Wednesday, May 4, 2022

CC0 vs GPL

I've been writing little bits and pieces of my own code for many years now. And I've been releasing it as CC0 ("public domain"; see below). I've received a bit of criticism for it, and I guess I wanted to talk about it.

I like to write software. And I like it when other people benefit from my software. But I don't write end-user software, so the only people who benefit from my code are other programmers. But that's fine, I like a lot of programmers, so it's all good.

There are different ways I could offer my software. Much open-source software is available under a BSD license, an Apache license, or an MIT license. These differ in ways that are probably important to legal types, but for the most part, they mean that you can use the code for pretty much any purpose as long as you give proper attribution to the original source. So if I write a cool program and use some BSD code, I need to state my usage of that code somewhere in my program's documentation.

So maybe I should do that. After all, if I put in the effort to write the code, shouldn't I get the credit?

Yeah, that and a sawbuck will get me a cup of coffee. I don't think those attributions are worth much more than ego-boosting, and I guess my programmer ego doesn't need that boost.

With the exception of the GNU Public License (GPL), I don't think most open source ego-boosting licenses buy me anything that I particularly want. And they do introduce a barrier to people using my code. I've seen other people's code that I've wanted but decided not to use because of the attribution requirement. I don't want the attributions cluttering up my documentation, and adding licensing complications to anybody who wants to use my code. (For example, I was using somebody else's getopt module for a while, but realized I wasn't giving proper attribution, so I wrote my own.)

But what about GNU?

The GPL is a different beast. It is intended to be *restrictive*. It puts rules and requirements for the use of the code. It places obligations on the programmers. The stated goal of these restrictions is to promote freedom.

But I don't think that is really the point of GPL. I think the real point of GPL is to let certain programmers feel clean. These are programmers who believe that proprietary software is evil, and by extension, any programmer who supports proprietary software is also evil. So ignoring that I write proprietary software for a living, my CC0 software could provide a small measure of support for other proprietary software companies, making their jobs easier. And that makes me evil. Not Hitler-level evil, but at least a little bit evil.

If I license my code under GPLv3, it will provide the maximum protection possible for my open-source code to not support a proprietary system. And that might let me sleep better at night, knowing that I'm not evil.

Maybe somebody can tell me where I'm wrong on this. Besides letting programmers feel clean, what other benefit does GPL provide that other licenses (including CC0) don't?

I've read through Richard Stallman's "Why Open Source Misses the Point of Free Software" a few times, and he keeps coming back to ethics, the difference between right and wrong. Some quotes:

  • "The free software movement campaigns for freedom for the users of computing; it is a movement for freedom and justice."
  • "These freedoms are vitally important. They are essential, not just for the individual users' sake, but for society as a whole because they promote social solidarity—that is, sharing and cooperation."
  • "For the free software movement, free software is an ethical imperative..."
  • "For the free software movement, however, nonfree software is a social problem..."
I wonder what other things a free software advocate might believe. Is it evil to have secret recipes? Should Coke's secret formula be published? If I take a recipe that somebody puts on youtube and I make an improvement and use the modified recipe to make money, am I evil? What if I give attribution, saying that it was inspired by so-and-so's recipe, but I won't reveal my improvement? Still evil?

How about violin makers that have secret methods to get a good sound? Evil?

I am, by my nature, sympathetic to saying yes to all of those. I want the world to cooperate, not compete. I used to call myself a communist, believing that there should be no private property, and that we should live according to, "From each according to his ability, to each according to his needs". And I guess I still do believe that, in the same way that I believe we should put an end to war, cruelty, apathy, hatred, disease, hunger, and all the other social and cultural evils.

Oh, and entropy. We need to get rid of that too.

But none of them are possible, because ... physics? (That's a different subject for a different day.)

But maybe losing my youthful idealism is nothing to feel good about. Instead of throwing up my hands and saying it's impossible to do all those things, maybe I should pick one of them and do my best to improve the world. Perhaps the free software advocates have done exactly that. They can't take on all the social and cultural ills, so they picked one in which they could make a difference.

But free software? That's the one they decided was worth investing their altruism?

Free software advocates are always quick to point out that they don't mean "free" as in "zero cost". They are referring to freedoms - mostly the freedom to run a modified version of a program, which is a freedom that is meaningless to the vast majority of humanity. I would say that low-cost software is a much more powerful social good. GPL software promotes that, but so do the other popular open-source licenses. (And so does CC0).

So anyway, I guess I'm not a free software advocate (big surprise). I'll stick with CC0 for my code.

What is CC0

The CC0 license attempts to codify the concept of "public domain". The problem with just saying "public domain" is that the term does not have a universally agreed-upon definition, especially legally. So CC0 is designed to approximate what we think of as public domain.

Tuesday, February 15, 2022

Pathological cases

Jacob Kaplan-Moss said something wonderful yesterday:

Designing a human process around pathological cases leads to processes that are themselves pathological.

This really resonated with me.

Not much to add, just wanted to share.

Thursday, February 3, 2022

Nice catch, Grammarly

 I was writing an email and accidentally left out a word. I meant to write, "I've asked the team for blah...". But I accidentally omitted "asked", so it just said, "I've the team for blah...".

Grammarly flagged "I've", suggesting "I have". Since my brain still couldn't see my mistake, I thought it was complaining about "I've asked the team...". I was about to dismiss, but decided to click the "learn more" link. It said that, except in British English, using the contraction "I've" to express possession sounds unnatural or affected. As in: "Incorrect: I've a new car".

Ah HAH! That triggered me to notice the missing word "asked". I put it in, and Grammarly was happy. I consider this a good catch. Sure, it misdiagnosed the problem, but it knew it was a problem.

Thanks, Grammarly!


Wednesday, January 5, 2022

Bash Process Substitution

I generally don't like surprises. I'm not a surprise kind of guy. If you decide you don't like me and want to make me feel miserable, just throw me a surprise party.

But there is one kind of surprise that I REALLY like. It's learning something new ... the sort of thing that makes you say, "how did I not learn this years ago???"

Let's say you want the standard output of one command to serve as the input to another command. On day one, a Unix shell beginner might use file redirection:

$ ls >ls_output.tmp
$ grep myfile <ls_output.tmp
$ rm ls_output.tmp

On day two, they will learn about the pipe:

$ ls | grep myfile

This is more concise, doesn't leave garbage, and runs faster.

But what about cases where the second program doesn't take its input from STDIN? For example, let's say you have two directories with very similar lists of files, but you want to know if there are any files in one that aren't in the other.

$ ls -1 dir1 >dir1_output.tmp
$ ls -1 dir2 >dir2_output.tmp
$ diff dir1_ouptut.tmp dir2_output.tmp
$ rm dir[12]_output.tmp

So much for conciseness, garbage, and speed.

But, today I learned about Process Substitution:

$ diff <(ls -1 dir1) <(ls -1 dir2)

This basically creates two pipes, gives them names, and passes the pipe names as command-line parameters of the diff command. I HAVE WANTED THIS FOR DECADES!!!

And just for fun, let's see what those named pipes are named:

$ echo <(ls -l dir1) <(ls -1 dir2)
/dev/fd/63 /dev/fd/62

COOL!

(Note that echo doesn't actually read the pipes.)


VARIATION 1 - OUTPUT

The "cmda <(cmdb)" construct is for cmda getting its input from the output of cmdb. What about the other way around? I.e., what if cmda wants to write its output, not to STDOUT, but to a named file, and you want that output to be the standard input of cmdb? I'm having trouble thinking here of a useful example, but here's a not-useful example:

cp file1 >(grep xyz)

I say this isn't useful because why use the "cp" command? Why not:

cat file1 | grep xyz

Or better yet:

grep xyz file1

Most shell commands write their primary output to STDOUT. I can think of some examples that don't, like giving an output file to tcpdump, or the object code out of gcc, but I can't imagine wanting to pipe that into another command.

If you can think of a good use case, let me know.


VARIATION 2 - REDIRECTING STANDARD I/O

Here's something that I have occasionally wanted to do. Pipe a command's STDOUT to one command, and STDERR to a different command. Here's a contrived non-pipe example:

process_foo 2>err.tmp | format_foo >foo.txt
alert_operator <err.tmp
rm err.tmp

You could re-write this as:

process_foo > >(format_foo >foo.txt) 2> >(alert_operator)

Note the space between the two ">" characters - this is needed. Without the space, ">>" is treated as the append redirection.

Sorry for the contrived example. I know I've wanted this a few times in the past, but I can't remember why.


And for completeness, you can also redirect STDIN:

cat < <(echo hi)

But this is the same as:

echo hi | cat

I can't think of a good use for the "< <(cmd)" construct. Let me know if you can.


EDIT:

I'm always amused when I learn something new and pretty quickly come up with a good use for it. I had some files containing a mix of latency values and some log messages. I wanted to "paste" the different files into a single file with multiple columns to produce a .CSV. But the log messages were getting in the way.

paste -d "," <(grep "^[0-9]" file1) <(grep "^[0-9]" file2) ... >file.csv

Done! :-)

Tuesday, November 9, 2021

Keychron K2 Keyboard

 I mentioned buying a Keychron K2 keyboard almost two years ago, but that post was primarily about a different vendor's keyboard which was a fail.

I just bought a second Keychron K2 keyboard ("blue" switches), but not because of a problem. It's because the keyboard is wonderful, and I want a second one to keep at an alternate worksite.

The laptop keyboard on the 2017-vintage Macbook Pro is almost unusable. Really, even the 2015-vintage Air's laptop keyboard is not that great. I prefer a full-stroke "clicky" keyboard with good tactile feedback.

Enter the Keychron K2. Lots of nice features that I won't bother listing since I don't use most of them and the site explains them fine. I like the noisy "blue" style switches, but you can get quieter ones.

Also, it has all the Mac-specific special keys, right there (I don't like the touch-bar at the top of the Macbooks.) And I also like the compact size.

My only complaint is that the key caps are not dual-injected, which means that the paint can wear off the tops of the frequently-used keys (E and A). But this is a problem for most keyboards I use; I apparently have a heavy typing hand.

Count me as a satisfied customer.

Thursday, August 5, 2021

Timing Short Durations

 I don't have time for a long post (HA!), but I wanted to add a pointer to https://github.com/fordsfords/nstm ("nstm" = "Nano Second Timer"). It's a small repo that provides a nanosecond-precision time stamp portably between MacOS, Linux, and Windows.

Note that I said precision, not resolution. I don't know of an API on Windows that gives nanosecond resolution. The one Microsoft says you should use (QueryPerformanceCounter()) always returns "00" as the last two decimal digits. I.e. it is 100 nanosecond resolution. They warn against using "rdtsc" directly, although I wonder if most of their arguments are mostly no longer applicable. I would love to hear if anybody knows of a Windows method of getting nanosecond resolution timestamps that is reliable and efficient.

One way to measure a short duration "thing" is to time doing the "thing" a million times (or whatever) and take an average. One advantage of this approach is that taking a timestamp itself takes time; i.e. making the measurement changes the thing you are measuring. So amortizing that cost over many iterations minimizes its influence.

But sometimes, you just need to directly measure short things. Like if you are histogramming them to get the distribution of variations (jitter).

I put some results here: https://github.com/fordsfords/fordsfords.github.io/wiki/Timing-software


Friday, July 9, 2021

More Perl "grep" performance

In an earlier post, I discovered that a simple Perl program can outperform grep by about double. Today I discovered that some patterns can cause the execution time to balloon tremendously.

I have a new big log file, this time with about 70 million lines. I'm running it on my newly-updated Mac, whose "time" command has slightly different output.

Let's start with this:

time grep 'asdf' cetasfit05.txt
... 39.388 total

time grep.pl 'asdf' cetasfit05.txt
... 21.388 total

About twice as fast.


Now let's change the pattern:

time grep 'XBT|XBM' cetasfit05.txt
... 24.787 total

time grep.pl 'XBT|XBM' cetasfit05.txt
... 18.940 total

Still faster, but nowhere near twice as fast. I don't know why 

Now let's add an anchor:

time grep '^XBT|^XBM' cetasfit05.txt
... 25.580 total

time grep.pl '^XBT|^XBM' cetasfit05.txt
... 3:08.25 total

WHOA! Perl, what happened????? 3 MINUTES???

My only explanation is that Perl tries to implement  a very general regular expression algorithm, and grep implements a subset, and that might cause Perl to be slow in some circumstances. For example, maybe the use of alternation with anchors introduces the need for "backtracking" under some circumstances, and maybe grep doesn't support backtracking. In this simple example, backtracking is probably not necessary, but to be general, Perl might do it "just in case". (Note: I'm not a regular expression expert, and don't really know when "backtracking" is needed; I'm speculating without bothering to learn about it.)

Anyway, let's make a small adjustment:

time grep.pl '^(XBT|XBM)' cetasfit05.txt
... 17.910 total

There, that got back to "normal".

I guess multiple anchors in a pattern is a bad idea.


P.S. - even though this post is about Perl, I tried one more test with grep:

time grep 'ASDF' cetasfit05.txt
... 26.132 total

Whaaa...? I tried multiple times, and lower-case 'asdf' always takes about 40 seconds, and upper-case 'ASDF' always takes about 27 seconds. I DON'T UNDERSTAND COMPUTERS!!! (sob)

Wednesday, March 17, 2021

Investment Advice from an Engineer

 I have some financial advice regarding investing in stocks. But be aware that, while I am pretty wealthy, the vast majority of my wealth came from salary from a good-paying career. You will *NOT* get rich off the stock market by following my advice.


THE ADVICE

Put money every month into an U.S. exchange-traded fund that is very broad market. Like SPDR. (I prefer VTI because it is even broader and has lower fees, but the differences aren't really that big). The goal is to keep buying and never selling, every working month of your life until you retire. (I don't have retirement advice yet.)

If the market starts going down, do *NOT* stop buying. In fact, if you can afford it, put more in. Every time the market goes down, put more in. The market will go back up, don't worry. 

The same cannot be said for an individual stock -- sometimes a company's stock will dive down and then stay down, basically forever. But the market as a whole won't do that. A dive might take a few days to recover, or might take a few years to recover. But it will recover. DON'T sell a broad fund if the market is going down. BUY it.


AND THIS WILL GET ME RICH?

No. It will give you the highest probability of a good return. Back when I was a kid, I was told to put money into a bank savings account. That was poor advice then, and is terrible advice now with interest rates close to zero. Putting money into a guaranteed bank account is guaranteed to underperform inflation. I.e. it will slowly but surely lose value.

Instead, tie your money to the overall market. The broad market has its ups and downs, but if you stick with it for a while, the overall trend is higher than inflation. 


WHAT IF I WANT TO GET RICH QUICK?

Well, you could buy a lottery ticket. That will get you rich the quickest. Assuming you win. Which you won't. Or you could go to Vegas and put a quarter into a slot machine.

But you're smarter than that. You know the chances of getting rich off of lotteries or gambling are too low. You want something that has some risk, but which will probably make you rich. And you're thinking the stock market.

Your best bet? Find a company currently trading for a few dollars a share, but is definitely for sure going to be the next Apple or Microsoft. One tiny problem: if it is definitely for sure going to be the next Apple or Microsoft, the stock price won't be a few dollars a share. It will be priced as if it already IS the next Apple or Microsoft. This is because there are tens of thousands of smart traders out there who are spending a HELL of a lot more time than you are trying to find the next big company. For a "sure thing" company that is already publicly traded, those tens of thousands have already bid up the price.

The only real chance for you to get in on the ground floor is to find a garage shop start-up, and invest in them. I have a rich friend who has made a lot of money doing exactly that. For every ten companies he invests in, nine go bankrupt within 5 years. And one goes off like a rocket.

That's how you do it. And unfortunately, you have to start out pretty rich to make this work. And you need to research the hell out of startups, and have a good crystal ball.

The only other way to do it is to find a company that the tens of thousands of smart traders thinks will NOT be a big deal, but you believe something they don't. Microsoft was publically traded at a low price for many years. The tens of thousands of smart traders in the 70s didn't think home computers would become a thing. And the few people who believed otherwise became rich.

The problem is that belief usually doesn't work very well at predicting success.

Look at BitCoin. I know several people who have made huge amounts of money on BitCoin. They did their initial investments based on a belief. A belief that BitCoin would become a real currency, just like dollars and euros; that people would be use BitCoin every day to buy and sell everything from gasoline to chewing gum. They looked at the theories of money and the principles of distributed control, and thought it would definitely for sure replace national currencies.

Those friends of mine were wrong. They made money for a completely different reason: speculators. Speculators buy things that are cheap and they think will go up in price. If enough speculators find the same thing to buy, the prices *does* go up. And more speculators jump in. BitCoin is a big speculative bubble, with almost no intrinsic value. (And yes, I know BitCoin is more complicated than that. But I stand by my 10,000-foot summary.)

Now don't get me wrong. Successful speculators DO become rich. Who am I to argue with success? But getting rich off of speculation is all about timing. You have to find the next big thing before most of the other speculators do, and then jump back out *before* it has run its course. Will BitCoin come crashing back down? Not necessarily. If enough people simply *believe* in it, it will retain its value. My own suspicion is that it will eventually crash but what do I know? I thought it would have crashed by now.

That's also what happened with GameStop. A group of Reddit-based speculators decided to pump up the price of a company. If you were in on it from the start, you probably made a ton of money. But once it hit the news, it was too late for you to get rich off of it. The best you could hope for was to make a little money and then get out FAST. But most people who jumped into GameStop after it had already made the news ended up losing money.

(BTW, "pump-and-dump" is against the law. I will be interested to find out if any of the Reddit-based traders get in trouble.)

Anyway, I know of many people who have taken a chance on a stock, and made some money. But they didn't get rich. And if they keep trying to replicate their early success, they'll end up winning some and losing some. And if they're smart, and work hard at it, they may out-perform the overall market in the long run. But remember - those tens of thousands of smart traders are also trying to out-perform the overall market. For you to do it repeatedly for many years probably requires expertise that those smart traders don't have. And you don't get rich quick this way, you just make some good money.


WHAT IF I JUST WANT TO PLAY THE MARKET

(shrugs) Everybody needs a hobby. I have a friend who goes to Vegas once a year. Sometimes he comes back negative, sometimes positive. He has absolutely no illusion that he will get rich in Vegas. He assumes he will either make a little or lose a little. And he has fun doing it. There's nothing wrong with spending money to have fun.

If you play the stock market as a game, where you aren't risking your financial future, then more power to you. But I knew one person who had to stop for his own emotional well-being. He started feeling bad every time he lost some money because he should have invested less, but also felt bad when he made money because he should have invested more. Overall he made money, but he had so much anxiety doing it that he decided it wasn't worth it.

Sunday, March 14, 2021

Circuit simulation

 I've been playing with designing simple digital circuits this weekend. Since my breadboards are not with me at the moment, I decided to look for circuit simulators.

Here's a nice comparison of several: https://www.electronics-lab.com/top-ten-online-circuit-simulators/

Before I found that comparison site, I tried out https://www.circuitlab.com/ and even threw them money for a month's worth. And I can say that I've gotten that much worth of enjoyment out of my tinkering this weekend, so money well-spent. But I knew that I didn't want to keep shelling out every month (I don't do digital design that much), and there was no way to export the circuits in a way that I could save them. So I kept looking.

Here's my CircuitLab home: https://www.circuitlab.com/user/fordsfords/

I haven't tried all the choices in the "top ten" list, but I did try the "CircuitJS1" simulator maintained by Paul Falstad and Iain Sharp. See https://github.com/sharpie7/circuitjs1 It isn't quite as nice as CircuitLab, but it's hard to argue with free, especially given my infrequency of use.

CircuitJS1 doesn't host users' designs. In fact, they don't integrate well with any form of storage. You can save your design to a local file, but the simulator doesn't do a good job of remembering file names. It presents you with a link containing a file name of the form "circuit-YYYYMMDD-HHMM.circuitjs.txt". You can save the linked contents with your own file name, but the next time you go to save, it obviously won't remember that name since it was a browser operation. All of this will make it a little inconvenient and perhaps error-prone to manage different projects. If I were doing a lot of hardware work, I would probably choose something else. But for occasional fiddling, this is fine.

Here's a simple state machine that checks even/odd parity of an input bit stream: http://www.falstad.com/circuit/circuitjs.html?startCircuitLink=https://www.geeky-boy.com/test.circuitjs.txt

If I want to make anything public, I'll make them as github projects.

Friday, January 8, 2021

Racism in America

 As my readers have no doubt noticed (all 2 of you!), I keep this blog pretty technical, without a lot of politics. And I intend to keep it that way ... for the most part. But occasionally I will let my politics peek out.

Yeah, you're expecting me to talk about the events in Washington DC in January, 2021. I might post about that some day, but I'm nowhere near ready yet.

No, I'm going to talk about a class I took last fall. See https://www.rootstorevolution.org/courses

These are left-leaning classes that not only teach history, they also encourage and facilitate activism. Their focus is on racism, but touch on other "isms" as well. I learned a heck of a lot of history that wasn't covered very well back when I went to high school. The material is well-researched and well-sourced. I consider myself a better person for having participated.

The bottom line is that it isn't enough to be "not racist". We have to be "anti-racist".

The classes are not cheap. As of this writing, they are $200 a pop. (And worth it, in my humble opinion.) That said, the class organizers don't want cost to be a barrier to participation, and are willing to make adjustments. Plus, I am willing to kick in $100 for anybody who comes to them from my recommendation. Tell 'em fordsfords sent ya. (-:

Anybody who wants more "informal" information on the classes, send me an email.

Steve

Sunday, November 29, 2020

Using sed "in place" (gnu vs bsd)

 I'm not crazy after all!

Well, ok, I guess figuring out a difference between gnu sed and bsd sed is not a sign of sanity.

I use sed a fair amount in my shell scripts. Recently, I've been using "-i" a lot to edit files "in-place". The "-i" option takes a value which is interpreted as a file name suffix to save the pre-edited form of the file. You know, in case you mess up your sed commands, you can get back your original file.

But for a lot of applications, the file being edited is itself generated, so there is no need to save a backup. So just pass a null string in as the suffix. No problem, right?


[ update: useful page: https://riptutorial.com/sed/topic/9436/bsd-macos-sed-vs--gnu-sed-vs--the-posix-sed-specification ]

 

GNU SED (Linux and Cygwin)

echo "x" >x
sed -i '' -e "s/x/y/" x
sed: can't read : No such file or directory

Hmm ... that's odd. It's trying to interpret that null string as a file name, not the value for the "-i" option. Maybe it doesn't like that space between the option and the value.

echo "x" >x
sed -i'' -e "s/x/y/" x

There. It worked. I'm generally in the habit of using a space between the option and the value, but oh well. Learn something new every day...


BSD SED (FreeBSD and Mac)

echo "x" >x
sed -i'' -e "s/x/y/" x
ls x*
x    x-e

Hey, what's that "x-e" file? Oh, it IGNORED the empty string and interpreted "-e" as the suffix! Put the space back in:

echo "x" >x
sed -i '' -e "s/x/y/" x

Works. No "x-e" file.


ARGH!

I use both Mac and Linux, and want scripts that work on both!

 

THE SOLUTION

Go ahead and always generate a backup file. And don't use a space between the option and the value. This works on both:

echo "x" >x
sed -i.bak -e "s/x/y/" x
rm x.bak

Works on Mac and Linux.

IT TOOK ME A LONG TIME TO FIGURE ALL THIS OUT!!! Part of the reason it took so long is that for the cases that don't work as intended, they tend to basically work. For example, the first Linux case where it tried to interpret '' as a file. It printed an error. But then it went to the actual file and processed it correctly. The command did what it was suppose to do, but it printed an error. For the BSD case, it created a backup file using "-e" as the suffix, but it went ahead and interpreted the sed command string as a command string, and properly processed the file. In both cases, the end goal was accomplished, but with unintended side effects.

Corner cases: the bane of programmers everywhere.

Friday, November 27, 2020

Sometimes you need eval

 The Unix shell usually does a good job of doing what you expect it to do. Writing shell scripts is usually pretty straight-forward. Yes, sometimes you can go crazy quoting special characters, but for most simple file maintenance, it's not too bad.

I *think* I've used the "eval" function before today, but I can't remember why. I am confident that I haven't used it more than twice, if that many. But today I was doing something that seemed like it shouldn't be too hard, but I don't think you can do it without "eval".

RSYNC

I want to use "rsync" to synchronize some source files between hosts. But I don't want to transfer object files. So my rsync command looks somewhat like this:

rsync -a --exclude "*.o" my_src_dir/ orion:my_src_dir

The double quotes around "*.o" are necessary because you don't want the shell to expand it, you want the actual string *.o to be passed to rsync, and rsync will do the file globbing. The double quotes prevents file glob expansion. And the shell strips the double quotes from the parameter. So what rsync sees is:

rsync -a --exclude *.o my_src_dir/ orion:my_src_dir

This is what rsync expects, so all is good.

PUT EXCLUDE OPTIONS IN A SYMBOL: FAIL

For various reasons, I wanted to be able to override that exclusion option. So I tried this:

EXCL='--exclude *.o'  # default
... # code that might change EXCL
rsync -a $EXCL my_src_dir/ orion:my_src_dir

But this doesn't work right. The symbol "EXCL" will contain the string "--exclude *.o", but when the shell substitutes it into the rsync line, it then performs file globbing, and the "*.o" gets expanded to a list of files. For example, rsync might see:

rsync -a --exclude a.o b.o c.o my_src_dir/ orion:my_src_dir

The "--exclude" option only expects a single file specification.

SECOND TRY: FAIL

So maybe I can enclose $EXCL in double quotes:

rsync -a "$EXCL" my_src_dir/ orion:my_src_dir

This passes "--exclude *.o" as a *single* parameter. But rsync expects "--exclude" and the file spec to be two parameters, so it doesn't work either.

THIRD TRY: FAIL

Finally, maybe I can force quotes inside the EXCL symbol:

EXCL='--exclude "*.o"'  # default
... # code that might change EXCL
rsync -a $EXCL my_src_dir/ orion:my_src_dir

This almost works, but what rsync sees is:

rsync -a --exclude "*.o" my_src_dir/ orion:my_src_dir

It thinks the double quotes are part of the file name, so it won't exclude the intended files.

EVAL TO THE RESCUE

The solution is to use eval:

EXCL='--exclude "*.o"'  # default
... # code that might change EXCL
eval "rsync -a $EXCL my_src_dir/ orion:my_src_dir"

The shell does symbol substitution, so this is what eval sees:

rsync -a --exclude "*.o" my_src_dir/ orion:my_src_dir

And eval will re-process that string, including stripping the double quotes, so this is what rsync sees:

rsync -a --exclude *.o my_src_dir/ orion:my_src_dir

which is exactly correct.

P.S. - if anybody knows of a better way to do this, let me know!

EDIT: The great Sahir (one of my favorite engineers) pointed out a shell feature that I didn't know about:;

Did you consider setting noglob? It will prevent the shell from expanding '*'. Something like:

    EXCL='--exclude *.o' # default
    set -o noglob
    rsync -a $EXCL my_src_dir/ orion:my_src_dir
    set +o noglob

I absolutely did not know about noglob! In some ways, I like it better. The goal is to pass the actual star character as a parameter, and symbol substitution is getting in the way. Explicitly setting noglob says, "hey shell, I want to pass a string without you globbing it up." I like code that says exactly what you mean.

In contrast, my "eval" solution works fine, but the code does not make plain what my purpose was. I would need a comment that says, "using eval to prevent  the shell from doing file substitution in the parameter string." And while that's fine, I much prefer code that better documents itself.

One limitation of using noglob is that you might have a command line where you want parts of it not globbed, but other parts globbed. The noglob basically operates on a full line. So you would need to do some additional string building magic to get the right things to be done at the right time. But the same thing would be true if you were using eval. Bottom line: the shell was made powerful and flexible, but powerful flexible things tend to have subtle corner cases that must be handled in non-obvious ways. No matter what, a comment might be nice.

Tuesday, November 17, 2020

Ok, I guess I like Grammarly (grumble, grumble)

Ok, I grudgingly admit that I like Grammarly.


My complaints still hold: [UPDATE: these are all fixed now]

  1. Mac users are second-class citizens. Mac Word integration has the file size limit, and there is no Mac outlook integration. [UPDATE: Mac integration is now good]
  2. Their desktop tool won't edit a locally-stored text file. You have to do cutting and pasting. [UPDATE: it integrates well with TextEdit. But not vim.]
  3. The file size limit is too small for serious work. Yes, you can do cutting and pasting again, but really? In 2020? [UPDATE: it now operates on large files]


The grumpy old man in me really wants to mumble something about snot-nosed little kids and go back to a typewriter and liquid paper.


But ... well ... I do have some bad writing habits.


Mostly I sometimes write unnecessarily complicated sentences, including useless phrases that I must have learned sound intellectual. It's a little humbling to have it pointed out over and over, but the result of more concise writing is worth it.


Mind you, there are many MANY times that I click the trash can because I don't like Grammarly's suggestions. In much of my technical writing, I use passive voice because active is too awkward. I also deviate from the standard practice of including punctuation inside quotes, especially when the quotes are not enclosing an actual quotation, but instead are calling out or highlighting a technical term, like a variable name. If I tell you to enter "ls xyz," and you type the comma, it won't work. You have to enter "ls xyz". I also sometimes include a comma that Grammarly thinks is not needed, but I think it helps separate two ideas.


Also, Grammarly isn't good at large-scale organization of content, which can have a MUCH greater effect on clarity than a few superfluous words.


In other words, *real* editors don't have to worry about being replaced by AIs for quite a while.


And yet ... and yet ... even with its limited ability to understand what I'm trying to say, it is still improving my writing. In small ways, perhaps. But improvement is improvement.


So yeah, I'll keep paying them money (grumble, grumble).

Friday, October 30, 2020

Software Sucks

 Sorry, I had to say it. Software really does suck.

We just installed a new CentOS, and I wanted to do some apache work. I don't do that kind of thing very often, so I don't just remember how to do it. Thank goodness for search engines!

Do a quick google for "apache shutdown" which led me to https://httpd.apache.org/docs/2.4/stopping.html which tells me to do a "apachectl -k graceful-stop". Cool. Enter that command.

Passing arguments to httpd using apachectl is no longer supported.
You can only start/stop/restart httpd using this script.
If you want to pass extra arguments to httpd, edit the
/etc/sysconfig/httpd config file.

Um ... stopping httpd is exactly what I was trying to do. So I guessed that 2.4 must be old doc. Rather than trying to find new doc, I just entered

apachectl -h

It responded with:

Usage: /usr/sbin/httpd [-D name] [-d directory] [-f file]
                       [-C "directive"] [-c "directive"]
                       [-k start|restart|graceful|graceful-stop|stop]
                       [-v] [-V] [-h] [-l] [-L] [-t] [-T] [-S] [-X]
Options:
...

There's the "-k graceful-stop" all right. What's the problem? Well, except of course, for the stupid fact that the Usage line claims the command is "httpd", not "apachectl". Some newbie must have written the help screen for apachectl.

Another search for "Passing arguments to httpd using apachectl is no longer supported" wasn't very helpful either, but did suggest "man apachectl". Which says:

When  acting in pass-through mode, apachectl can take all the arguments available for the httpd binary.
...
When acting in SysV init mode, apachectl takes simple, one-word commands, defined below.
...

How might I know which mode it's working in? Dunno. But a RedHat site gave an example of:

apachectl graceful

which matches the SysV mode. So apparently the right command is "apachectl graceful-stop" without the "-k". Which worked.

So why did "apachectl -h" give bad help? I think it just passed the "-h" to httpd (passthrough), so the help screen was printed by httpd. But shouldn't apachectl have complained about "-h"? GAH!

Software sucks.

Wednesday, October 14, 2020

Strace Buffer Display

 The "strace" tool is powerful and very useful. Recently a user of our software sent us an strace output that included a packet send. Here's an excerpt:

sendmsg(88, {msg_name(16)={sa_family=AF_INET, sin_port=htons(14400), sin_addr=inet_addr("239.84.0.100")}, msg_iov(1)=[{"\2\0a\251C\27c;\0\0\2\322\0\0/\263\0\0\0\0\200\3\0\0", 24}], msg_controllen=0, msg_flags=0}, 0) = 24 <0.000076>

Obviously there's some binary bytes being displayed. I see a "\0a", so it's probably hex. But wait, there's also a \251. Does that mean 0x25 followed by ascii '1'? I decoded it assuming hex, and the packet wasn't valid.

So I did a bit of Googling. Unfortunately, I didn't note where I saw it, but somebody somewhere said that it follows the C string conventions. And C strings come from long ago, when phones had wires connecting them to wall jacks, stack overflow was a bug in a recursive program, and octal ruled the waves when it came to specifying binary data.

So \0a is 0x00 followed by ascii 'a' and \251 is 0xa9. Now the packet parses out correctly. (It's a "Session Message" if you're curious.)

So, I guess I'm a little annoyed by that choice as I would prefer hex, but I guess there's nothing all that wrong with it. Hex or octal: either way I need a calculator to convert to decimal. (And yes, I'm sure some Real Programmers can convert in their heads.)