7 ms·

> Does this mean the smallest /bin/true is actually an empty file? That was exactly the implementation of /bin/true in Unix v7: <https://github.com/v7unix/v7un

> Does this mean the smallest /bin/true is actually an empty file? That was exactly the implementation of /bin/true in Unix v7: <https://github.com/v7unix/v7unix/blob/master/v7/bin/true https://github.com/v7unix/v7unix/blob/master/v7/bin/true>

re 5y ago
This subject has been posted about a few times on HN, along with some looks at the evolution of the implementation of the command: https://hn.algolia.com/?dateRange=all&page=0&prefix=false&query=%22bin%2Ftrue%22&sort=byPopularity&type=story https://hn.algolia.com/?dateRange=all&page=0&prefix=false&qu... Here's the most recent, with the most comments: https://news.ycombinator.com/item?id=28257666 https://news.ycombinator.com/item?id=28257666
aidenn0 5y ago
It also means that the shortest quine is an empty file.
Cloudef 5y ago
Meanwhile GNU coreutils version of /bin/true ... https://github.com/coreutils/coreutils/blob/master/src/true.c https://github.com/coreutils/coreutils/blob/master/src/true....
- mikepurvis 5y ago
  Fair, though most of that is the fact that it has --help output and also that the same source covers both true and false. But yeah.
  - e3bc54b2 5y ago
    IIRC GNU's /bin/true also has massive performance advantage. I am not able to find it presently, but an old post tried to reverse engineer it, and turns out it does caching and whatnot to get something like 12 GBps throughput. Edit: I was wrong, it is actually GNU 'yes': https://www.teddit.net/r/unix/comments/6gxduc/how_is_gnu_yes_so_fast/?st=j3v3iw3c&sh=5651ea3c https://www.teddit.net/r/unix/comments/6gxduc/how_is_gnu_yes...
    - anyfoo 5y ago
      And yet you might still be right: If an empty file gets parsed and executed by the shell[1], the shell's initialization code might make things much slower than a small C program. [1] Which is a valid assumption, as it's often the default (not sure if it's POSIX[2]), e.g. this gets clearly executed by my shell despite not having a shebang or anything else: echo 'echo $SHELL' > /tmp/foo; chmod +x /tmp/foo; /tmp/foo [2] Edit: It is POSIX, I know now because there's a whole subthread about it further down, that even quotes the standard, thanks gnarula.
      - Cloudef 5y ago
        The real reason why things are fast in popular shells is because they implement most of coreutils as builtins. The /bin/true being empty file would prevent it from working when called with exec for example, so that's why we don't use empty files anymore.
      - rrauenza 5y ago
        I was going to see what strace does with an empty /tmp/foo, and it fails: > write(2, "strace: exec: Exec format error\n", 32strace: exec: Exec format error So the empty file is not exec()able. I think it can only be invoked from a shell. subprocess.call("/tmp/foo", shell=xxxx) demonstrates it. I wonder if that was the case for Unix v7 that had it zero length? (...mentioned in another thread.)
        dfox 5y ago
        From quick scan of v7 exec() implementation it seems that it has to be case as getxfile() would return ENOEXEC for files smaller than sizeof(u_exdata) (which is a.out header as C struct).
randombits0 5y ago
It’s also the smallest quine, a program that outputs its own source code.
- anyfoo 5y ago
  And probably the one with the single highest number of programming languages for which it is a valid quine[1].
  - Shared404 5y ago
    You appear to be missing the link, I would quite like to read it however if you get the chance to edit that in!
    - anyfoo 5y ago
      It doesn’t actually support what I said I think, but you might like it anyway: http://www.madore.org/~david/computers/quine.html http://www.madore.org/~david/computers/quine.html
      - k0k0r0 5y ago
        This is worth its own post on HN
        bombcar 5y ago
        https://news.ycombinator.com/item?id=29888887 https://news.ycombinator.com/item?id=29888887
    - ummwhat 5y ago
      He's not missing the link. The link is the empty string.
bodyfour 5y ago
And it's actually pretty clever from a performance point-of-view. You always have to read the inode to determine whether the file is executable. The inode included the locations of the first "direct" blocks of the file's contents. So if the file is empty you know that immediately. If the file even had a single comment line, it would mean having to do a disk seek to read it. So it would effectively double the disk I/O needed to run "/bin/true"
- Dylan16807 5y ago
  Clever yes, but you'll get much bigger benefits if you use a filesystem that can store tiny files inside the inode.
  - deleted 5y ago
    [deleted]
userbinator 5y ago
A more interesting question: Is it copyrightable? I'd say it isn't (and the same goes for false); but whether it's patentable is more debatable.
- 1-more 5y ago
  AT&T and Sun seemed to think so https://sudonull.com/post/143079-Copyright-on-the-bin-true-command https://sudonull.com/post/143079-Copyright-on-the-bin-true-c...

re 5y ago

This subject has been posted about a few times on HN, along with some looks at the evolution of the implementation of the command: https://hn.algolia.com/?dateRange=all&page=0&prefix=false&query=%22bin%2Ftrue%22&sort=byPopularity&type=story https://hn.algolia.com/?dateRange=all&page=0&prefix=false&qu... Here's the most recent, with the most comments: https://news.ycombinator.com/item?id=28257666 https://news.ycombinator.com/item?id=28257666

aidenn0 5y ago

It also means that the shortest quine is an empty file.

Cloudef 5y ago

Meanwhile GNU coreutils version of /bin/true ... https://github.com/coreutils/coreutils/blob/master/src/true.c https://github.com/coreutils/coreutils/blob/master/src/true....

mikepurvis 5y ago
Fair, though most of that is the fact that it has --help output and also that the same source covers both true and false. But yeah.
- e3bc54b2 5y ago
  IIRC GNU's /bin/true also has massive performance advantage. I am not able to find it presently, but an old post tried to reverse engineer it, and turns out it does caching and whatnot to get something like 12 GBps throughput. Edit: I was wrong, it is actually GNU 'yes': https://www.teddit.net/r/unix/comments/6gxduc/how_is_gnu_yes_so_fast/?st=j3v3iw3c&sh=5651ea3c https://www.teddit.net/r/unix/comments/6gxduc/how_is_gnu_yes...
  - anyfoo 5y ago
    And yet you might still be right: If an empty file gets parsed and executed by the shell[1], the shell's initialization code might make things much slower than a small C program. [1] Which is a valid assumption, as it's often the default (not sure if it's POSIX[2]), e.g. this gets clearly executed by my shell despite not having a shebang or anything else: echo 'echo $SHELL' > /tmp/foo; chmod +x /tmp/foo; /tmp/foo [2] Edit: It is POSIX, I know now because there's a whole subthread about it further down, that even quotes the standard, thanks gnarula.
    - Cloudef 5y ago
      The real reason why things are fast in popular shells is because they implement most of coreutils as builtins. The /bin/true being empty file would prevent it from working when called with exec for example, so that's why we don't use empty files anymore.
    - rrauenza 5y ago
      I was going to see what strace does with an empty /tmp/foo, and it fails: > write(2, "strace: exec: Exec format error\n", 32strace: exec: Exec format error So the empty file is not exec()able. I think it can only be invoked from a shell. subprocess.call("/tmp/foo", shell=xxxx) demonstrates it. I wonder if that was the case for Unix v7 that had it zero length? (...mentioned in another thread.)
      - dfox 5y ago
        From quick scan of v7 exec() implementation it seems that it has to be case as getxfile() would return ENOEXEC for files smaller than sizeof(u_exdata) (which is a.out header as C struct).

randombits0 5y ago

It’s also the smallest quine, a program that outputs its own source code.

anyfoo 5y ago
And probably the one with the single highest number of programming languages for which it is a valid quine[1].
- Shared404 5y ago
  You appear to be missing the link, I would quite like to read it however if you get the chance to edit that in!
  - anyfoo 5y ago
    It doesn’t actually support what I said I think, but you might like it anyway: http://www.madore.org/~david/computers/quine.html http://www.madore.org/~david/computers/quine.html
    - k0k0r0 5y ago
      This is worth its own post on HN
      - bombcar 5y ago
        https://news.ycombinator.com/item?id=29888887 https://news.ycombinator.com/item?id=29888887
  - ummwhat 5y ago
    He's not missing the link. The link is the empty string.

bodyfour 5y ago

And it's actually pretty clever from a performance point-of-view. You always have to read the inode to determine whether the file is executable. The inode included the locations of the first "direct" blocks of the file's contents. So if the file is empty you know that immediately. If the file even had a single comment line, it would mean having to do a disk seek to read it. So it would effectively double the disk I/O needed to run "/bin/true"

Dylan16807 5y ago
Clever yes, but you'll get much bigger benefits if you use a filesystem that can store tiny files inside the inode.
- deleted 5y ago
  [deleted]

userbinator 5y ago

A more interesting question: Is it copyrightable? I'd say it isn't (and the same goes for false); but whether it's patentable is more debatable.

1-more 5y ago
AT&T and Sun seemed to think so https://sudonull.com/post/143079-Copyright-on-the-bin-true-command https://sudonull.com/post/143079-Copyright-on-the-bin-true-c...