Feature #16952: Kernel.exec gives an incorrect error message when passed a script with a non-existing shebang

• Status: Open
• Priority: Normal
• Assignee: -
• Target version: -

[deivid (David Rodríguez)]

$ cat myscript.rb 
#!/bad/ruby/shebang

puts "Hei!"

$ ruby -e 'Kernel.exec("myscript.rb")'

Traceback (most recent call last):
    1: from -e:1:in `<main>'
-e:1:in `exec': No such file or directory - myscript.rb (Errno::ENOENT)

From the error, I understand that the script is not there, but the script is clearly there.

I would've expected something more similar to what you get if you try to run the script directly from the shell:

$ ./myscript.rb 
bash: ./myscript.rb: /bad/ruby/shebang: bad interpreter: No such file or directory

[Eregon (Benoit Daloze)]

I would think this is just the errno you get from execve(2).
Ruby itself doesn't try to read the shebang.

So not sure Ruby can do much here.
man execve on Linux says:

ENOENT The file pathname or a script or ELF interpreter does not exist, or a shared library needed for the file or interpreter cannot be found.

OTOH I think Bash has its own handling and actually reads the shebang (I'm not sure why, and it makes it all more confusing).

[jeremyevans0 (Jeremy Evans)]

• Backport deleted (2.5: UNKNOWN, 2.6: UNKNOWN, 2.7: UNKNOWN)
• ruby -v deleted (ruby 2.7.1p83 (2020-03-31 revision a0c7c23c9c) [x86_64-linux])
• Tracker changed from Bug to Feature

When I run your example in my shell (OpenBSD ksh), I get:

$ ./myscript.rb
ksh: ./myscript.rb: No such file or directory
$ ruby -e 'Kernel.exec("myscript.rb")'
Traceback (most recent call last):
        1: from -e:1:in `<main>'
-e:1:in `exec': No such file or directory - myscript.rb (Errno::ENOENT)

Eregon (Benoit Daloze) is correct, examining the shebang appears to be a bash-specific behavior, not a general behavior. So I don't think this qualifies as a bug in Ruby. It could potentially be a useful feature, though.

[deivid (David Rodríguez)]

In my opinion, the error message I'm being given is a bug, because it's telling me that a file that does exist, doesn't exist. Ruby should double check if the file exists before giving that error message, and if it does exist, give a more generic message that it's not clearly incorrect.