Re: Practical Shebang (#!) Trick (Better Than /usr/bin/env)

On Sat, Jan 24, 2015 at 2:56 AM, William Ahern wrote:

On Fri, Jan 23, 2015 at 02:21:58PM -0800, William Ahern wrote:
> My recently released runlua utility has an option to load and skip over any
> initial shell code in the file. But I just discovered a neat trick which
> obviates the need for such a feature.
>
> #!/bin/sh
> _=[[
> exec lua "$0" "$@"
> ]]
> print("Running", _VERSION)
> print("Options", ...)
>
> Probably others have figured this out, too, but it's new to me.

Rena posted nearly the same thing a few years ago:

http://lua-users.org/lists/lua-l/2012-05/msg00171.html

His example is also portable. It doesn't rely on anything unique to bash.

Here is universal (Windows + Linux) shebang for Lua scripts.
It is compatible with all Lua versions: Lua 5.0/5.1/5.2/5.3/5.4/LiaJIT.
An executable or symlink with name "lua" must exist in the $PATH (or %PATH%) on your system.

#!/bin/sh
rem=rem--[[
: '--------------- This is batch script ---------------
@cls& setlocal& set this_file=%~0& if exist "%~0.bat" set this_file=%~0.bat
@lua "%this_file%" %*& goto :eof
'#---------------- This is shell script ---------------
exec lua "$0" "$@"
]]---------------- This is Lua script -----------------
print("Hi")
print("Press Enter to exit")
io.read()

Useful properties:
1) All arguments to batch/shell script are passed as arguments to Lua script;
2) Exit code of Lua script is propagated to exit code of this batch/shell script;
3) When invoked from command line in existing console, the control returns to the same console after Lua script terminated;
4) When invoked by double-clicking on .bat/.sh file, the console is closed on Lua script termination;
5) When run under Windows, some unwanted text is printed due to first two lines of the script, but the command "clr" clears the screen (unfortunately, all previous text written to this console is also lost);
6) When run under Linux, a garbage is assigned to env variable "rem" (do lowercase env variables never used in Linux?);

To make the same script working simultaneously in both Windows and Linux, set the file extension to ".bat" and all newlines to LF.