Added a Perl 5 script to update the leap-second tables in tai-utc.pm.

I tried to do it in Perl 6 first, but I couldn't get perl6-lwp-simple to work.

src/core/tai-utc.pm

@@ -1,7 +1,8 @@
 use v6;
 
 # This file keeps track of the differences between TAI and UTC
-# for internal use.
+# for internal use. The "BEGIN" and "END" comments are for
+# tools/update-tai-utc.pl.
 
 # Some handy tables:
 # http://tf.nist.gov/pubs/bulletin/leapsecond.htm
@@ -15,6 +16,7 @@ module tai-utc {
 
     # our @leap-second-dates = <
     our sub leap-second-dates() { <
+        #BEGIN leap-second-dates
         1972-06-30
         1972-12-31
         1973-12-31
@@ -39,6 +41,7 @@ module tai-utc {
         1998-12-31
         2005-12-31
         2008-12-31
+        #END leap-second-dates
     > };
 
     # our %leap-seconds =
@@ -50,30 +53,32 @@ module tai-utc {
 
     # Ambiguous POSIX times.
     our sub leap-second-posix() { <
+        #BEGIN leap-second-posix
           78796800
-          94694400 
-         126230400 
-         157766400 
-         189302400 
-         220924800 
-         252460800 
-         283996800 
-         315532800 
-         362793600 
-         394329600 
-         425865600 
-         489024000 
-         567993600 
-         631152000 
-         662688000 
-         709948800 
-         741484800 
-         773020800 
-         820454400 
-         867715200 
-         915148800 
-        1136073600 
-        1230768000 
+          94694400
+         126230400
+         157766400
+         189302400
+         220924800
+         252460800
+         283996800
+         315532800
+         362793600
+         394329600
+         425865600
+         489024000
+         567993600
+         631152000
+         662688000
+         709948800
+         741484800
+         773020800
+         820454400
+         867715200
+         915148800
+        1136073600
+        1230768000
+        #END leap-second-posix
     > };
 
 };

tools/update-tai-utc.pl

@@ -0,0 +1,47 @@
+#!/usr/bin/perl
+# Updates src/core/tai-utc.pm.
+
+use warnings;
+use strict;
+use Time::y2038 'timegm';
+use File::Slurp qw(slurp write_file);
+use LWP::Simple 'get';
+
+my $url = 'ftp://hpiers.obspm.fr/iers/bul/bulc/TimeSteps.history';
+
+$ARGV[0] or die "Please provide a path to src/core/tai-utc.pm.\n";
+my $tu_path = $ARGV[0];
+
+my @dates = do {
+    my @lines = split /\n/, get $url;
+    pop @lines;
+    shift @lines until $lines[0] =~ /\A 1972  Jul\.   1/;
+    map {
+        /(\d{4})  (Jan|Jul)/;
+        $2 eq 'Jan' ? [$1 - 1, 12, 31] : [$1, 6, 30]
+    } @lines
+};
+
+my $tu = slurp $tu_path;
+sub replace {
+    my ($find, $fmt, $f) = @_;
+    $tu =~ s
+        {^( *)#BEGIN $find\n.+?^ *#END $find\n}
+        { sprintf "$1#BEGIN $find\n%s\n$1#END $find\n", join "\n",
+              map { sprintf "%s$fmt", $1, $f->(@$_) } @dates }ems
+      or die "Couldn't replace $find";
+}
+replace 'leap-second-dates', '%d-%02d-%02d', sub { @_ };
+replace 'leap-second-posix', '%10d', sub {
+    my ($y, $m, $d) = @_;
+    1 + timegm 59, 59, 23, $d, $m - 1, $y - 1900;
+};
+write_file $tu_path, $tu;
+print "Updated.\n";
+
+# The IERS announces midyear leap seconds in early January and
+# end-of-year leap seconds in early July. So:
+
+my $month = (gmtime)[4];
+printf "This program should next be run in %s.\n",
+    1 < $month && $month < 8 ? 'August' : 'February';