As others have already pointed out, the variable $text doesn't end in 'hello', so the substitution never occurs.

If you reorganized the program so that the data were read in from a file, or from a __DATA___ statement following the program, it works just fine, as so:

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

while (my $text = <DATA>) {
    $text =~ s/hello$//g;
    print $text; 
}
__DATA__
hello
world
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The output is:

~/perl/perlmonks$ ./nohello.pl

world
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