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Details about the shebang/hash-bang mechanism on various Unix flavours (2001)

87 points by js2

by rmunn

1 subcomments

Not mentioned there, because it's discussing history that nearly all happened before Unicode was ever conceived, is the fact that the kernel expects the first two bytes to be #! and therefore a UTF-8 BOM will mess up this logic. If the first two bytes are 0xEF 0xBB (because the first five bytes where 0xEF 0xBB 0xBF hash bang), you'll get errors like "./doit.sh: line 1: #!/bin/bash: No such file or directory" and be left scratching your head. /bin/bash is right there, I can see it with ls, why can't my script see it?
Do you see the invisible BOMb in the error message? Neither did I the first time. (And, in fact, Ghostty apparently stripped it out when I copied and pasted, so it's not actually there in this comment). But if I were to load that doit.sh script I created for this example into VS Code, I'd see the telltale "UTF-8 with BOM" file format.
Most people already know this, but maybe this will help someone out there. If you see a "No such file or directory" error and the program being executed apparently starts with #!, it probably actually starts with U+FFEF#! and you need to re-save the script in UTF-8 without a BOM(b) at the start.

by Ferret7446

0 subcomment

The article actually mentions this in passing, but POSIX will default to running the file with the system shell if it's not an executable binary. So hashbang scripts can work even if the system doesn't support hashbangs (as long as the script is in shell).
See also https://www.felesatra.moe/blog/2021/07/03/portable-bash-sheb...

by rmunn

1 subcomments

Also relevant: https://news.ycombinator.com/item?id=45970885 (article about how #! allows relative paths)

by AnssiH

1 subcomments

by xrd

0 subcomment

I got really excited about a #!magic invocation only to be disappointed. But this is still a fun romp.

by John-Tony12

0 subcomment