This matching pattern with the use of lookarounds delimited by spaces extracts the filename you require. When you say delimiters I am hoping you are referring not to the spaces between each character blocks.
#!/usr/bin/perl
use warnings;
use strict;
my $line = q{3,"2014-02-19 14:29:05","Extracted 1 Unfulfilled Reconcil
+iation records into /opt/mysql/backup/recon/201312/input/UNFULFILLED_
+RECONCILIATION_20130225.CSV","URECONCILIATION"};
$line =~ m{
\s\S*?(?!\.CSV) # space delimited text filter
\s(\S*?(?<=\.CSV)) # filename
}x;
print $1;
Edit: ah, one liner as in need to pipe it or so. oops sorry thought you were after the pattern.
