x=$([ -x /etc/get_tape ] && echo /etc/get_tape; [ -x /abc/prog/bin/get_tape ] && echo /abc/prog/bin/get_tape)
This is a script.
x=$([ -x /etc/get_tape ] && echo /etc/get_tape; [ -x /abc/prog/bin/get_tape ] && echo /abc/prog/bin/get_tape)
the x is a variable
-x test if /etc/get_tape is excutable
&& (than) if /etc/get_tape is executable that is true echo the containent of /etc/get_tape.
the same applies to -x /abc/prog/bin/get_tape
please correct me if I'm wrong...
echo /etc/get_tape just echoes the same literal string /etc/get_tape back..
there are two such echoes in between the parenthesis which execute under condition and which just echo path strings...
I still didn't get how the $(...;...) construct works... and what result would be assigned to the variable x?
Will try this but would like to know what the experts here would say...
Thank you!
Vishnu.
Well semicolon lets you put two command on one line like this:
date ; uname -a
And $( ) sets x to the output of the command so x=`date` and x=$(date) do the same thing.
What the posted command is trying to do is to set x to the path of the get_tape routine. If get_tape does not exist in either place, x is null. If get_tape exists in exactly one of the places, x is that path.
But if get_tape exists in both places, x will be a two-line value with both paths in it. I wonder if the author of the code realizes that. Maybe that's what he wanted. Restricting the value of x to a single line would make this ugly construct even worse:
x=$([ -x /etc/get_tape ] && echo /etc/get_tape || { [ -x /abc/prog/bin/get_tape ] && echo /abc/prog/bin/get_tape; })
Personally, I think this really calls for explicit "if" statements. Then the code is much clearer, and much easier to maintain. But sometimes it is fun to crank out these opaque one-liners and I'm not really in a position to be casting too many stones here. 
Thank you all very much for your help.. 