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awk question - getting ip from ifconfig

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# 1  
Old 12-11-2009
awk question - getting ip from ifconfig
Hi there, I have a script which loops through the physical interfaces of a box and populates a variable called $NIC with the interface name

so if for example $NIC is equal to "e1000g0", I am trying to figure out some awk that will get the IP for that interface from ifconfig output

Code:
lo0: flags=2001000849<UP,LOOPBACK,RUNNING,MULTICAST,IPv4,VIRTUAL> mtu 8232 index 1
        inet 127.0.0.1 netmask ff000000 
e1000g0: flags=201000843<UP,BROADCAST,RUNNING,MULTICAST,IPv4,CoS> mtu 1500 index 2
        inet 10.1.1.1 netmask ffff0000 broadcast 10.1.255.255
        ether 0:14:4f:xx.xx.xa
e1000g1: flags=201000843<UP,BROADCAST,RUNNING,MULTICAST,IPv4,CoS> mtu 1500 index 2
        inet 10.1.1.2 netmask ffff0000 broadcast 10.1.255.255
        ether 0:14:4f:xx.xx.xb

Ive been trying to set up an awk statement that sets a variable called X to "1" when it find the interface in question (in this case e1000g0) and then start searching for the line containing the string "inet", then print £2 and set X=0 again so that it wont print any more

Apologies for my inexperience with awk, but does am i close with the following syntax ? please feel free to shoot me down :-) ive been trying all sorts of variatiosn but i cant get it to work

Code:
#echo $NIC
e1000g0
# ifconfig -a|nawk 'BEGIN { NIC=$NIC ; X=0} ; /NIC/ {X=1} ; /inet/&&X{print $2 ; X=0}'

Any help on this would be really apreciated
# 2  
Old 12-11-2009
Code:
NIC=$NIC

shell replacement will not be handled by awk

you should probably do something like..

Code:
awk -v nic=$NIC '{ awk statments.....}'

# 3  
Old 12-11-2009
It seems to work when i do this

Code:
# ifconfig -a | nawk  'BEGIN {x=0};/e1000g0/{x=1};/inet/&&x{print $2}'
10.1.1.1

i.e if i define the nic name specifically in the command
# 4  
Old 12-11-2009
correct.
because in your previous statement NIC contains actually nothing. ( it is not replaced by e1000g0 what you were expecting )

if you really dont want to hardcode the value then use -v command line option as i suggested earlier.

instead
Code:
# ifconfig -a | nawk  'BEGIN {x=0};/e1000g0/{x=1};/inet/&&x{print $2}'

this should work

Code:
# ifconfig -a | nawk  -v nic="$NIC" 'BEGIN {x=0};/nic/{x=1};/inet/&&x{print $2}'

# 5  
Old 12-11-2009
Or:

Code:
ifconfig -a | awk -v var="e1000g0" '$0 ~ var{getline;print $2;exit}'

# 6  
Old 12-11-2009
Quote:
Originally Posted by anchal_khare
correct.
because in your previous statement NIC contains actually nothing. ( it is not replaced by e1000g0 what you were expecting )

if you really dont want to hardcode the value then use -v command line option as i suggested earlier.

instead
Code:
# ifconfig -a | nawk  'BEGIN {x=0};/e1000g0/{x=1};/inet/&&x{print $2}'

this should work

Code:
# ifconfig -a | nawk  -v nic="$NIC" 'BEGIN {x=0};/nic/{x=1};/inet/&&x{print $2}'



Thanks for your help on this, I have tried

Code:
#echo $NIC
e1000g0
# ifconfig -a | nawk  -v nic="$NIC" 'BEGIN {x=0};/nic/{x=1};/inet/&&x{print $2}'
#

unfortunately returns no output

again returns to the next line with no output .... i think i am missing something here

---------- Post updated at 09:39 AM ---------- Previous update was at 08:44 AM ----------
Quote:
Originally Posted by Franklin52
Or:

Code:
ifconfig -a | awk -v var="e1000g0" '$0 ~ var{getline;print $2;exit}'


Franklin, if i replace the awk with a nawk this works perfectly (thankyou). if i use awk, i get syntax errors

although i dont quite understand how your statement works as im more used to the learning the if/then awk constructs, i will use it because i cant get the ones that seem logical to me to work Smilie

thankyou very much all
Last edited by rethink; 12-11-2009 at 10:37 AM..
# 7  
Old 12-11-2009
Quote:
Originally Posted by rethink

although i dont quite understand how your statement works as im more used to the learning the if/then awk constructs, i will use it because i cant get the ones that seem logical to me to work Smilie

thankyou very much all
Explanation:

Code:
$0 ~ var		# if the pattern matches the line
{getline;print $2;exit}	# then read the next line, print the second field and exit

In contrast with the next statement getline reads the next line and continues with the next statement
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