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Comment by yjftsjthsd-h | Hacker News Reader

That's a portable sh solution, isn't it? Like, yes, it does work on FreeBSD, but it isn't exclusive

The portablest solution I have found is:

    rundir=$(cd -P -- "$(dirname -- "$0")" && printf '%s\n' "$(pwd -P)")

This isn't a portable solution at all because it doesn't solve the problem of the script being symlinked. While it does resolve directory symlilnks, that part is usually not even needed as finding a helper works just as well with a symlink to the directory containing the script as it does with the resolved directory. What doesn't work is a directory containing a symlink to the script which your "solution" fails to resolve.

Additionally (and the article doesn't solve this either), when invoked through $PATH, $0 will not be a full path but only the name of the command. In that case you want to start with "$(command -v "$0")" instead of just "$0".

No, $0 is a full path when invoked via $PATH.

I'm curious: why the `printf '%s\n' "$(pwd -P)"` ? wouldn't just `pwd -P` achieve the same?

Actually nothing. The format seems to have come from a similar line that builds the script path..

    printf '%s/%s\n' "$(pwd -P)" "$(basename "$0")"

It's just been in place, in so many places, so long it's become unquestionable. So yes the `pwd -P` in this case will suffice.

I've been using just `V="$(cd -- "$(dirname -- "$0")"; pwd)"` for ages, everything quoted, several OSs, never had an issue with the output that required me to format it again.

This approach breaks if you run the script from a symlink.

I think the closest portable solution we have would be basename instead of realpath, but I don't think that takes care of the symlink problem described in the article.

POSIX has no realpath(1), so no.

*Yet.

Will be added in the upcoming revision: https://www.austingroupbugs.net/view.php?id=1457

20 years ago it was a "BSD thing", but it seems to be more wide-spread these days; even my Alpine busybox system has it. I'm sure there are some platforms without it, but there are also platforms without some POSIX tools – it's never a guarantee.

All the main platforms have realpath(1). It was added to GNU Linux over 10 years ago now, to aid portability, and be a more natural command to access this functionality than readlink(1)

Saw a comment on another site mention this, but NetBSD won't get it until 10.0 (not yet released) and OpenBSD got it in 7.1 (released last year). Of course I'm of the mindset that building complex shell scripts is simply an exercise in masochism so this all seems like a solution in search of a problem.

Not really. macOS until version 12 doesn’t have realpath(1), it was only added this year. You can’t rely on it for portable code.

To clarify, it was added (late) last year, with macos 13 (Ventura).

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