Expansion of $0 changed in 3.5.0 release even for bash scripts

[vlitvin]

Expansion of $0 differs from one in bash and zsh in script, even when shell explicitly set with shebang. My test show that this behaviour changed in 3.5.0 resulting in broken bash scripts.

Fish version:

  fish --version
  fish, version 3.5.1

System version:

$ uname -a
Darwin XXXXX-MacBook-Pro.local 21.3.0 Darwin Kernel Version 21.3.0: Wed Jan  5 21:37:58 PST 2022; root:xnu-8019.80.24~20/RELEASE_X86_64 x86_64
$ echo $TERM
xterm-256color

I've tried sh -c 'env HOME=$(mktemp -d) fish' and got same results

Steps to reproduce:

# Create simple bash script
echo <<EOF > ./expansion.sh
#!/usr/bin/env bash

echo $0
EOF

# Make it executable
chmod +x ./expansion.sh

# Observe different output
./expansion.sh
<absolute_path>/expansion.sh

bash ./expansion.sh
./expansion.sh

zsh ./expansion.sh
./expansion.sh

I know that compatability with other shells not guaranteed, but it would be nice to have at least clear statement about it in changelog.
Though, it's not crystal clear to me, why behaviour differs even with shebang.

[faho]

Bisects to ed78fd2.

Note:

t this behaviour changed in 3.5.0 resulting in broken bash scripts.

If your bash script is "broken" by this, it is already broken. $0 can always be absolute. Call $PWD/expansion.sh in bash, and it will be absolute. Call it as e.g. /path/to/script/expansion.sh from elsewhere, and it'll be absolute.

$0 is one of those brilliant unix features that appear to be nice and simple until you figure out they aren't. $0 can be any relative or absolute path to your script - unless you tell the shell to use another value:

bash -c '. ./expansion.sh' /bin/grep

Now your script thinks it is /bin/grep in bash and dash, but './expansion.sh' in zsh.

---

I'd probably lean towards changing this back because it wasn't supposed to be changed, but your use of $0 isn't actually any good, and it's not like we pass any arbitrary value here. It's a perfectly cromulent path to the script.

[vlitvin]

I've got your point. My bash scripts will fail in certain circumstances depending on how I invoke them.

Thanks you for fix.