Which is not Posix
hynek.me
Which is not Posix
1–10 of 97 posts
Re: Which is not Posix
#2Yeah, no thanks, I'm going to keep using `which`, and distributions are going to support it, no matter how "standard" `command -v` is. The only reason we're talking about this is that it's so noteworthy that any distro would seriously suggest people avoid `which`, which is the de facto standard.
Re: Which is not Posix
#3macOS Catalina 10.15.7
$ command -v command
command
$ which command
/usr/bin/commandRe: Which is not Posix
#4macOS Catalina 10.15.7 $ command -v command command vs $ which command /usr/bin/command
command is a bash builtin. /usr/bin/command is a bash script that calls into the builtin command.
If you just run `command`, you are running the builtin function and not the /usr/bin/command file.
Try running `command -V command` and `command -V /usr/bin/command`
Re: Which is not Posix
#5Yeah, no thanks, I'm going to keep using `which`, and distributions are going to support it, no matter how "standard" `command -v` is. The only reason we're talking about this is that it's so noteworthy that any distro would seriously suggest people avoid `which`, which is the de facto standard.
Busybox also supports both variants, which is nice.
C:\Users\luser>busybox64 sh
~ $ command -v ssh
C:/WINDOWS/System32/OpenSSH/ssh.exe
~ $ which ssh
C:/WINDOWS/System32/OpenSSH/ssh.exe
~ $ exitRe: Which is not Posix
#6I do not understand this Debian 'which' kerfuffle, but seems a big argument over nothing.
But for me, 'type' is my go to in scripts. And as a tcsh user, I never knew 'which' was a thing in Bourne shells until I checked a few minutes ago. I do not know when it appeared, but I thought in the 'old days' 'which' was specific just to [t]csh.
Also, I never heard of 'command -v' until I saw it in LWN a few days ago :)
Re: Which is not Posix
#7macOS Catalina 10.15.7 $ command -v command command vs $ which command /usr/bin/command
command is a bash builtin. /usr/bin/command is a bash script that calls into the builtin command. If you just run `command`, you are running the builtin function and not the /usr/bin/command file. Try running `command -V command` and `command -V /usr/bin/command`
Point being, it doesn't help you finding /usr/bin/command via regular search in PATH and it reports the builtin instead.
Re: Which is not Posix
#8Not sure why the outcome of "`which` is not POSIX" would be "essentially everybody should stop using `which` and start using `command -v`, which is poorly known, has different semantics, and is covered in relatively little introductory material" rather than "this is just another example of why POSIX has been nearly irrelevant for a long time now".
systemd is not POSIX, either, but that's not taken as some justification for removing it from Debian – this whole drama is just pointless pedantry over something precisely because it is so low stakes.
Re: Which is not Posix
#9Based on the title I was thinking this was a quiz. I am imagining a game where it shows two shell snippets and you need to select the one that works correctly under a strict POSIX environment.
Re: Which is not Posix
#10OK, I don't get `command`. When I run `command time -v sleep 10` it clearly runs /usr/bin/time on my system (the bash builtin doesn't have the -v option), but if I run `command -v time` it outputs `time`, corresponding to the builtin. How is this helpful? Also shouldn't `command` and `command -v` find the same things?
edit: Well apparently this is the standard behavior [1]. So lookup is not the same for `command ` vs `command -v `, and there doesn't seem to be a standard way to lookup the executable started by `command `. `which` seem to fill that gap.
[1] https://pubs.opengroup.org/onlinepubs/007904975/utilities/co...