Extracting certain rows from a text file, skipping others - perl

Question

I have a file that contains a long list of data like this:
b09 fl__2220 fuel20 ddm___an ddm___an dfl___de dfl___de dfl___de dfl___de dfl___de dfl___de dfl___de
fl dfl___de dfl___de dfl___de dfl___de dfl___de dfl___de dfl___de ddm___an ddm___an
simulated 32.9 0.0000 0.0000 0.0659 0.0888 0.1132 0.1298 0.1374 0.1413 0.1452
0.1460 0.1434 0.1404 0.1339 0.1186 0.0946 0.0708 0.0000 0.0000
measured 29.0 0.0000 0.0000 0.0579 0.0780 0.0994 0.1140 0.1207 0.1241 0.1276
0.1283 0.1260 0.1233 0.1177 0.1042 0.0831 0.0622 0.0000 0.0000
I want to extract certain data from a particular row, and then more data from a few rows ahead. From the first row I want to extract 'b09 fl__2220' and then I want to extract the fifth and sixth rows, so everything after 'measured'. The final output would look something like this:
b09 fl__2220 measured 29.0 0.0000 0.0000 0.0579 0.0780 0.0994 0.1140 0.1207 0.1241 0.1276 0.1283 0.1260 0.1233 0.1177 0.1042 0.0831 0.0622 0.0000 0.0000
I can get gawk to extract the b09 and fl__2220 with gawk '/fl__2220/ {print $1, $2}', but how do I get it to skip ahead and read the stuff from 'measured' line onwards to the last 0.0000? Or would something like perl or grep be better for situations like this?
The whole file contains similar data, eg. 'c12 fl__2211. . .', etc. But I just want the data for b09 fl__2220.

Answer 1

This is pretty simple to do in Perl. It looks like your data is fixed width so in that case you would parse it with an unpack template.
Here is the documentation.
pack tutorial
https://perldoc.perl.org/functions/unpack
https://perldoc.perl.org/functions/pack
$line =
"b09 fl__2220 fuel20 ddm___an ddm___an dfl___de dfl___de dfl___de dfl___de dfl___de dfl___de dfl___de";
#fields = unpack "A6A10";
###
### produces #fields containing ("b09", "fl__2220")
###
You would write the template for each type of line and extract it in the same manner. The A template character automatically trims trailing spaces. The number after A means how many of that type to take. A6 means take 6 characters and trim.
Another way to do it would be to use substr to pull out a number of substrings but you have to trim it yourself. unpack is usually easier.
If you are new to Perl remember to always put use strict; and use diagnostics; at the top of your script. That way you'll get a nice explanatory message whenever anything goes wrong instead of hopelessness!
HTH