pushenv() {

    # Path separator: a colon in Unix-like environments, a semi-
    # colon in Windows environments.
    SEP=":"

    maybe() {
        name=$1
        part=$(readlink -m $2)
        value=$3
        if ! [[ -d $part ]]; then
            # $part does not exist or is not a directory
            true
        elif [[ -z $value ]]; then
            echo "export $name=$part"
            export $name=$part
        elif ! [[ $value == "$part"
               || $value == "$part$SEP"*
               || $value == *"$SEP$part$SEP"*
               || $value == *"$SEP$part" ]]
        then
            echo "export $name=$part$SEP$value"
            export $name=$part$SEP$value
        fi
    }

    for dir in "$@"
    do
        maybe PATH            "$dir/bin"           "$PATH"
        maybe CPATH           "$dir/include"       "$CPATH"
        maybe LD_LIBRARY_PATH "$dir/lib"           "$LD_LIBRARY_PATH"
        maybe LIBRARY_PATH    "$dir/lib"           "$LIBRARY_PATH"
        maybe PKG_CONFIG_PATH "$dir/lib/pkgconfig" "$PKG_CONFIG_PATH"
    done
}