Is space allowed between #! and /bin/bash in shebang?

Question

In a shebang, is a space or more allowed between #! and the interpreter?

For example, #! /bin/bash. It seems work, but some said that it is incorrect.

Answer 1

Yes, this is allowed.

The Wikipedia article about the shebang includes a 1980 email from Dennis Ritchie, when he was introducing kernel support for the shebang (as part of a wider package called interpreter directives) into Version 8 Unix (emphasis mine):

The system has been changed so that if a file being executed begins with the magic characters #!, the rest of the line is understood to be the name of an interpreter for the executed file. […]

To take advantage of this wonderful opportunity, put

#! /bin/sh

at the left margin of the first line of your shell scripts. Blanks after ! are OK.

So spaces after the shebang have been around for quite a while, and indeed, Dennis Ritchie’s example is using them.

Note that early versions of Unix had a limit of 16 characters in this interpreter line, so you couldn’t have an arbitrary amount of whitespace there. This restriction no longer applies in modern kernels.

Answer 2

Yes, blanks are allowed after the #!. There was even a (mistaken) thought that some systems might require it, but it has always just been optional.

For further reading try here

Answer 3

FYI, some versions of systemd fail to parse shebangs with a space. With a service like this:

[Service]
Type=oneshot
ExecStart=/root/foo.sh

... and a shebang like this:

#! /bin/bash

... you may get an error like this:

systemd[32834]: foo.service: Failed at step EXEC spawning /root/foo.sh: Exec format error

Removing the space from the shebang fixes the error. So look out for that one.