4 ms·

Don’t forget mktmp for making temporary files or directories, instead of putting files in a set place in /tmp. https://linux.die.net/man/1/mktemp https://linux

by bonyt 7y ago

Don’t forget mktmp for making temporary files or directories, instead of putting files in a set place in /tmp. https://linux.die.net/man/1/mktemp https://linux.die.net/man/1/mktemp

arendtio 7y ago
Well, sadly mktemp is not part of POSIX. So while it is available on a wide range of systems, there are also different implementations with different options. So while I like the job it does, I am also pretty disappointed how 'unportable' scripts become as soon as they use mktemp :-/
- achamayou 7y ago
  And anyway you really want mkstemp ;)
  - faho 7y ago
    Not in a shell. There is no `mkstemp` command, at least on a typical GNU system. There is a `mktemp`, which may very well use the `mkstemp` function in its source. I.e. this is about `mktemp(1)`, not `mktemp(3)`.
- slrz 7y ago
  You can invoke mktemp(1) in ways that work across most contemporary systems. At least if you don't care that the resulting names are going to look a bit weird (have lots of XXXXXX in them due to name prefix vs. template differences among implementations).
  - arendtio 7y ago
    Actually, I am not sure if that is true. I have no example at hand (I could look it up, if you are interested), but a few months ago I was trying hard to create a folder with mktemp using the same command for Linux, MacOS and Android, and as far as I remember, that wasn't as easy as it is supposed to be.
    - slrz 7y ago
      Shouldn't mktemp -d -t name.XXXXXX do it? Possibly in combination with setting TMPDIR if you want to create the directory somewhere else than within the default temp directory. Works with GNU mktemp, the old BSD variant on macOS and also Busybox. Current Android uses Toybox, I think? Its mktemp implementation looks like it takes the same flags as Busybox mktemp. https://landley.net/toybox/help.html#mktemp https://landley.net/toybox/help.html#mktemp
      - arendtio 7y ago
        Well, at least on my Android 7.1.2 (toybox --version 0.7.1-3125af0e06f4-android) mktemp doesn't recognize the -t option (https://github.com/landley/toybox/blob/0.7.1/toys/lsb/mktemp.c https://github.com/landley/toybox/blob/0.7.1/toys/lsb/mktemp...). So it seems to be fixed in newer versions, but I am sure there will be some installations with the old versions around for a while. Instead, I could use --tmpdir, but somehow that one seems to be buggy: $ mktemp -d --tmpdir name.XXXXXX mktemp: Failed to create directory name.XXXXXX/name.XXXXXX/tmp.sL2WbI: No such file or directory The macOS version, on the other hand, does work with those options, but it creates a file like name.XXXXXX.veCNnwkX (instead of name.veCNnwkX) so not a deal-breaker, but it is certainly not what you would have expected. And using --tmpdir with macOS doesn't work either. So yes, in theory, it shouldn't be too hard but sadly, the reality is often buggy and outdated :-/
- posix_me_less 7y ago
  It is sad to read these comments by people believing POSIX is something relevant today. My advice is to give up on false hope that POSIX will solve portability problems. POSIX ideas of shell are 30 years old and refusing to use anything newer alone won't make your script work correctly on all systems. If feasible, install bash, which has become the standard de facto. Or just write your script to test for the shell version and then launch appropriate code path.
  - arendtio 7y ago
    I know that POSIX doesn't meet the expectations many of us have, but I don't see how it isn't relevant anymore? I mean, if you want to write portable shell scripts it is still a good reference on what you can expect to find on many systems (and which are options introduce by GNU and the likes). Yes, ultimately you have to test your scripts on the actual systems, but that is something you have to do anyway. For example, when you run scripts on MacOS and you run into old Bash bugs because Apple refuses to ship an up-to-date version, those are issues a standard can't solve. However, I have no experience how much you can count on POSIX when it comes to C APIs and the like.
    - posix_me_less 7y ago
      POSIX is part of unix history and running systems have some compatibility level with it, so in that respect it is relevant. But as for writing universally working scripts, it is not a panacea, because systems shells are not exactly POSIX compliant. For example, bash and Linux, the standard of unix de facto, deviate from POSIX, the standard de iure. > but that is something you have to do anyway. Exactly my point.
gabrielblack 7y ago
mktemp couldn't make a script idempotent. I remember a script that failed because it needed to create temporary executables in /tmp. To apply some hardening policies, someone remounted /tmp in "noexec" mode and ... kaboom. So if you use that, better if you specify TMPDIR with proper checking.

by bonyt 7y ago

Don’t forget mktmp for making temporary files or directories, instead of putting files in a set place in /tmp. https://linux.die.net/man/1/mktemp https://linux.die.net/man/1/mktemp

arendtio 7y ago

Well, sadly mktemp is not part of POSIX. So while it is available on a wide range of systems, there are also different implementations with different options. So while I like the job it does, I am also pretty disappointed how 'unportable' scripts become as soon as they use mktemp :-/

achamayou 7y ago
And anyway you really want mkstemp ;)
- faho 7y ago
  Not in a shell. There is no `mkstemp` command, at least on a typical GNU system. There is a `mktemp`, which may very well use the `mkstemp` function in its source. I.e. this is about `mktemp(1)`, not `mktemp(3)`.
slrz 7y ago
You can invoke mktemp(1) in ways that work across most contemporary systems. At least if you don't care that the resulting names are going to look a bit weird (have lots of XXXXXX in them due to name prefix vs. template differences among implementations).
- arendtio 7y ago
  Actually, I am not sure if that is true. I have no example at hand (I could look it up, if you are interested), but a few months ago I was trying hard to create a folder with mktemp using the same command for Linux, MacOS and Android, and as far as I remember, that wasn't as easy as it is supposed to be.
  - slrz 7y ago
    Shouldn't mktemp -d -t name.XXXXXX do it? Possibly in combination with setting TMPDIR if you want to create the directory somewhere else than within the default temp directory. Works with GNU mktemp, the old BSD variant on macOS and also Busybox. Current Android uses Toybox, I think? Its mktemp implementation looks like it takes the same flags as Busybox mktemp. https://landley.net/toybox/help.html#mktemp https://landley.net/toybox/help.html#mktemp
    - arendtio 7y ago
      Well, at least on my Android 7.1.2 (toybox --version 0.7.1-3125af0e06f4-android) mktemp doesn't recognize the -t option (https://github.com/landley/toybox/blob/0.7.1/toys/lsb/mktemp.c https://github.com/landley/toybox/blob/0.7.1/toys/lsb/mktemp...). So it seems to be fixed in newer versions, but I am sure there will be some installations with the old versions around for a while. Instead, I could use --tmpdir, but somehow that one seems to be buggy: $ mktemp -d --tmpdir name.XXXXXX mktemp: Failed to create directory name.XXXXXX/name.XXXXXX/tmp.sL2WbI: No such file or directory The macOS version, on the other hand, does work with those options, but it creates a file like name.XXXXXX.veCNnwkX (instead of name.veCNnwkX) so not a deal-breaker, but it is certainly not what you would have expected. And using --tmpdir with macOS doesn't work either. So yes, in theory, it shouldn't be too hard but sadly, the reality is often buggy and outdated :-/
posix_me_less 7y ago
It is sad to read these comments by people believing POSIX is something relevant today. My advice is to give up on false hope that POSIX will solve portability problems. POSIX ideas of shell are 30 years old and refusing to use anything newer alone won't make your script work correctly on all systems. If feasible, install bash, which has become the standard de facto. Or just write your script to test for the shell version and then launch appropriate code path.
- arendtio 7y ago
  I know that POSIX doesn't meet the expectations many of us have, but I don't see how it isn't relevant anymore? I mean, if you want to write portable shell scripts it is still a good reference on what you can expect to find on many systems (and which are options introduce by GNU and the likes). Yes, ultimately you have to test your scripts on the actual systems, but that is something you have to do anyway. For example, when you run scripts on MacOS and you run into old Bash bugs because Apple refuses to ship an up-to-date version, those are issues a standard can't solve. However, I have no experience how much you can count on POSIX when it comes to C APIs and the like.
  - posix_me_less 7y ago
    POSIX is part of unix history and running systems have some compatibility level with it, so in that respect it is relevant. But as for writing universally working scripts, it is not a panacea, because systems shells are not exactly POSIX compliant. For example, bash and Linux, the standard of unix de facto, deviate from POSIX, the standard de iure. > but that is something you have to do anyway. Exactly my point.

gabrielblack 7y ago

mktemp couldn't make a script idempotent. I remember a script that failed because it needed to create temporary executables in /tmp. To apply some hardening policies, someone remounted /tmp in "noexec" mode and ... kaboom. So if you use that, better if you specify TMPDIR with proper checking.