Re: matching datetimestamps and concatenating data where timestamps match from multiple large datafiles

[CountZero]

For the "simple" case where you have all files in strict time-sequential order:

use Modern::Perl;

open my $FILEA, '<', './FILEA.TXT' or die $!;
open my $FILEB, '<', './FILEB.TXT' or die $!;
open my $FILEC, '<', './FILEC.TXT' or die $!;
open my $FILED, '<', './FILED.TXT' or die $!;

my $ts_B = 0;
my $ts_C = 0;
my $ts_D = 0;
while ( my $ts_A = <$FILEA> ) {
    chomp $ts_A;
    say "A:$ts_A matches B:$ts_B" if $ts_A == $ts_B;
    while ( $ts_B = <$FILEB> ) {
        chomp $ts_B;
        last if $ts_B > $ts_A;
        next if $ts_B < $ts_A;
        say "A:$ts_A matches B:$ts_B";
    }
    say "A:$ts_A matches C:$ts_C" if $ts_A == $ts_C;
    while ( $ts_C = <$FILEC> ) {
        chomp $ts_C;
        last if $ts_C > $ts_A;
        next if $ts_C < $ts_A;
        say "A:$ts_A matches C:$ts_C";
    }
    say "A:$ts_A matches D:$ts_D" if $ts_A == $ts_D;
    while ( $ts_D = <$FILED> ) {
        chomp $ts_D;
        last if $ts_D > $ts_A;
        next if $ts_D < $ts_A;
        say "A:$ts_A matches D:$ts_D";
    }
}

Output

A:102 matches B:102
A:264 matches C:264
A:403 matches D:403
A:403 matches D:403
A:560 matches D:560
A:560 matches D:560
A:744 matches B:744
A:744 matches B:744
A:827 matches C:827
A:915 matches D:915
A:915 matches D:915
A:1018 matches C:1018
A:1180 matches D:1180
...

The files I used don't have timestamps, just random numbers in an ever increasing sequence, but the logic remains the same.