Passing PHP variables to shell program through shell_exec

I need to convert multiple ksh based .cgi files to php.  The shell_exec function appears to be just what I'm looking for since I need to utilize the standard shell tools like grep and awk.
It seems to work for me if I hard code what I'm looking for but doesn't recognize a variable passed from the PHP script:

This is a piece of script provided by liveaspankaj last year.  It has been modified to my needs.  The major issue is the $memberid variable is not recognized by grep.  Hardcoding the memberid works.  Quotes or no quotes are irrelevent.  I need to know how to enter the variable name so grep ( or any other program ) called by shell_exec can recognize it.
Also, pipeing ithe results to awk like this results in the entire record being displayed instead of the first field.  If I can get these two issues resolved, it will be a big step in getting all my files re-written and  i would be extremely grateful.


$output = shell_exec('grep "$memberid" MembersOnly/members.csv | awk -F, "{print $1}" | head -1');