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I think you are still a little caught up in the source of your data, and not considering it purely from a string processing perspective. From my reading, your goals are:

  1. Determine the number of unique 4-character prefixes (n + 1, n == 3) within a list of strings.
  2. For each prefix group, determine the longest possible string anchored at the string start common between all members of the group

If the second goal is incorrect (you've never stated it but it seems to pervade your solutions), your goal can be achieved very simply with:

#!/usr/bin/perl use strict; use warnings; my %files = (); while (<DATA>) { if (/(.{4})/) { $files{$1} = 1; } } foreach my $prefix (keys %files) { print "$prefix*\n"; } __DATA__ abcpwbln08 abcpwbln07 abcpwbnn10 abcpwbnn06 adesicln09 adesicln08 adesicln01 adesicnn05

If you want to keep the second goal, one way to accomplish your goal (TIMTOWTDI) would be to compare the new postfix with the existing solution for that prefix, and shorten that guess until it matches the to criterion:

!/usr/bin/perl use strict; use warnings; my %files = (); while (<DATA>) { if (my ($prefix,$postfix) = /(.{4})(.*)/) { if (exists $files{$prefix}) { my $pattern = $files{$prefix}; while (not $postfix =~ /^$pattern/) { $pattern =~ s/.$//; } $files{$prefix} = $pattern; } else { $files{$prefix} = $postfix; } } } foreach my $prefix (keys %files) { print "$prefix$files{$prefix}*\n"; } __DATA__ abcpwbln08 abcpwbln07 abcpwbnn10 abcpwbnn06 adesicln09 adesicln08 adesicln01 adesicnn05

In reply to Re^3: Collapsing a list of files... by kennethk
in thread Collapsing a list of files... by fiddler42

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