As suggested by Laurent R, you might consider using more Perl and less files and system commands.

If you like terse, you might try something like:

use strict;
use warnings;

my $cmd = "/usr/sbin/ntpq -p";
my $offset = (split(/\s+/, (grep(/^\*/, `$cmd`))[0]))[8];

print "$offset\n";
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If you find that a bit difficult to read and would prefer several statements with intermediate variables, you might try something like:

use strict;
use warnings;


my $cmd = "/usr/sbin/ntpq -p";

my @ntpout = `$cmd`;

my $current_time_source = (grep(/^\*/, @ntpout))[0];

my $offset = (split(/\s+/, $current_time_source))[8];

print "$offset\n";
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You should also think about what will happen if there are errors or unexpected situations. You might change the latter to something like:

use strict;
use warnings;

my $cmd = "/usr/sbin/ntpq -p";

my @ntpout = `$cmd`;
die "$cmd failed with: $^E, $?" unless(@ntpout);

my $current_time_source = (grep(/^\*/, @ntpout))[0];
die "Not synchronized" unless($current_time_source);

my $offset = (split(/\s+/, $current_time_source))[8];
die "$current_time_source: No offset" unless(defined($offset));

print "$offset\n";
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