How to import specific lines from dat file - file-io

Question

I've got a .dat file with numbers that I need imported into a SAS dataset. However, there's plenty of information that I do not need, and I only want specific lines of data (e.g. every 6th line starting from line 1000, until I have 100 observations). I also require a unique identifier based on what is displayed on the first line.
So for example, the .dat file contains this:
DATANOTREQUIRED
DATANOTREQUIRED
DATANOTREQUIRED
UPDATE AAA_1111111_Q_BBBBBB_0_1_#
123.4,
123.5,
124.0,
124.1
DATANOTREQUIRED
DATANOTREQUIRED
DATANOTREQUIRED
UPDATE AAA_1111111__Q_BBBBBB_0_2_#
125.1,
126.0,
127.1,
130.0
What I want the eventual SAS dataset to look like is this
Identifier | Value
X.1. | 124.1
X.2. | 130.0
I'm using the infile in SAS and using input to point to line 1000 but I'm stuck and cannot get the SAS dataset I want. (Updated code based on contributors below)
data work.test;
infile '\\filepath\mydatasource.dat' dsd firstobs=1042 truncover;
input #8 ID :$40.
#4 Value1 :8.;
run;
but what I'm seeing now is that the header lines are appearing fine, but the first observation has a . and instead the first data value is appearing for the 2nd header line.
ID | Value1
UPDATE AAA_1111111_Q_BBBBBB_0_1_# | .
UPDATE AAA_1111111__Q_BBBBBB_0_2_# | 124.1

Answer 1

Here's an example assuming that you have the same number of rows between each header row:
data want;
if _n_ > 2 then stop; /*Stop after we've output 2 rows */
infile cards firstobs=6; /*Skip the first 5 lines in the file*/
input #1 #8 ID :$32.
#5 myvar :8.;
cards;
UPDATE AAA_1111111_Q_BBBBBB_0_1_#
123.4,
123.5,
124.0,
124.1
UPDATE AAA_1111111__Q_BBBBBB_0_2_#
125.1,
126.0,
127.1,
130.0
UPDATE AAA_1111111_Q_BBBBBB_0_3_#
123.4,
123.5,
124.0,
124.1
UPDATE AAA_1111111__Q_BBBBBB_0_4_#
125.1,
126.0,
127.1,
130.0
;
run;

Answer 2

Use the FIRSTOBS= option to skip the beginning of the file.
If there are always 5 records per block you could just read them individually.
data want;
infile rawdata dsd firstobs=1000 truncover;
input id :$40. (4*value) (/) ;
run;
Or you could do something like this that should allow for a variable number of values per id and just keep the last one.
data want;
infile rawdata dsd firstobs=1000 end=eof;
input # ;
length id $32 value 8 ;
retain id value;
if _infile_ =: 'UPDATE' then do;
if _n_ > 1 then output;
id = scan(_infile_,-1,' ');
end;
else input value;
if eof and _n_ > 1 then output;
run;