From the Jargon Dictionary: http://info.astrian.net/jargon/terms/s/shebang.html
shebang /sh*-bang/ n. 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).
This is the resurrection of an old project (circa 2002).
Shebang extends the standard shebang line functionality found on Linux, Mac OSX and Windows Cygwin allowing for use cases that would be otherwise impossible.
Let's start with a brief introduction about what the standard shebang really is.
In Unix-like operating systems, when a script containing the two specific characters #! as the first 2 of the file being executed, then the rest of the line is intrpreted as the interpreter directive and the original script file path is passed to this interpreter as a command line argument. For this to happen, the original script requires the execute attribute be set.
One of the most common uses is to run shell scripts.
#! /bin/bash
echo "Hello World!"This may allow you to execute the scripts with a different shell than your login shell.
You may wonder why somebody would like to do something like this. After all, is there any other shell than bash?
Certainly, there are, even though bash is almost everywhere. If you are interested in some historical facts related with Unix shells taka a look at superuser: why is bash everywhere....
To cut this story short, in ancient times, you may have had csh as your login shell because of features like history
and job control but you still wrote your scripts in sh. In such cases, the shebang line came very handy.
There are other cases indeed, not related to login shell, for example to execute scripts that are programmed in a different language than the shell
#!/usr/bin/awk -f
/localhost/ {print $1}or
#! /usr/bin/env python
print "Hello World!"As we mentioned before, once the interpreter directive is honored then the interpreter is invoked with the original script file path as an argument.
But, what if the interpreter does not support # as a comment?
Well, if the interpreter does not support it as a comments you will receive a syntax error.
Another limitation is that the shebang line is passed verbatim to the interpreter, no variable expansion of any kind is performed. In this respect shebang, this ustility, helps by providing some basic variable expansion feature.
Regarding arguments provided in interpreter command lines is not well defined how they would be treated. Different Unix-like systems treat them in different ways and sometimes the interpreter is invoked with a single argument concatenating all the arguments provided in the original shebang command line (see Results).
This shebang utility also tries to unify shebang and command line arguments treatment across different platforms.
permits that programs that accept scripts but don't allow '#' as a comment, be used with shebang (#!) interpreter method of execution. This is because the entire script is passed to the interpreter untouched, including the first (shebang) line. If '#' is not understood as a comment, probably you get a 'syntax error' from the interpreter.
Now you can write scripts that will be executed by those programs with no conflict.