thanks but it's not putting what i enter into terminal into that file.

Yes it does.

>perl a.pl
fasfd
dsfdasfdasf
dsafsdafdas
fdasfdasfs
^Z

>type perlogfile.rtf
fasfd
dsfdasfdasf
dsafsdafdas
fdasfdasfs
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Perhaps you are peeking at the file before you stop adding to it, in which case you are suffering from buffering. Fix:

#!/usr/bin/perl

use 5.010;

use strict;
use warnings;

use IO::Handle qw( );

my $fn_log = 'perlogfile.rtf';

open(my $fh_log, '>>', $fn_log)
    or die("Can't append to log file \"$fn_log\": $!\n");
$fh_log->autoflush(1);

print($fh_log $_) while <STDIN>;
[download]

fh = file handle

fn = file name. But it's actually used as a qualified file name, such as an absolute path (/foo/bar/file.txt) or a relative path (file.txt or baz/file.txt or ../qux/file.txt)