FreeBSD Ports: How to see all dependencies for a port, and all subdependencies for those dependencies

Here's a lightly-tested solution:

#!/bin/sh

# Build a regex to match all the .pm files
_regex=""
for arg in $*; do
    arg=`echo ${arg} | sed -e 's|::|/|g'`
    if [ "X${regex}X" != "XX" ]; then
        regex="${regex}|"
    fi
    regex="${regex}(${arg})"
done
regex="%%SITE_PERL%%/(${regex}).pm"

# Find the .pm files and derive the port names from them, then install using portinstall.
find /usr/ports -type f -name pkg-plist -path '*/p5-*' -exec egrep -l $regex {} + | sort -u | sed -e 's|/usr/ports/||' -e 's|/pkg-plist||' | xargs portinstall

Now, this won't detect modules installed by ports which don't have a pkg-plist but they're very much in the minority. There's only 58 out of 4188 p5-* ports on my system which don't have pkg-plist files.

My suggestion would be pkg_cutleaves (available in the ports collection), or pkg-orphan -- Both of these do the same basic thing (list packages that aren't referred to as a dependency by any other package, and ask you what to do).

I wouldn't bother though: The build dependencies will just have to be rebuilt and reinstalled when you upgrade the port, and they generally don't take up huge amounts of room. Leaving them won't hurt you unless your system is severely disk-space constrained.