Hacking ls -l

http://www.lemis.com/grog/diary-oct2012.php?topics=c#D-20121012-233520

by drp4929 • 14 years ago

199 88 14 years ago

cheald3• 14 years ago

While I appreciate the story, what's wrong with `ls -lh`?

ghostfish• 14 years ago

My thoughts exactly. This is just complexity for complexity's sake. Useful as an exercise, but the -h flag already does this is an even more readable manner.

bajsejohannes• 14 years ago

This works with sorting, and it's easier to pick big files out at a glance. I would use this as often as -h

pepve• 14 years ago

I guess people can be very different in this respect. I really need the full number (or at least all of the numbers in the same unit) to be displayed. I don't find the 'human' format helpful at all when looking at ls output.

sliverstorm3• 14 years ago

It just depends what info you desire. I typically use "ls -lh" to quickly find large files to clean up to recover disk space.

paddyoloughlin• 14 years ago

For me, -h makes it more difficult to quickly compare the sizes of files in one list by glance. This is something that I have to do often enough that it has prevented me from adding -h to my ls alias. I'd have to use it for a bit to be sure, but the post's suggestion seems a pretty good 'best of both worlds' solution to me.

dredmorbius2• 14 years ago

This.

I run into the situation more often with 'du' (when trying to find which subdirectory tree has excess junk in it), to the point that, while 'du -h' is human readable, it's not particularly sortable so:

    du -hs $( du -s * | sort -k1nr,1 -k2 | head )

.... which will return the human-readable output, based on numerically sorting the full numeric output. Eyeball comparisons are easier as you're aware that results are already sorted by size.

zapman449• 14 years ago

Or, you could use 'ls -h'...

(that said, I do see the utility, since it gives a more obvious visual queue as to the order of size differences... but if you're doing anything with the sizes programatically, you have to remove the commas afterwards... Short version: if you're going to do this, make it a unique flag, or a new flag modifier to the -l flag... don't overload the -l flag without recourse...)

Evbn3• 14 years ago

Ideally a parser should respect locale, and use a sane format (not commas) for multiple numbers in a list.

Even better if the _ separator used by programming languages were a supported locale LC=C_FOR_HUMANS :-)

guylhem6• 14 years ago

Is this front page worth materiel? I mean, it's good you took the time to add a ', but doing the same with sed would have been faster.

Alternatively, do you know about ls -lhrS? It will print size in human formats and reverse sort the files by size - ie the bigger will be at the end of the list

drp4929• 14 years ago

Last sentence in the post says it all. Hacking is more than just coding and the steps he followed are illustrative in general.

memset3• 14 years ago

Yes, it is front-page worthy, because the details give us insight into how one might make any sort of change to a codebase like this. "If you want to be a hacker, these are specific steps I took to hack something up." In a domain that most of us are not very familiar with!

guylhem6• 14 years ago

Editing ls/print.c sourcecode and recompiling is not hacking in my definition.

I usually consider the portability of the solution. I have linux i386 and x64 machines, my arm n900, an osx latop, etc.

Recompiling ls (or, heavens forbid, cross compiling!) for each machine may be a bright idea.

Adding a line to your profile that will take advantage of the existing tools like sed is closer to hacking in my definition, because it tries to think about the bigger problem - but still I wouldn't dare calling the following "hacking":

echo "alias lll=\"ls -l | sed -e :a -e 's/\(.*[0-9]\)\([0-9]\{3\}\)/\1,\2/;ta'\"">> ~/.bashrc

halostatue• 14 years ago

More to the point, it also shows that an "easy" change isn't so easy. In the course of solving this "easy" change, the author added six new items to his personal to-do list.

As edw519 has said, a one line code change takes six days to implement.

FuzzyDunlop• 14 years ago

Yes, because it's interesting, and because for the OP in particular they've spent a little bit of effort up front to save themselves time in the long run, and learn something too.

salgernon• 14 years ago

Anyone who has ever had to work on a large system will instantly recognize what he's done here, and admire his approach, and light a candle in support of ever getting this patched all the way through the various broken projects. Remember, he's got to get a patch approved for gcc to get this to work, and only once that is done, in production, and generally available will he be able to submit a patch for ls. This is the reality of disparate projects with many maintainers and schedules. This may seem to be a trivial example, but it is entirely indicative of the process.

thaumasiotes• 14 years ago

Surely the appropriate option character for this new, human-readable output is "-h".

Makes you wonder whether anyone ever considered the problem before...

chris_wot3• 14 years ago

Human readable form in bytes? I thought it you had a file greater than a megabyte hen it shows in MB? What if you want to read it in bytes with the thousands separator?

memset3• 14 years ago

Guys! The point of this article is not to prescribe the only method of displaying human-readable file sizes. Obviously one could use `ls -lh`; the author clearly demonstrates that he is willing and able to read man pages to find answers.

Rather, this is a pretty interesting look into what it actually entails to make what ought to be a very simple and straightforward change.

It turns out that these simple changes are hard! Not just in identifying the piece of code to modify, but that man pages are often incomplete or unclear. It also illustrates the complexities behind making software portable - in this case, using the nation-neutral place separator. It also reminds us that solving what is on the surface a simple problem lets one uncover all sorts of interesting and messy details underneath - including more problems to solve!

These are steps that he'd have to take no matter what the code or feature. This article is not "complexity for complexity's sake", it's illustrating the complexity of making changes to any piece of code - and that it is surprisingly difficult for something that one would think is very easy!

guylhem6• 14 years ago

It is not very easy because it is an unusual request.

But I still wonder if this is easier than ls -l | sed -e :a -e 's/\(.*[0-9]\)\([0-9]\{3\}\)/\1,\2/;ta' ??

The investigations would be interesting it they were more complete, i.e. if the actual result was a change in the locale which could be appliable to other tools printing numbers besides ls (in the author TODO).

I mean, will it work with bc?

At the moment it's not better than an shell script alias giving the output to sed, but it is more complex - you have to recompile a binary for every OS you use.

dalke5• 14 years ago

When I use your sed transformation on one of my directories, I see entries like:

    drwxr-xr-x  1,653 dalke  admin       56,202 Mar  5  2,012 pubchem
    -rw-r--r--     1 dalke  staff       59,252 Nov 16  2,011 pubchem_10,000.fps.0.9.cluster

I don't want to see the year written "2,012", and the file name is 'pubchem_10000" not "pubchem_10,000".

pilgrim689• 14 years ago

Your solution is the better one, but that does not take anything away from memset's argument, though... This is not about the solution. This is about the problem of having all these yaks to shave just to add a comma to some program's output.

cheald3• 14 years ago

On the other hand, you could consider it a cautionary tale about not reinventing wheels, because a problem that may seem trivial at first often turns out to be far more complex than expected.

This is why you try to re-use work when possible, rather than endlessly reinventing things, because while sure, adding a comma to the printf string is easy enough, your assumptions (English locale, compiler not trying to be clever) are going to quickly become visible as things fall apart because your assumptions aren't in line with the system's assumptions.

What this story really demonstrates is that without a clear understanding of how a system is designed and the basic assumptions it makes, just "hacking on the code" is just as likely to break things as it is to fix them.

StavrosK• 14 years ago

If your definition of "breaking" things is "they don't work on the first try", everything I've ever tried to do was broken.

geofft• 14 years ago

You assume that systems tend to be well-designed and the basic assumptions it makes are justifiable, and that the systems faithfully implement that design and those assumptions.

It sounds like the author found a bunch of bugs in the process of making a simple code change. That happens pretty frequently, and doesn't mean that the author should let the priests of the cathedral deal with this UNIX thing that is too complicated for the laity to hack on. It just means there is no priesthood.

DanBC2• 14 years ago

> It turns out that these simple changes are hard! Not just in identifying the piece of code to modify, but that man pages are often incomplete or unclear.

This is a great shame. I like OpenBSD's approach to man pages - incorrect documentation is a bug and can be as severe as a bug in code; correct documentation is important.

Fixing up man pages is something that non-technical volunteers could help with, except when it's hard to grok what the code actually does vs what it should do.

emillon• 14 years ago

> Fixing up man pages is something that non-technical volunteers could help with

Another problem with that is that most tools used in this process are made with technical users in mind. A lot of people can expand documentation, but sending manpages patches in a bug tracker is a technical step.

3amOpsGuy• 14 years ago

Mountain, meet molehill.

secure• 14 years ago

In case anyone wonders, I recently looked into how locales work with respect to LANG, LC_ALL and LC_*: http://c.i3wm.org/6799926

By the way, by looking at http://www.lemis.com/grog/index.php you can see that the author uses FreeBSD, just in case you were wondering about /usr/src

pixelbeat• 14 years ago

I enable this for GNU ls like:

    alias ls="BLOCK_SIZE=\'1 ls --color=auto"

The above is a bit hacky and not very UNIXy as it's lumping more logic into ls, rather than splitting out into functional units.

Number formatting being a very common requirement, I've proposed a design for a new numfmt GNU coreutil

http://lists.gnu.org/archive/html/coreutils/2012-02/msg00085...

which would be used like:

    ls -l | numfmt --field=5 --format=%'d

Aardwolf3• 14 years ago

I really don't understand why block size is 512 by default. It should really be 1 by default.

Except for someone with an ancient hard disk who thinks in blocks instead of (mega, giga, etc...)bytes, who ever needs or wants that?

alayne• 14 years ago

512 byte blocks for ls is specified by POSIX. That would probably be a painful change now.

fafner• 14 years ago

Why not

    alias ls="ls --block-size=\'1 --color=auto"

osteele• 14 years ago

Mr. Lehey managed to improve the system in such a way that it will subsequent changes for him and others easier, independently of whether the specific change to `ls` is never adopted. It's “five whys” applied to “why is this hard” and “how can I make it easier”. It's more effort, with a greater chance that much of it will survive the current context and requirements.

Some people improve the area they travel through, others leave debris, and many are noops who make no difference to those who come after. If there's not enough entropy fighters like Mr. Lehey working a system, it turns to kipple.

jrockway4• 14 years ago

Most annoying is that gcc warns about perfectly valid and logical code. That causes people to ignore warnings, and before you know it, you have a piece of software that has more warnings than lines of code.

Alternatively, when you cleverly figure out how to work around the warning, like the author does, you now prevent that rule from triggering even when it's right. Clearly a better unit test is needed.

Evbn3• 14 years ago

That warning seems like a nasty hack anyway, if the compiler can't inline a local when running safety checks.

It is super scary that the compiler appears to be using a different constant from printf for its format checker, that shows it probably isn't using a pattern supplied by printf.

jrockway4• 14 years ago

Yes to both points. I haven't read the source code, but this feels like a case of code-oriented-programming instead of data-oriented-programming. In other words, they write printf twice: once in the C library, and once in the warning system. A more careful programmer might write both in terms of a ruleset that's declared a single time.

(Or they did that and it's just a bug somewhere.)

TwoBit• 14 years ago

The printf ' format specifier is not Standard C. It's in neither the C99 Standard nor the new C11 Standard. So it's not actually valid, and it's a coincidence if it happens to work with your Standard Library.

Consider that the compiler generating that warning knows only Standard C, and in fact you could be pairing it with any C library, including those that are strictly conforming and don't support the ' extension.

jrockway4• 14 years ago

You're arguing that the GNU C Library is incompatible with the GNU Compiler Collection?

(In the example, he's compiling ls with the -std=gnu99 flag, which means he's targeting GNU, not C99 or C90 or C11 or POSIX or any other standard.)

lelf• 14 years ago

> Alternatively, when you cleverly figure out how to work around the warning,

Or just read the docs (it should be "%'*jd "). Then no warnings. (IIRC ' is in C99 and -std=gnu99 targets c99 + gnu extensions.)

The same story with the rest. Two ways of doing things — learn & think and just do it right or twiddle until it seems to likely maybe work (possibly). The article is about the latter. Plus "blame the compiler".

dsr_• 14 years ago

Now let's consider software lifecycle in a large context: longevity of forks.

If he doesn't send the changes off to upstream, and make a case good enough for them to be approved, then all this dooms him to maintaining his fork on all the platforms where he wants it until he gets sick of it or convinces someone else to do it for him.

cjg_• 14 years ago

FYI, Greg Lehey is a longtime FreeBSD committer.

Aardwolf3• 14 years ago

Man, such fragile stuff. Why not code a function yourself that turns a number into a string representing it decimally with the commas every three digits. I normally like and use good library functions and standards, but if they're that fragile and depend on your environment then no thanks.

michael_h• 14 years ago

not everyone uses commas to separate their number groupings. his solution will work for any locale.

Aardwolf3• 14 years ago

Yes, in my country we use spaces to separate thousands and "," is used for what the decimal point does in the US. In my handwriting I use that notation.

However, from a computer, I (and I'm certain I'm not the only one) actually expect it to output the US notation.

I'd much rather have a computer always output the same format (and that happens to be the US format), than try to be smart with locales, when the end result is that some things will do this, others that. Makes stuff harder to use, and when programming, harder to parse.

I've once had to touch Excel on a Windows machine configured for a non-US language, and it refused to import a CSV file that had commas, even though CSV means comma separated values. It required semicolons due to the locale settings of Windows. This stuff should not happen. A CSV is meant for computers, and to be interchangeable, not to use different types of commas and refuse to work with other types depending on user locale settings...

Of course, when publishing or printing, that's a whole different matter, and there it better get the locale of your country perfect. But this here was about output in the console, which is often meant as input of other scripts etc...

barrkel• 14 years ago

Because that would not be correct in Germany or other locales which use . for digit group separation and , for the decimal separator.

codegeek• 14 years ago

i always use one hack for ls. alias lsd="ls -ltrF | grep ^d"

This way, I quickly run lsd to only look for directories.

Evbn3• 14 years ago

But lsd makes you see things that aren't even there.

andreasvc• 14 years ago

That's funny, I also have an alias for lsd which does this. But you can do it without grep: lsd='ls -d */'

bgaluszka• 14 years ago

Yours doesn't show . directories and parents does.

lucian303• 14 years ago

-h

chris_wot3• 14 years ago

Not for files greater than a MB.

joeyh• 14 years ago

Incidentially, I completed ls's set of -a-z options recently.

http://joeyh.name/~joey/blog/entry/ls:_the_missing_options/

(Well, actually, I never got around to writing -z, but it's clear what it should do, and any ls hackers are encouraged to finish that up.)

haldean• 14 years ago

Your link is broken, FYI

alexpeattie• 14 years ago

I think it should be: http://joeyh.name/blog/entry/ls:_the_missing_options/

al1x• 14 years ago

gobble.wa@gmail.com made a similar post to the freebsd-questions mailing list a month ago. In his case the question was how to print an md5sum along with the file names in a given directory. I saved it because I thought it was a clever hack.

http://lists.freebsd.org/pipermail/freebsd-questions/2012-Se...

A lot of times I catch myself in the mindset of taking a step back and saying "here are the set of tools I have at hand to accomplish a task" without realizing that I should simultaneously be taking a step "in"--so to speak--and acknowledging that the tools I have to work with are not immutable tools cast of iron; they are malleable and can be re-tooled to suit my purposes.. and that sometimes going that route can be the simplest--and in fact "best"--solution.

jtgeibel• 14 years ago

For such large numbers, would it make more sense to use groups of 6 instead of 3? This would allow you to easily identify the megabyte position with the next separator at the terabyte position.

rcthompson• 14 years ago

Here's a wrapper I wrote for ls a while ago that allows you to spell "--color" as "--colour":

http://ubuntuforums.org/showthread.php?t=684239

njharman• 14 years ago

Man, this sounds like every change I try to make to "legacy" code. There's so much debt and smell. I find it very, very hard to leave alone.

meyering• 14 years ago

FYI, there is no need to change GNU ls to get that behavior. You can make it use your locale's separator with either the --block-size="'1" option or by setting the LS_BLOCK_SIZE envvar to that same string:

    $ LC_ALL=en_US.UTF8 ls -og --block-size="'1" .
    -rw-------. 1 5,145,416 Oct  5 16:44 A
    -rw-------. 1 5,137,692 Oct  4 14:37 B
    -rw-------. 1 5,147,168 Oct  8 07:52 C

This feature is documented in the "Block size" section of the coreutils manual: i.e., you can type this to see it:

    info coreutils 'block size'

Hacking ls -l

Related Stories