Missing header in awk output

Question

input:

position fst
1 0.6
2 0.8
3 0.9
4 0.3
5 1

This gives me a header:

awk '{if ($2>=0.7) print $1}' input > output

but this doesn't:

awk '{if ($2<0.7) print $1}' input > output

How come?

Answer 1

In your second example, $2<0.7 is interpreted as "fst"<"0.7" which is FALSE

You can add NR==1 || to always print first line:

$ awk 'NR==1 || $2<0.7{print $1}' input
position
1
4

Answer 2

If you always want to print the header then use:

awk '{if (NR>1) {if ($2>=0.7) print $1} else print $1}'
awk '{if (NR>1) {if ($2<0.7) print $1} else print $1}'