Further to stevieb's remarks++ about properly understanding the context in which the  $fh filehandle is read in the OPed while-loop, note that if you had enabled strict at the start of your code, the code would not even have compiled due to the absence of an explicit declaration of a  @line array before using it. ($line[n] accesses the  @line array). So (all code examples untested)

use strict;

$filename = 'result.txt';

open( my $fh, '<', $filename ) or die "Can't open '$filename': $!";

while ( my $line = <$fh> ) {
    print "something here $line[0]";
    print "something here $line[1]";
    print "something here $line[2]";
    }

close $fh;
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would have failed to compile and would have thrown an error message about the undeclared  @line array that might have pointed you in the right debugging direction.

If a  @line array had, for some reason, been declared before the while-loop, there would have been no compile-time error, but the use of the warnings module would have produced a run-time warning (not an error | a fatal error) about the use of an uninitialized variable:

use strict;
use warnings;

$filename = 'result.txt';

open( my $fh, '<', $filename ) or die "Can't open '$filename': $!";

my @line;

while ( my $line = <$fh> ) {
    print "something here $line[0]";
    print "something here $line[1]";
    print "something here $line[2]";
    }

close $fh;
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The warning will have a source code line number associated with it which should aid in understanding the nature of the problem.

Bottom line: If you're a novice Perl programmer, always enable warnings and strict. If you're not a novice Perl programmer, then always enable warnings and strict — unless you have a very good and clearly understood reason not to do so.

Update: As hippo pointed out, we have Tutorials in the Monastery, and Use strict and warnings is a good one about strict (and warnings). See also the supplementary links at the end of the article.

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