A possible solution for the cabeza.pl program is as follows:

cabeza.pl

#!/usr/bin/perl
 
# cabeza.pl - print the first 10 lines of a given file
 
use warnings;
use strict;
 
# This is the first argument on the command line
my $filename = shift(@ARGV);
 
# Check that file exists and is readable
unless (-r $filename)
{
    die "could not read file ($filename)";
}
 
open IN, "<$filename"
    or die "open($filename) $!";
 
my $lineno = 0;
while (<IN>)
{
    $lineno++;
    exit if ($lineno > 10);
 
    print;
}
 

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