Shell Programming and Scripting

This is a example TXT file:
What I want to do is extract the fourth column with awk, however, there are some blank space in some field. I get wrong result when it print out awk result.

Code:

awk '{print $1,$4}' awk_column_test.txt

How will i deal with these blank spaces?

If I want print 'NULL' when the field is blank, how will I should do?

Thank you very much!

Code:

cat file

ID CDR1 CDR2 CDR3
1 CDR1   CDR3
2 CDR1 CDR2 CDR3
3     CDR3

awk '$4 == ""{$4="NULL"}{print $4}' file

CDR3
NULL
CDR3
NULL

What separator is used in your text file? Tab, space?

You might be able to tell it to use a single space or tab as the separator rather than globbing all whitespace...

Code:

awk -F"\t" '{ print $1,$4 }'
awk -F" " '{ print $1,$4 }'

Try this

Code:

~/unix.com$ awk -F\| 'gsub(/ /,"|")&&$4=$4?$4:"NULL"{print $1,$4}' f

The above script is overcomplicated, use Corona688's or in2nix4life's suggestion instead

Sorry, I can't express clearly what I mean.

The txt file could be understand like this:

ID CDR1 CDR2 CDR3
1 CDR1 NULL CDR3
2 CDR1 CDR2 CDR3
3 NULL NULL CDR3

The results I want to get should be four "CDR3". "NULL" here represents blank space, so maybe I should deal with the original file?

Thanks a lot!

---------- Post updated at 12:08 PM ---------- Previous update was at 11:50 AM ----------

Sorry, I can't express clearly what I mean. I use space as the separator.

The txt file could be understand like this:

ID CDR1 CDR2 CDR3
1 CDR1 NULL CDR3
2 CDR1 CDR2 CDR3
3 NULL NULL CDR3

The results I want to get should be four "CDR3". "NULL" here represents blank space, so maybe I should deal with the original file?

Thanks a lot!

Try -F"[ ]" if you're on Linux

From your sample code, it's impossible to find CDR3 on second and fourth line (ID 1 & 3). Is there any [tab] and [spaces] mixed?