Question

I have a text file that looks like this.

A   102
B   456
C   678
H    A       B        C      D       E        F      G       H       I       J
    1.18    0.20    0.23    0.05    1.89    0.72    0.11    0.49    0.31    1.45
    3.23    0.06    2.67    1.96    0.76    0.97    0.84    0.77    0.39    1.08

I need to extract all the lines that start with B,H and two lines after H . How can I do this using awk?

The expected output would be

 B   456
 H    A       B        C      D       E        F      G       H       I       J
    1.18    0.20    0.23    0.05    1.89    0.72    0.11    0.49    0.31    1.45
    3.23    0.06    2.67    1.96    0.76    0.97    0.84    0.77    0.39    1.08

Any suggestions please.

Answer 1

Ignoring the blank line after B in your output (your problem specifications give no indication as to why that blank line is in the output, so I’m assuming it should not be there):

awk '/^H/{t=3} /^B/ || t-- >0' input.file

will print all lines that start with B and each line that starts with H along with the next two lines.