open(my $fh, "<+", "your_file") or die("ack: $!");
my @data = <$fh>;
seek $fh, 0, 0;

my $newsize = 0;
for(@data) {
  next unless /\bsome string\b/;
  print $fh;
  $newsize += length;
}

truncate $fh, $newsize;
close $fh;
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open(my $read,  "<", "your_file") or die("ack: $!");
open(my $write, ">", "tmpfile$$") or die("ack: $!");

while(<$read>) {
  next unless /\b some string\b/;
  print $write;
}

close $read;
close $write;

rename $write, $read;
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_________
broquaint

while (my $line = readline STDIN) {
    # If the line matches the expression then skip the line.
    # Note the use of /x 
    if ( $line =~ /\b word \b/x ) {
        # Skip to the the next iteration
        next;
    }

    print $line;
}
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Save the code below to x.pl. Invoke with 'perl x.pl <filename>...'.

#!/usr/bin/perl -i -n
print unless /\bsome string\b/;
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