Storing Numerical Data in a Variable through matching in Perl - regex

Question

I am a beginner at Perl and want to store some data from a file format into a variable. Specifically, each line of the file has a format like the following:
ATOM 575 CB ASP 2 72 -2.80100 -7.45000 -2.09400 C_3 4 0 -0.28000 0 0
I was able to use matching to get the line I wanted (with the code below).
if ($line =~ /^ATOM\s+\d+\s+(CB+)\s+$residue_name+\s+\d+\s+$residue_number/)
{
}
However, I want to store the three coordinate values as variables or in a hash. Is it possible to use matching to store the coordinate values rather than having to use substring.

Answer 1

In this instance I would simply split each record into an array and verify the identifying fields. The coordinate values can simply be extracted from the array if the line has been found to be relevant.
Like this
use strict;
use warnings;
my $residue_name = 'ASP';
my $residue_number = 72;
while (<DATA>) {
my #fields = split;
next unless $fields[0] eq 'ATOM'
and $fields[2] eq 'CB'
and $fields[3] eq $residue_name
and $fields[5] == $residue_number;
my #coords = #fields[6, 7, 8];
print "#coords\n";
}
__DATA__
ATOM 575 CB ASP 2 72 -2.80100 -7.45000 -2.09400 C_3 4 0 -0.28000 0 0
output
-2.80100 -7.45000 -2.09400

Answer 2

You can get the end of the line which is AFTER the match with $' (see http://perldoc.perl.org/perlvar.html), and split around spaces like in :
if ($line =~ /^ATOM\s+\d+\s+(CB+)\s+$residue_name+\s+\d+\s+$residue_number/)
{
$_ = $';
(undef, $x, $y, $z) = split /\s+/;
...
}
(undef is necessary, because $_ will start with some spaces, thus the first variable will be empty)
You can also write something like :
if ($line =~ /^ATOM\s+\d+\s+(CB+)\s+$residue_name+\s+\d+\s+$residue_number/)
{
$_ = $';
/\s+(-?\d+\.?\d*)\s+(-?\d+\.?\d*)\s+(-?\d+\.?\d*)/;
($x, $y, $z) = ($1, $2, $3);
}
In fact, as always in Perl, there are lots of ways to do it...