Sorry to correct you, but this is NOT a typo and it was indeed intended that way. Here is a bit of UNIX history:

The UNIX kernel has to have some clue about what constitutes an executable file. OK, there is the x-bit in the filemode, but still, the kernel has to know what to do. For binary files there is the so-called "magic number", which is the first 4 bytes of an executable. Look at any first 4 bytes of binary, compiled files in your system and you will see that they are the same.These 4 bytes tell the kernel to use some member of the exec*() family of system calls to actually execute it.

Unfortunately this is not possible with the input files of the many interpreters a system has: all sorts of shells, awk, sed, many editors (ed, ex, ...) which can be scripted, and so on. Historically there was only one shell and the UNIX kernel had a special provision to try invoking the shell with the file as input in case the magic number was not understandable. Today this has been altered to the system default shell and is still in place: you can see it at work when you write a script without any shebang line. In this case the startup process is like: the kernel finds no valid magic number, then loads the system default shell (which is a normal executable binary) via normal exec*(), then feeds it the file in the hope that the shell can make sense of it. If it is indeed a shell script, it does. If not, you will see some error message, which is coming from the shell, not the kernel itself.

But as UNIX evolved and many different shells (and other interpreters of script-like text) were available the developers of UNIX searched for ways to name the specific shell/interpreter for scripts. The UNIX kernel was extended for a new magic number and this four-byte code was:

Code:

#! /

If the kernel finds this magic number it reads the rest of the first line, loads the specified interpreter and - upon succeeding in that - feeds it the file as input. Because the '#' is a comment to the shell it doesn't alter any script at all, the shell will just ignore it like any other comment.

This is the reason why you have to have the shebang in the very first line and why it is not allowed to be indented and why you have to use the absolute path of the shells executable: #! /bin/bash is a legal shebang, #! ../../bin/bash is not.

So, basically, the correct shebang line is:

Code:

#! /path/to/interpreter

Unfortunately most people were not able to reliably put a single space where it belongs and many wrote

Code:

#!/path/to/interpreter

Which was still a normal comment and the kernel would - failing to recognize the magic number - still load the default shell, but maybe not the specified one. Which is why the kernel was extended again to also recognize a special 3-byte magic number, which was the shebang without the space.

This is the situation we have now. Basically it doesn't matter any more if you write the space or not, but, being as old as i am, you have to have something that sets you apart from the youngsters (save for having to get up at three in the morning to pee). Therefore i always write the "originally correct" shebang, and not these newly-invented hacks which are only going back to the seventies.

I hope this helps.

bakunin