Extract Lines when Column K is empty with AWK/Perl

Question

I have data that looks like this:

foo 78 xxx
bar    yyy
qux 99 zzz
xuq    xyz

They are tab delimited. How can I extract lines where column 2 is empty, yielding

bar    yyy
xuq    xyz

I tried this but doesn't seem to work:

awk '$2==""' myfile.txt 

Answer 1

You need to specifically set the field separator to a TAB character:

> cat qq.in
  foo     78      xxx
  bar             yyy
  qux     99      zzz
  xuq             xyz
> cat qq.in | awk 'BEGIN {FS="\t"} $2=="" {print}'
  bar             yyy
  xuq             xyz

The default behaviour for awk is to treat an FS of SPACE (the default) as a special case. From the man page:

In the special case that FS is a single space, fields are separated by runs of spaces and/or tabs and/or newlines. (my italics)