remove blank lines in awk display

Question

I was trying to figure out a solution for this question. I wanted to use awk for the solution.

My input file is something like below.

-bash-3.2$ cat file
ramesh
ramesh_venkat
ramesh3_venkat3
ramesh4
ramesh5
venkat
venkat3
venkat4

I used awk command to extract the second values after _ as below.

awk -F "_" '{print $2}' file

However, though the above command prints the correct values I am getting blank lines in my output. I have 2 questions.

Question 1

How can I remove the blank lines in output so that I get only venkat and venkat3 in the output?

If I use printf instead of print in my awk, I get venkatvenkat3 as output which is not I wanted to achieve. I want the output like,

venkat
venkat3

Question 2

Using those values as an associative array or something, how can I find if the values actually occur in $1 column?

I wanted to achieve something like,

awk -F "_" '$2==1{print $1}' file

EDIT

I did not notice the awk solution of Stephane. Is it doing the same thing that I had mentioned?

Stephane's `awk` is not doing the same thing. Your approach assumes that a word can only be contained in another if it is separated by `_`. While that is true for the OP's example, all of the posted answers also deal with cases like `doglion` and not only `dog_lion`. — terdon, May 07 '14 at 16:52
For non-awk, see: [How to remove blank lines from a file in shell?](http://unix.stackexchange.com/q/101440/21471) — kenorb, May 05 '15 at 16:05

score 12 · Answer 1 · answered May 07 '14 at 16:55

12

Another approach:

awk -F_ '$2{print $2}' file

This will only print if $2 is defined. It is a shorter way of writing:

awk -F_ '{if($2){print $2}}' file

Don't have anything to add that has not already been addressed.

answered May 07 '14 at 16:55

terdon

cuonglm · Accepted Answer · 2015-12-29T17:07:22.007

10

Question1

$ awk -F _ 'NF > 1 {print $2}' file
venkat
venkat3

Question2

$ awk -F _ '
    NR == FNR {a[$1];next}
    ($2 in a) {print $2}
' file file
venkat
venkat3

edited Dec 29 '15 at 17:07

answered May 07 '14 at 15:32

cuonglm

I need to display `venkat` and `venkat3` as per the OP asked in the other question. I am trying to find if the key after `_` is present in my `$1` column. – Ramesh May 07 '14 at 15:43
Oh, I have updated my answer! – cuonglm May 07 '14 at 15:46
Nice solution. I think you should add this one also to your solution in the other question :) – Ramesh May 07 '14 at 15:48

score 8 · Answer 3 · answered May 07 '14 at 15:33

8

for Question 1, you could use the --only-delimited (-s) option of cut

cut -s -f2 -d'_' file
venkat
venkat3

answered May 07 '14 at 15:33

iruvar

score 6 · Answer 4 · answered May 07 '14 at 15:29

6

question 1

awk -F "_" '/_/ {print $2}' file

question 2

awk -F "_" '{values[$1]=1;}; END {for (val in values) print val;}' file

answered May 07 '14 at 15:29

Hauke Laging

For question2, I intend to get only `venkat` and `venkat3` as output as they are present in `$1`. However, I get all the `$1` values as per your command. – Ramesh May 07 '14 at 15:37
@Ramesh: As your describtion, I think you want to get `$2` of entry that have `$2` occurs in 1st column. Is this right? – cuonglm May 07 '14 at 15:43
@Gnouc, yes you are right. – Ramesh May 07 '14 at 15:44

4 Answers4