system command ->no action

working_dir,system.pl --> uid=500 gid=100
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#!/usr/bin/perl
# Here is system.pl
use CGI;
$foo=new CGI;
print $foo->header;
# -- chdir is ok
$working_dir="/home/httpd/htdocs/webalizer/";
chdir($working_dir);
# -- mkdir no action
mkdir("html",0755); #-- no action
chown("500","100","html"); #-- no action
$temp1="-Q"; # -- first parameter
$temp2="/var/log/httpd/access_log"; #-- second parameter
@output=`webalizer $temp1 $temp2`; #-- no action
# --`cp * *` could be no action too
@output=`webalizer $temp2`;
print "@output<br>"; #--- output is ok,..but
# --but no any file created
# --if I chmod all exist files to -rw-r--rw(others)-
# --the exist files will be updated
@output=`ls`; #-- output is ok
print "<P>List files: @output<br>";
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# --if I chmod $working_dir to -rw-r--rw(others)-
# --no any file created too