in reply to Set the flag

It will be something like this, which turns $flag to 1 when it finds something: 
my $foo = "This is a test.";
my $flag = 0;
print "$flag\t$foo\n";
$flag = ($foo =~ s/a/the/);
print "$flag\t$foo\n";

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But like irah says, you need to provide some code or data if you want more specific help.

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Re^2: Set the flag
by Anonymous Monk on Nov 05, 2009 at 15:21 UTC 
    #!/usr/bin/perl
use strict;
use warnings;
my $flag=0;
while(<DATA>){
 if($flag == 0){
                if($_ =~ m/<p>/){
                $_ =~ s/<p>/<con>/;
                $flag=1;
                }
                }
print $_;

}
__DATA__
<root>
<p>This is para1</p>
<p>This is para2</p>
</root>

    [download]
    I have tried for the matching first <p>. But in a file how to find the last </p> tag and substitute.
    Please help me on this
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[d/l]
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In Section Seekers of Perl Wisdom