The following method stores the lines you wish to print in a hash as an action table^tm. This allows for a fairly simple approach to reading the second text file, and deciding line by line whether to print or not. This method is fairly efficient:

use strict;
use warnings;


my %find;
open INDEX, '<', shift( @ARGV ) or die $!;
while( <INDEX> ) {
    @find{ $_ .. $_ + 2 } = ();
}
close INDEX;
    


while( <> ) {
    next unless exists $find{$.};
    print $_;
    delete $find{$.};
    last unless keys %find;
}
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Advantages:

• The script won't error-out if you request an index beyond the end of the text file.
• Overlap is fine. Requesting lines 1, 2, and 4 will print 1, 2, 3, 4, 5, 6, not 1, 2, 2, 3, 4, 4, 5, 6.
• There's no need to sort the line index list.
• Terminates the search once there are no more indices in the list.

The above code is "one liner friendly", and can be expressed like this:

perl -ne "BEGIN{open I, '<', shift(@ARGV); while(<I>){ @find{$_ .. $_+
+2}=();}} next unless exists $find{$.}; print; delete $find{$.} last u
+nless keys %find;"
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