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^(?i:)(?!.*MEDICAID).*ATB.<wbr />*XLS$
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That was exactly what I needed. Thanks for the quick response, I really appreciate it!
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That was exactly what I needed. Thanks for the quick response, I really appreciate it!

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Thanks for the question and the points.
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I need to use Regular Expressions to identify file names by this criteria:<br />
&nbsp; 1 contains the word ATB<br />
&nbsp; 2 does not contain the word MEDICAID<br />
&nbsp; 3 ends with XLS<br />
&nbsp; 4 search pattern is case insensitive.
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I need to use Regular Expressions to identify file names by this criteria:
  1 contains the word ATB
  2 does not contain the word MEDICAID
  3 ends with XLS
  4 search pattern is case insensitive.

How to use Regular Expression to identify a string containing the word ATB and does not contain the word MEDICAID and ends with XLS

A regular expression ("regex") is a sequence of characters that define a search pattern, mainly for use in pattern matching with strings, or string matching, i.e. "find and replace"-like operations. Regular expression processors are found in several search engines, search and replace dialogs of several word processors and text editors, and in the command lines of text processing utilities, such as sed and AWK. Many programming languages provide regular expression capabilities, some built-in, for example Perl, JavaScript, Ruby, AWK, and Tcl, and others via a standard library, for example .NET languages, Java, Python and C++ (since C++11). Most other languages offer regular expressions via a library.