UNIX has `head` and `tail`, but what about when you need a line number in the middle? `mid` provides just that.

mid

#!/usr/bin/perl

# Returns the requested line number from a file or list of files.
# If the line number is given as i:j or i-j, selects that range.
# If no file is given, we read from STDIN.

my $arg = shift;
($num1,$split,$num2) = split(/([:\-\+])/,$arg);
die usage() unless $arg and (! $split or $num2);

my $i = $num1;
my $j = ($split)
        ? ( ($split eq "+") ? ($num1 + $num2) : ($num2) )
        : $num1;

exit usage() unless $i > 0;

if (@ARGV > 1) {
  # if multiple files are given, recurse to calling mid on each one
  map { system("$0 $i $_") } @ARGV;
} else {
  # else, just print the ith line
  while (my $line = <>) {
    next if $. < $i;
    print $line;
    last if $. >= $j;
  }
}

sub usage() {
  print STDERR <<EOF;
Usage: 
    mid LINENO FILE1 [FILE2 FILE3 ...]
    cat FILE | mid LINENO
where LINENO is the line number of the file (starting with 1).
EOF
  exit(1);
}