The Collaborative International Dictionary of English v.0.48:

Shebang \She*bang"\, n. [Cf. Shebeen.]
   1. A jocosely depreciative name for a dwelling or shop; a
      primitive dwelling; a shanty. [Slang, U.S.]
      [1913 Webster]

   2. The structure of an object, process, organization, or
      anything viewed as complicated; -- used primarily in the
      phrase

   the whole shebang; as, it comes with unnecessary frills,
      but you have to buy the whole shebang. [informal]
      [PJC]

   3. (computers) [Possibly derived from shell bang; the
      character ! is referred to in some computer contexts as
      bang.] The character sequence #!, which frequently begins
      shell scripts in a Unix system.
      [PJC]

WordNet (r) 3.0 (2006):

shebang
    n 1: an entire system; used in the phrase `the whole shebang'

The Jargon File (version 4.4.7, 29 Dec 2003):

shebang
 /sh@?bang/, n.

    [possibly a portmanteau of ?sharp bang?] The character sequence ?#!? that
    frequently begins executable shell scripts under Unix. Probably derived
    from ?shell bang? under the influence of American slang ?the whole shebang?
    (everything, the works).


The Free On-line Dictionary of Computing (30 December 2018):

shebang

    (Or "shebang line", "bang path")
   /sh*-bang'/ (From "sharp" and "bang") The magic cookie
   "#!" used in Unix to mark the start of a script, e.g. a
   shell script or Perl script.

   Under Unix, if the first two bytes of an executable file
   are "#!", the kernel treats the file as a script rather than
   a machine code program.  The word following the "!" (i.e.,
   everything up to the first whitespace) is used as the
   pathname of the interpreter.  For example, if the first
   line of an executable is

    #!/usr/local/bin/perl

   the script will be treated as a Perl script and passed as an
   argument to /usr/local/bin/perl to be interpreted.  Some
   variants of Unix also allow one or more parameters to be
   passed to the interpreter, for example, you can write

    #!/usr/bin/perl -w

   and the script will be started as if you typed

    /usr/bin/perl -w 

   on the command line.  Also, most modern kernels ignore any
   whitespace between the "!" and the interpreter pathname.  Even
   some modern kernels have fairly small limits (e.g. 32) on the
   length of line they will accept, making long pathnames and
   arguments somewhat unportable.

   [Does anyone call this a "magic string"?]

   (1998-05-06)