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Simple Shell Programming Question: [ $( )]

I've been poking around Arch Linux's network scripts, and I can't seem to figure these lines out:

Code:

[ "$(/sbin/ifconfig ${1} 2>/dev/null | /bin/grep -v 'inet6 addr: fe80:' | /bin/grep -e 'inet addr:' -e 'inet6 addr')" ] && return 0

(these lines are to find out if an interface is up. The return exits the function that would bring the interface up if the interface were running)

I know what everything does execpt $(/sbin/ifconfig ${1} 2>/dev/null)

why is this in $() and that inside []?

these parentheses with a dollar sign in front is confusing me.

$(command) is same as the backtick symbol used in earlier versions .

for e.g
instead of

for file in `ls`

I can do
for file in $(ls)

Thanks. Thats all I need to know.