Invalid endpoint error on regular expression

Hello all, Using php 3.x, I'm trying to build a regular expression with data gathered from a submitted form. The code is in early days. Here it is: $dateMask = "$startMonth_[$startDay-$endDay]_$startYear"; $dateMask will be a string that looks something like this: 11_[12-18]_2000 Yet when I try to use $dateMask as a pattern for ereg: if(ereg($dateMask, $file)) $calendar[] = $file; I get a warning message that I've got an invalid endpoint in the range. Looks like a valid range to me. What am I missing? Thanks, Seth