Question

Following command doesn’t pick 2nd string from odd line and 4th from odd-even line.
show_statistic.sh | grep -A 1 vlan | awk '{ if ( ( NR % 2 ) == 1 ) { print $2 } else { print $4 } }'
It prints each line’s second and fourth string. What I did wrong?

Answer 1

It looks like your expected result is from the lines containing “vlan” and the following ones.

Your code will work with an unique response, but with more response than one your differents results will be separated bi a line containig only “–” as documented in grep :

  -A NUM
      Places  a  line  containing  a  group  separator  (--)   between
      contiguous  groups  of  matches.  With the -o or --only-matching
      option, this has no effect and a warning is given.

So with this line more you will want the second argument on line 1, 4, 7…
And the fourth on line 2, 5, 8…

So you code can be :

show_statistic.sh | grep -A 1 vlan | awk '{  if ( ( NR % 3 ) == 1 ) { print $2 } else { if ( NR % 3 == 2 ) { print $4 } } }'

I write a little text file to test :

1line here
2foo
vlan 2a 3a 4a 5a
1 2 3 4 5
bar

line here
vlan 2a 3a 4a 5a
1 2 3 4 5
line here
baz

The result is :

$ grep -A 1 vlan file| awk '{  if ( ( NR % 3 ) == 1 ) { print $2 } else { if ( NR % 3 == 2 ) { print $4 } } }'
2a
4
2a
4