4 ms·

Or just learn the right method to do that and use `readlink` or `realpath` or similar solution.

robinhouston 7y ago
That’s a very Linux-centric view. Neither of these works on BSD. It’s probably fine if you’re writing scripts that only need to run on Linux, but I wouldn’t call it the “right method”.
- jsjohnst 7y ago
  Readlink is available on FreeBSD, OpenBSD, and NetBSD. https://www.freebsd.org/cgi/man.cgi?query=readlink&sektion=1 https://www.freebsd.org/cgi/man.cgi?query=readlink&sektion=1 So how is that a Linux-centric view again?
  - robinhouston 7y ago
    Sure, readlink exists. And it lets you read symlinks. But it can’t be used to convert relative to absolute directory paths, which I thought was the use you were proposing.
    - jsjohnst 7y ago
      From the man page: > if the -f option is specified, the output is canonicalized by following every symlink in every component of the given path recursively. readlink will resolve both absolute and relative paths, and return the absolute pathname corresponding to file. In this case, the argument does not need to be a symbolic link. This is the case for *BSD, GNU/Linux, and Irix. If macOS would prioritize being consistent with the other Nix OSs, it would be supported too, but alas Apple doesn’t.
stephenr 7y ago
Neither of those is portable, they can't be used in POSIX shell.
- jsjohnst 7y ago
  Neither is GP’s solution portable either.
  - stephenr 7y ago
    `$()` `cd` and `pwd -P` are all part of the POSIX spec. While that doesn't guarantee they're implemented in all shells, it's a lot more likely than things like readlink which are known to not be portable with the flags required to resolve a symlink.
    - jsjohnst 7y ago
      `readlink -f` while not POSIX proper, works on FreeBSD, OpenBSD, NetBSD, and most Linux distros. If you really need to support a wider range than that, reality says you will likely have conditional OS checks in your script anyway, so I’m not sure your point other than being pedantic?
      - stephenr 7y ago
        `readlink -f` on GNU canonicalises the path. `readlink -f` on a *BSD is for formatting the output `readlink -f` on macOS throws an error because it's an supported option.
        jsjohnst 7y ago
        From the FreeBSD man page [0] on readlink: > if the -f option is specified, the output is canonicalized by following every symlink in every component of the given path recursively. readlink will resolve both absolute and relative paths, and return the absolute pathname corresponding to file. In this case, the argument does not need to be a symbolic link. [0] https://www.freebsd.org/cgi/man.cgi?query=readlink&sektion=1 https://www.freebsd.org/cgi/man.cgi?query=readlink&sektion=1 Update: And here’s the OpenBSD man page from 1997 refuting your claim it’s for formatting as well: https://man.openbsd.org/OpenBSD-2.2/readlink.1 https://man.openbsd.org/OpenBSD-2.2/readlink.1 Update 2: OpenBSD (1997): http://www.openbsd.org/cgi-bin/cvsweb/src/usr.bin/readlink/readlink.c?rev=1.10 http://www.openbsd.org/cgi-bin/cvsweb/src/usr.bin/readlink/r... GNU/Linux (2003): https://lists.gnu.org/archive/html/bug-gnu-utils/2003-02/msg00008.html https://lists.gnu.org/archive/html/bug-gnu-utils/2003-02/msg... So it definitely did exist in at least one *BSD before Linux.

That’s a very Linux-centric view. Neither of these works on BSD. It’s probably fine if you’re writing scripts that only need to run on Linux, but I wouldn’t call it the “right method”.

jsjohnst 7y ago
Readlink is available on FreeBSD, OpenBSD, and NetBSD. https://www.freebsd.org/cgi/man.cgi?query=readlink&sektion=1 https://www.freebsd.org/cgi/man.cgi?query=readlink&sektion=1 So how is that a Linux-centric view again?
- robinhouston 7y ago
  Sure, readlink exists. And it lets you read symlinks. But it can’t be used to convert relative to absolute directory paths, which I thought was the use you were proposing.
  - jsjohnst 7y ago
    From the man page: > if the -f option is specified, the output is canonicalized by following every symlink in every component of the given path recursively. readlink will resolve both absolute and relative paths, and return the absolute pathname corresponding to file. In this case, the argument does not need to be a symbolic link. This is the case for *BSD, GNU/Linux, and Irix. If macOS would prioritize being consistent with the other Nix OSs, it would be supported too, but alas Apple doesn’t.

stephenr 7y ago

Neither of those is portable, they can't be used in POSIX shell.

jsjohnst 7y ago
Neither is GP’s solution portable either.
- stephenr 7y ago
  `$()` `cd` and `pwd -P` are all part of the POSIX spec. While that doesn't guarantee they're implemented in all shells, it's a lot more likely than things like readlink which are known to not be portable with the flags required to resolve a symlink.
  - jsjohnst 7y ago
    `readlink -f` while not POSIX proper, works on FreeBSD, OpenBSD, NetBSD, and most Linux distros. If you really need to support a wider range than that, reality says you will likely have conditional OS checks in your script anyway, so I’m not sure your point other than being pedantic?
    - stephenr 7y ago
      `readlink -f` on GNU canonicalises the path. `readlink -f` on a *BSD is for formatting the output `readlink -f` on macOS throws an error because it's an supported option.
      - jsjohnst 7y ago
        From the FreeBSD man page [0] on readlink: > if the -f option is specified, the output is canonicalized by following every symlink in every component of the given path recursively. readlink will resolve both absolute and relative paths, and return the absolute pathname corresponding to file. In this case, the argument does not need to be a symbolic link. [0] https://www.freebsd.org/cgi/man.cgi?query=readlink&sektion=1 https://www.freebsd.org/cgi/man.cgi?query=readlink&sektion=1 Update: And here’s the OpenBSD man page from 1997 refuting your claim it’s for formatting as well: https://man.openbsd.org/OpenBSD-2.2/readlink.1 https://man.openbsd.org/OpenBSD-2.2/readlink.1 Update 2: OpenBSD (1997): http://www.openbsd.org/cgi-bin/cvsweb/src/usr.bin/readlink/readlink.c?rev=1.10 http://www.openbsd.org/cgi-bin/cvsweb/src/usr.bin/readlink/r... GNU/Linux (2003): https://lists.gnu.org/archive/html/bug-gnu-utils/2003-02/msg00008.html https://lists.gnu.org/archive/html/bug-gnu-utils/2003-02/msg... So it definitely did exist in at least one *BSD before Linux.