perlquestion Anonymous Monk Hello<p> I cannot get the following code to capture what is in a lookahead (when the lookahead is within capturing parens. .<p> What I'm trying to achieve is to capture substrings of length 'x' beginning with the first character in the fasta sequence (and the lookahead portion) progressing from the first character, the second, and so on, until the substrings run up against the end of the characters. <p>Thanks in advance for any help.<p>Chris <code> #!/usr/bin/perl use strict; use warnings; my $str = do {local $/; <DATA>}; $str =~ s/\s+//g; my $len = length $str; while (--$len > 780) { while ($str =~ /(.(?=.{$len}))/g) { print pos, "$1\n"; } pos = 0; } __DATA__ CAATATGCGAGGGACCTACATGTTGAGCATGACAATGAATTCTATTGAAAAAAAGAGTTG GAAGTATATACGAATATAAATAATGTGAAACAAAAGAAGAAAAGTGAATAAAAGGCACTT AAGACGCTATCCAATTGTGTATGAGAAGTGCAAACTCAATTTTTTTGCAAAAGACTTTTC TCAAACCTTTAATTGATGCGTTCCGTTCATACATCAACCGCGTCCCATACGTTTCGAAGA AAATTGCCTATATGTGTTATTTACATACTAGAGATATTTTAATATTGAAACAGTTGTATT TCTATTGTAATTACTATCTAAACGTCTCGTCCCACCGCTGTTGATAAAGCGGTGCCAATA TAATTTATAATCACGCCTGGGTAAATGACTTTTAATTTCTTAAATCATCGAAGTATGCGA AAACAAGAAGTCTTTATTCATAATAAAAAACAAATTCGGTTACTACGACTTTTATATGTC ATTCAATATTTGGTAATAATTTTACAGTATTAACCCTATCCTCATCTGATTCACTCTCTT CTAATTGCATATATTTTCAAATTCGCTTTCAGCGCTGTACAAAACCAGTAAGCAGATCTC GTACGAAGACTCAAATAAGTTGCATTGTTCGTATTCAAGGAAACCGGGGGGCAAAATTTC CAACCATATTTAAGTATGACAATATTTCCAAGTCAAGGATGCATGCTGTTCTTCTCTTCA TTAACTAGCTAACCAATTAGCTGAACGGCTTTGTATTTTACTTAACATATTGTCTATTGC ATAAAAAACCACTATTCAGC </code> 7