Re: [PATCH 1/4] t0021: use write_script to create rot13 shell script

> On 06 Nov 2016, at 15:29, Jeff King <peff@peff.net> wrote:
> 
> On Sun, Nov 06, 2016 at 03:25:33PM +0100, Lars Schneider wrote:
> 
>> This looks good to me (and it works on my machine).
>> However, I took a look at the "write_script" function and found this,
>> added by Junio in 840c519d:
>> 
>> echo "#!${2-"$SHELL_PATH"}" &&
>> 
>> There is some kind of variable expansion happening with the "2-" but
>> I can't quite figure out what is going on. Plus, I can't find anything 
>> about this in the sh docs.
>> 
>> Can anyone help me to understand it?
> 
> See the section on parameter expansion in "man bash". Basically:
> 
> ${foo:-bar}
> 
> expands to $foo, or "bar" if it is unset or empty. Without the colon:
> 
>  ${foo-bar}
> 
> expands to $foo, "bar" if it unset (but not if it is empty).