Re: [PLUG] Variable interpolation in bash

["Michael C. Toren" <mct@toren.net>]

> This has been bugging me for a while now. When I am writting a bash 
> script, I often want to do something of the form:
> 
> 	COMMAND_OPTIONS="-foo -bar --long-opt-whos-arg 'has spaces'"
> 	command $COMMAND_OPTIONS baz
> 
> What I want to happen is for the shell to eventually execute:
> 
> 	command -foo -bar --long-opt-whos-arg 'has spaces' baz

> Running the script with bash -x shows me this:
> 
> 	+ COMMAND_OPTIONS=-foo -bar --long-opt-whos-arg 'has spaces'
> 	+ command -foo -bar --long-opt-whos-arg ''\''has' 'spaces'\''' baz

What you're really asking bash to do is expand the variable
$COMMAND_OPTIONS twice -- once to find it's contents, and once
more to perform quote expansion on those contents.  You could
try something along the lines of:

    eval command $COMMAND_OPTIONS baz

Example:

    [mct@quint ~]$ COMMAND_OPTIONS="-foo -bar --long-opt-whos-arg 'has spaces'"

    [mct@quint ~]$ (set -x; echo $COMMAND_OPTIONS baz )>/dev/null
    + echo -foo -bar --long-opt-whos-arg ''\''has' 'spaces'\''' baz

    [mct@quint ~]$ (set -x; eval echo $COMMAND_OPTIONS baz )>/dev/null
    + eval echo -foo -bar --long-opt-whos-arg ''\''has' 'spaces'\''' baz
    ++ echo -foo -bar --long-opt-whos-arg 'has spaces' baz

HTH,
-mct