By the sounds of your description, $sMatchPattern probably contains literal text rather than an actual regular expression pattern, or at least contains a literal \.

If you are searching for literal text, use the \Q and \E escapes to tell the regular expression engine to leave the text alone:

You also might be running into problems with escapes in your strings (which we could easily spot if you show your code!) For example:

my $oops = "\tell me something"; # <TAB>ell me something
my $ok   = '\tell me something'; # tell me something
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