q prevents variable interpolation. So, $grep_date is not taking on the value 'Sep 02' inside your system call. It remains the literal string $grep_date. Try something like: 
my $cmd = 
    'cd /waslogs1/vfoneLog/cposapp && ls -lrt | grep -i "'
    . $grep_date
    . q(" | awk '{ print $9 }' > /home/cpos/CRM_Reports/output/filelis
+t.txt);
system $cmd;

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Also, system returns an exit status, not a command output. Look at qx.

In reply to Re: how to use perl variable in system command to run on unix by toolic
in thread how to use perl variable in system command to run on unix by tousifp

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