Very Computer

Hi,

(GNU bash, version 2.05b.0(1)-release (i586-mandrake-linux-gnu).)

Is it possible, in the above version of BASH, to have (a) command
substitution(s) within (a) parameter substitution(s)?  I tried the
following in a BASH script:

gqview ${$( cat $HOME/mydisplay_return )#*\ }

and it didn't work.  The above code line was to execute GQview (an image
viewer) with the name of an image file that was stored, on it's own, in a
file called 'mydisplay_return', hence the 'cat' command to get at the image
file name.  The file name stored in the 'mydisplay_return' file was
prefixed with an identifying number followed by a space, hence the '#*\ '
parameter substitution to just leave the file name.  But it doesn't work.
What's wrong?

Yours,
Gary Hayward.

No.

Quote:> gqview ${$( cat $HOME/mydisplay_return )#*\ }

> and it didn't work.  The above code line was to execute GQview (an image
> viewer) with the name of an image file that was stored, on it's own, in a
> file called 'mydisplay_return', hence the 'cat' command to get at the image
> file name.  The file name stored in the 'mydisplay_return' file was
> prefixed with an identifying number followed by a space, hence the '#*\ '
> parameter substitution to just leave the file name.  But it doesn't work.
> What's wrong?

If this was going to do anything, I would expect it to run the 'cat'
first, then use the output of that as the variable name, and then edit the
value of that variable. However it doesn't even do that.

Do what you want in 2 steps.

x=$(car $HOME/mydisplay_return)
gqview "${x#*\ }"

or, since you already are running an external program

gqview $( sed 's/.* //'  $HOME/mydisplay_return)

(Of course there is

read x < $HOME/mydisplay_return
gqview "${x#*\ }"

as well)

   You are trying to use parameter expansion on something that is not
   the name of a variable. (If the result of $(cat ...) were the name
   of a variable, you could do it with eval; but it's not.)

   When a complex command is causing problems, break it up:

read var < "$HOME/mydisplay_return"    ## no need for cat
gqview "${var#* }"

--
    Chris F.A. Johnson                     <http://cfaj.freeshell.org>
    ==================================================================
    Shell Scripting Recipes: A Problem-Solution Approach, 2005, Apress
    <http://www.torfree.net/~chris/books/cfaj/ssr.html>