why not try a regexp?

@files = qw(model4run1 model2run1 model4run2 model);

$reg = ' \\1[^ ]*' x $#files;

"@files" =~ /^([^ ]*)[^ ]*$reg$/;

print $1;
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Of course, all the usual catches apply, like having spaces, return characters, etc. in your filenames.

No idea how slow this is..

Jasper