Similar to "apropos"

[jb_fvwm2]

pkgconf --list-all | grep audio | lookat

The third item in the pipe, here rendered the output more easily readable (less line wrapping...)
That parameter was in a post to the freebsd-ports list today. Never thought to use pkgconf as an inquiry to installed packages...

 

[phoenix]

Note: not every application uses pkgconf, so this will only list information about pkgconf-using apps (mainly GNOME/GTK stuff).

 

[kpa]

Also note that the pkgconf stuff is for detecting dependencies at compile time without using any knowledge of installed packages, the ports system requires that the ports must compile and install completely even if the package registration is disabled.