Thanks perderabo,
of course I already tried this but here is my concern :
in fact i'm using the following command :
egrep_source argument="-ni $1" where egrep_source is an embedded egrep working in a configuration management tool...
And, as you can see, the quotes are already present and mandatory for egrep_source to work.
The only way I found to solve this is entering the command :
loc arg1 "arg2 arg3 arg4"
with the following code :
egrep_source argument="-ni $1" | egrep $2
This works of course, but I don't really like it !
If you have a better idea...