Set argv0= to allow multi-executable binaries

[matthewbauer]

Some binaries use $0 sniffing to determine what mode to use. So, we
want to propagate the argv0 we are using so we can use these programs.

A good example is “coreutils” which uses this method:

$ tree /nix/store/...-coreutils-8.31
.
├── bin
│   ├── [ -> coreutils
│   ├── b2sum -> coreutils
│   ├── base32 -> coreutils
│   ├── base64 -> coreutils
│   ├── basename -> coreutils
│   ├── basenc -> coreutils
│   ├── cat -> coreutils
│   ├── chcon -> coreutils
│   ├── chgrp -> coreutils
│   ├── chmod -> coreutils
│   ├── chown -> coreutils
│   ├── chroot -> coreutils
│   ├── cksum -> coreutils
│   ├── comm -> coreutils
│   ├── coreutils
│   ├── cp -> coreutils
│   ├── csplit -> coreutils
│   ├── cut -> coreutils
│   ├── date -> coreutils
│   ├── dd -> coreutils
│   ├── df -> coreutils
│   ├── dir -> coreutils
│   ├── dircolors -> coreutils
│   ├── dirname -> coreutils
│   ├── du -> coreutils
│   ├── echo -> coreutils
│   ├── env -> coreutils
│   ├── expand -> coreutils
│   ├── expr -> coreutils
│   ├── factor -> coreutils
│   ├── false -> coreutils
│   ├── fmt -> coreutils
│   ├── fold -> coreutils
│   ├── groups -> coreutils
│   ├── head -> coreutils
│   ├── hostid -> coreutils
│   ├── id -> coreutils
│   ├── install -> coreutils
│   ├── join -> coreutils
│   ├── kill -> coreutils
│   ├── link -> coreutils
│   ├── ln -> coreutils
│   ├── logname -> coreutils
│   ├── ls -> coreutils
│   ├── md5sum -> coreutils
│   ├── mkdir -> coreutils
│   ├── mkfifo -> coreutils
│   ├── mknod -> coreutils
│   ├── mktemp -> coreutils
│   ├── mv -> coreutils
│   ├── nice -> coreutils
│   ├── nl -> coreutils
│   ├── nohup -> coreutils
│   ├── nproc -> coreutils
│   ├── numfmt -> coreutils
│   ├── od -> coreutils
│   ├── paste -> coreutils
│   ├── pathchk -> coreutils
│   ├── pinky -> coreutils
│   ├── pr -> coreutils
│   ├── printenv -> coreutils
│   ├── printf -> coreutils
│   ├── ptx -> coreutils
│   ├── pwd -> coreutils
│   ├── readlink -> coreutils
│   ├── realpath -> coreutils
│   ├── rm -> coreutils
│   ├── rmdir -> coreutils
│   ├── runcon -> coreutils
│   ├── seq -> coreutils
│   ├── sha1sum -> coreutils
│   ├── sha224sum -> coreutils
│   ├── sha256sum -> coreutils
│   ├── sha384sum -> coreutils
│   ├── sha512sum -> coreutils
│   ├── shred -> coreutils
│   ├── shuf -> coreutils
│   ├── sleep -> coreutils
│   ├── sort -> coreutils
│   ├── split -> coreutils
│   ├── stat -> coreutils
│   ├── stdbuf -> coreutils
│   ├── stty -> coreutils
│   ├── sum -> coreutils
│   ├── sync -> coreutils
│   ├── tac -> coreutils
│   ├── tail -> coreutils
│   ├── tee -> coreutils
│   ├── test -> coreutils
│   ├── timeout -> coreutils
│   ├── touch -> coreutils
│   ├── tr -> coreutils
│   ├── true -> coreutils
│   ├── truncate -> coreutils
│   ├── tsort -> coreutils
│   ├── tty -> coreutils
│   ├── uname -> coreutils
│   ├── unexpand -> coreutils
│   ├── uniq -> coreutils
│   ├── unlink -> coreutils
│   ├── uptime -> coreutils
│   ├── users -> coreutils
│   ├── vdir -> coreutils
│   ├── wc -> coreutils
│   ├── who -> coreutils
│   ├── whoami -> coreutils
│   └── yes -> coreutils
└── libexec
└── coreutils
└── libstdbuf.so

3 directories, 108 files

It needs argv0 to be set to the real name of the utility. Before it was something like /tmp/tmpx-20190509T191742Z-4f90c6f0/dat/../run

[solidsnack]

Thanks for making this change. I'm not sure we can use this method -- -a ... is a Bash-ism -- but I'm sure we can do something.

It sounds like you're not calling including the binary in the tarball and calling it with a script, but rather inlining the binary, using arx -e <path/to/binary>. While we sort out setting $0, would putting the binary in the tarball work?

[matthewbauer]

Thanks for making this change. I'm not sure we can use this method -- -a ... is a Bash-ism -- but I'm sure we can do something.

Oops didn't consider that! It's definitely good to avoid that.

It sounds like you're not calling including the binary in the tarball and calling it with a script, but rather inlining the binary, using arx -e <path/to/binary>. While we sort out setting $0, would putting the binary in the tarball work?

The binary is still in the tarball. The problem is I don't want to hardcode the binary name into it. So for instance, I would like to be able to make a symlink on the outer arx script so that it propagates to the inner "$0". Here is a good way to show what happens without using -a:

$ arx tmpx // echo '$0' > exe && chmod +x exe && ./exe
/tmp/tmpx-20190510T174337Z-81443be2/dat/../run

I'd like it to show ./exe and also allow me to make a symlink so that:

$ ln -s exe exe2 && ./exe2
./exe2