[OT] 'perl' is not the 'perl' reported by 'which perl'

syphilis has asked for the wisdom of the Perl Monks concerning the following question:

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Re: [OT] 'perl' is not the 'perl' reported by 'which perl' by jo37 (Curate) on Aug 21, 2020 at 15:01 UTC
This might be caused by bash's hashing. Like this: jo@bear$ PATH=/home/jo/bin:/usr/local/bin:/usr/bin:/bin jo@bear$ cat <<EOF >tellme.sh > #!/bin/bash > echo this is tellme.sh from /usr/local/bin > EOF jo@bear$ chmod +x tellme.sh jo@bear$ sudo cp tellme.sh /usr/local/bin jo@bear$ which tellme.sh /usr/local/bin/tellme.sh jo@bear$ tellme.sh this is tellme.sh from /usr/local/bin jo@bear$ cat <<EOF >tellme.sh > #!/bin/bash > echo this is tellme.sh from ~/bin EOF jo@bear$ cp tellme.sh bin jo@bear$ which tellme.sh /home/jo/bin/tellme.sh jo@bear$ tellme.sh this is tellme.sh from /usr/local/bin jo@bear$ hash -d tellme.sh jo@bear$ tellme.sh this is tellme.sh from /home/jo/bin [download] Greetings, -jo `$gryYup$d0ylprbpriprrYpkJl2xyl~rzg??P~5lp2hyl0p$`	[reply] [d/l]
Re^2:[OT] 'perl' is not the 'perl' reported by 'which perl' by LanX (Saint) on Aug 21, 2020 at 17:46 UTC
"Interesting" feature... This link might be useful for the OP, especially the `type` command and other fixes: https://unix.stackexchange.com/questions/5609/how-do-i-clear-bashs-cache-of-paths-to-executables#5610 Cheers Rolf _{(addicted to the Perl Programming Language :) Wikisyntax for the Monastery}	[reply] [d/l]
Re^3: [OT] 'perl' is not the 'perl' reported by 'which perl' (which vs type References) by eyepopslikeamosquito (Archbishop) on Aug 21, 2020 at 22:38 UTC
This link might be useful for the OP, especially the `type` command Ha ha, over twenty years ago I was ordered by our Unix guru at work to never use the C shell and to "always use the `type` command, never the `which` command". Being frightened of our Unix guru, I've always followed that advice ... but been surprised many times over the years by folks looking over my shoulder asking "what is the `type` command?" - my experience has been that most people use the `which` command and have never even heard of the `type` command! ... perhaps showing the importance of a descriptive name. See also: why not use which and what to use instead (stackexchange, where the `which` command is discouraged) how is whence different than which (stackexchange question) cd external command (stackexchange question) What is the Unix command to found out what executable file corresponds to (superuser question) Csh considered harmful by Tom Christiansen (1995) References Added Later Unix type command (wikipedia) Unix which command (wikipedia) POSIX command command (sic) (wikipedia) KornShell (wikipedia) POSIX type command (opengroup) Linux type command (linuxcommand) POSIX command command (sic) (opengroup) KornShell whence command (mks) Re^5: Devel::NYTProf: "undefined symbol: PL_stack_sp" error by ikegami (2021) Re^9: Devel::NYTProf: "undefined symbol: PL_stack_sp" error by me (2021) (Windows) verbatim command line arguments inside Perl script by LanX (2021) $^O empty in windows powershell by WithABeard (2022) What is Windows equivalent of the which command in Unix? Is there an equivalent PowerShell command? Windows Powershell Get-Command See Also Re: Some Help for a Report About Perl (One-liner References)	[reply] [d/l] [select]
Re^4: [OT] 'perl' is not the 'perl' reported by 'which perl' by kcott (Archbishop) on Aug 22, 2020 at 01:55 UTC
Re^4: [OT] 'perl' is not the 'perl' reported by 'which perl' by trippledubs (Deacon) on Aug 24, 2020 at 01:39 UTC
Re: [OT] 'perl' is not the 'perl' reported by 'which perl' by LanX (Saint) on Aug 21, 2020 at 14:16 UTC
Did you check if there are any aliases in bash? What happens if you try to call Perl from Perl via qx? Cheers Rolf _{(addicted to the Perl Programming Language :) Wikisyntax for the Monastery}	[reply]
Re^2: [OT] 'perl' is not the 'perl' reported by 'which perl' by perlfan (Parson) on Aug 21, 2020 at 15:46 UTC
`alias` is a good thing to check (`alias -p`). Similarly, a bash function `perl` defined in your environment could cause a similar effect and are not reported by `alias -p`. If that's not expected and it exists, then something fish is happening for sure. I don't know off the top of my head how to see what bash functions are currently defined. I believe `which` is aware of aliases, not sure about bash functions. Does `which which` what you expect? Maybe try it with the absolute path.	[reply] [d/l] [select]
Re: [OT] 'perl' is not the 'perl' reported by 'which perl' by syphilis (Archbishop) on Aug 22, 2020 at 05:36 UTC
On Ubuntu-18.04.5 the manual (`man which`) states: `DESCRIPTION which returns the pathnames of the files (or links) which would be exe +- cuted in the current environment, had its arguments been given as com +- mands in a strictly POSIX-conformant shell. It does this by searchin +g the PATH for executable files matching the names of the arguments. I +t does not canonicalize path names.` [download] I assume that I have a POSIX-conformant shell: `$ echo $SHELL /bin/bash` [download] I don't know what "It does not canonicalize path names" means. Is that relevant to this issue ? Pretty clearly, the manual tells me that `which perl` returns the path of the perl that will be executed when, in my bash shell, I enter a command beginning with the word "perl". Just as clearly, that assertion is false in my particular situation. Here's a demo, starting with a freshly opened bash shell: $ echo $PATH /usr/local/sbin:/usr/local/bin:/usr/sbin:/usr/bin:/sbin:/bin:/usr/game +s:/usr/local/games:/snap/bin $ which perl /usr/bin/perl $ perl -le 'print $];' 5.026001 $ /usr/bin/perl -le 'print $];' 5.026001 # Select another perl, and hide the # perl executable by renaming it $ mv ~/perl528-d/bin/perl ~/perl528-d/bin/perl_hide # Prepend the location of that # "hidden" perl to $PATH $ export PATH=~/perl528-d/bin:$PATH # That change to $PATH clears the cache, # so run a perl command that will again # set the cached perl to /usr/bin/perl. # The problem does not arise if this # step is omitted. $ perl -le 'print $];' 5.026001 # Make the hidden perl visible again $ mv ~/perl528-d/bin/perl_hide ~/perl528-d/bin/perl $ which perl /home/sisyphus/perl528-d/bin/perl $ /home/sisyphus/perl528-d/bin/perl -le 'print $];' 5.028000 $ perl -le 'print $];' 5.026001 [download] The only thing happening that's "wrong" is that final output. Everything else is sane and as expected. Of course, in my original case, I didn't run a command aimed at caching perl to /usr/bin/perl. (I just ran `perl -V`, expecting to see the configuration of the newly installed 5.33.1 - and getting the configuration of the system perl instead.) And I didn't begin by renaming the "perl" executable to something else. It was installed already named as something else (namely "perl5.33.1"). All I did was to rename "perl5.33.1" to "perl" - which would have been sufficient if "perl" was not by then cached as "/usr/bin/perl" I do think the "which" documentation is way too glib. Sure, it specifies the way that "which" determines the pathname of its argument(s), but it should not be unconditionally asserting that this will match the pathname used when that argument is given as a command in a strictly POSIX-conformant shell. That is (demonstrably) not always true - and the documentation should at least point this out. Cheers, Rob PS Following on from where I left off the above one liners, and just to demonstrate clearly that a change to $PATH is enough to reset the cache: `$ perl -le 'print $];' 5.026001 $ export PATH=~/nonexistent:$PATH $ perl -le 'print $];' 5.028000` [download] But I doubt that needed to be demonstrated, anyway ;-)	[reply] [d/l] [select]
Re^2: [OT] 'perl' is not the 'perl' reported by 'which perl' by LanX (Saint) on Aug 22, 2020 at 14:23 UTC
I think the excellent links provided in Re^3: [OT] 'perl' is not the 'perl' reported by 'which perl' (which vs type References) explain why. In short: `which` was invented as an executable for csh , but bash later implemented `type` as proper built-in. In other words "which" is an alien to bash's logic. Cheers Rolf _{(addicted to the Perl Programming Language :) Wikisyntax for the Monastery}	[reply] [d/l] [select]
Re^2: [OT] 'perl' is not the 'perl' reported by 'which perl' by Anonymous Monk on Aug 22, 2020 at 07:40 UTC
You seem to have figured out that the issue here is bash's hashing. You can delete the entire hash with `hash -r` or just the one path with `hash -d perl`. which(1) can be pretty squirrelly and and should be avoided. Bash has the `type` builtin which will display aliases as well as executable files. To get the documentation on bash builtins, you can use the help builtin. e.g. `help type` Canonical names aren't an issue here but realpath is how you get one.	[reply] [d/l] [select]
Re^3: [OT] 'perl' is not the 'perl' reported by 'which perl' by syphilis (Archbishop) on Aug 22, 2020 at 11:38 UTC
which(1) can be pretty squirrelly and and should be avoided. Yes - but the main problem with it is simply that its documentation misses out on some crucial detail. If that documentation (as provided by `man which`) mentioned that it didn't always provide what the current documentation (as provided by `man which`) states that it does, then you could not be critical of it. Even better if that documentation recommended using "type" instead. But I find it a bit laughable that you have to do `type perl` in order to get the information that `man which` falsely claims as being always returned by `which perl` Anyway ... thanks (as always) to all respondents for their contributions. And, in future, whenever I see anyone on perlmonks respond to a question with "`which perl` ?" I'll personally set them straight ;-) Cheers, Rob	[reply] [d/l] [select]
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