Thanks to Markus Wiesner.

Signed-off-by: Robby Workman <rworkman@slackware.com>

Signed-off-by: Robby Workman <rworkman@slackware.com>

Signed-off-by: Robby Workman <rworkman@slackware.com>

There is a slight problem with things like
  grep lo: /proc/net/dev
especially with tun/tap devices with can have arbitrary names.

Consider a scenario where you name your tap iface "trololo":
$ grep -c lo: /proc/net/dev
2
$

To fix this (quite hypothetical, but still) problem, instead
of simple grepping in /proc/net/dev, check of sysfs path
existence (/sys/class/net/<interface>).

Same fix in if_up() and if_down() for non-loopback interfaces.

While there, also strip colon-whatever from interface name
(what I think was the original idea behind a construct like
grep $(echo ${1}: | cut -f 1 -d :): /proc/net/dev) by using
parameter expansion: ${1%%:*} will remove the longest suffix
matching ":*", ie. colon-and-everything-after.
This is supported by POSIX:
http://pubs.opengroup.org/onlinepubs/009695399/utilities/xcu_chap02.html

Alternative solution would be to change the grep pattern to
  grep '^ *lo:' /proc/net/dev

Signed-off-by: Robby Workman <rworkman@slackware.com>

The only places using "num" already clear it with "num=0"

Signed-off-by: Robby Workman <rworkman@slackware.com>

Add same comment as in 4561bd10747935edf3e4f17ad18768d17ee95a4e

Signed-off-by: Robby Workman <rworkman@slackware.com>

Signed-off-by: Robby Workman <rworkman@slackware.com>

This is the correct usage to produce one string from all
elements of an array.

foo[0]=b
foo[1]=a
foo[2]=r

"${foo[@]}" here would mean "b" "a" "r"
"${foo[*]}" however: "b a r", and that's what we mean when
logging it.

Signed-off-by: Robby Workman <rworkman@slackware.com>