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.


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.


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

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