If you want to set up ORACLE_SID and ORACLE_HOME for the parent program, that will not work. It's impossible to set up environment variables for the calling program from a child.

The one thing you can do is output shell code which your parent then evaluates again via eval or . (depending on the shell).

In general, you should replace all instances of sed, awk and grep by s///, split and grep.

As an idiom, instead of writing grep -v grep|grep XXX, you can shorter write grep [X]XX.

Welcome to PerlMonks. No doubt you'll have seen the posting/formatting advice mentioned when posting, "Posts are HTML formatted...." How do I compose an effective node title?, How do I post a question effectively? and so on. In future please don't ignore this advice. You can update this post fixing these problems.

"we are not allow to install any package for PERL"

Yes, even you can use CPAN may be of interest to you. There is no such thing as PERL.

In your code you don't use strict;. I think you'd benifit from reading some basic perl tutorials. See also http://learn.perl.org

You are running sqlplus once, before setting environment variables, instead of running it once for each database with the environment variables set.

You are using shell syntax for passing STDIN to sqlplus. This doesn't work in Perl but you can use open and print to achieve a similar result. You can read open and perlipc for more on this.

Maybe something like the following would work better for you:

#!usr/bin/perl -w 
use strict;
use warnings;

my $c=`ps -ef |grep -v grep|grep pmon|sed -e 's/.*_//|sort -u >dbname.
+log`; 
my $cnt=`ps -ef |grep -v grep|grep pmon|sed -e 's/.*_//|sort -u |awk '
+END {print NR-0}'`; 

my $i=1; 
while($i<=$cnt) {
    my $dbn=`awk 'NR==$i' dbname.log`; 
    my $dbname = trim($dbn); 
    my $p=`cat /etc/oratab |grep $dbname|grep -v "#"|gawk -F: {print \
+$2'}`;
    $ENV{'ORACLE_SID'}="$dbname"; 
    $ENV{'ORACLE_HOME'}="$p"; 
    open(my $fh, '|-', 'sqlplus "/as sysdba"') or die "$!";
    print $fh "select name from v\$database;\nexit;\n";
    close($fh);
    $i++;
} 
exit 0; 

sub trim { 
    my $s = shift;
    $s =~s/^\s+|\s+$//g; 
    return $s; 
}
[download]

Edit: run sqlplus instead of cat