use strict;
use warnings;

sub date {
    my @d = localtime (shift || time);
    sprintf "%4d-%02d-%02d %02d:%02d:%02d", $d[5] + 1900, ++$d[4], @d[3,2,1,0];
    } # date

open my $fi, "<", "C:/Users/li/perl/part1.txt" or die "File not found";
open my $fo, ">", "C:/Users/li/perl/part1_CORRECTED.txt" or die "Cannot create output: $!";

while (<$fi>) {
    s/\b([0-9]{10})\b/date ($1)/ge;
    print $fo $_;
    }
close $fi or die $!;
close $fo or die $!;