Shebang
The first line of shell scripts is most commonly written without a space, ie #!/usr/bash however in the examples of O’Reilly’s sed & awk book it’s written #! /bin/sh
According to this stackoverflow post
The shebang (#!) is a 16-bit kernel-interpreted magic “number” (actually 0x23 0x21). Thereafter, the kernel program loader (following the exec-family call) attempts to execute the remainder of the line to handle the remainder of the containing file’s content. Many, if not most modern kernels disregard preceding spaces to the command that follows the shebang. As such, #! /bin/bash, #! /usr/bin/perl, and the like, should be acceptable with most modern kernels. That said, a shebang with no following space is far more commonly seen.
The sed & awk books includes this note:
You can put only one parameter on the “#!” line. This line is processed directly by the UNIX kernel; it is not processed by the shell and thus cannot contain arbitrary shell constructs