functional under Linux; according to the kernel developers, it's because relatively few of them implement the USB removable block storage class (protocol) correctly. While there are lots of expensive card readers that work with Linux, finding cheap ones is challenging. I think, however, that I've found the ultimate *cheap* USB card reader that works with Linux: the "Tech-1 USB 2.0 CARD READER" at Dollarama. IIRC, it cost $2. You'll almost … [View More]

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strange race condition on file entries
by Trevor Cordes 03 Feb '14

03 Feb '14

I'm running into a strange race condition, that appears to me to be a Linux bug of some sort. I'm doing, perl pseudocode: system "process-file outputfileprefix" # does work and puts it in files named outputfileprefix-0, outputfileprefix-1, etc sleep 1; if (!<outputfileprefix-[0-9]*>) { warn "try #2\n"; sleep 2; if (!<outputfileprefix-[0-9]*>) { warn "try #3\n"; die; } } # do something on outputfile* For those that don't know <> is perl's glob op, which … [View More]

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Roundtable February 2014