thanks anonymous ,
i changed accordingly as they mentioned previously with $! then am getting error as following
Software error:
: Cannot make directory /var/www/html/piRNA_html/UNAFold/output/10010
errorwas:Permission denied at /var/www/html/piRNA_html/UNAFold/unafold.cgi line 55.
i couldnt understand , y permission denied, though i gave 777 permission in the code, please let me know abt this