Next try... 

/^(([a-zA-Z0-9]{2,}_)*[a-zA-Z0-9]{2,})$/ && print "$_\n" 
    for "1", "a\n", "aa\n", "a_", "aa", "aa_bb_cc_dd", "a1_11_1c_11", 
+"aaa", "aa_";

[download]

Still matches a trailing newline. It does not match "aa_" on purpose as this is not a sequence of two or more alphanumeric characters separated by underscores which was my claim if not the original question.

In reply to Re^3: Looking for a regular expression for the following pattern. by hdb
in thread Looking for a regular expression for the following pattern. by skooma

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