Perl Merge file

Question

I have 3 or multiple files I need to merge, the data looks like this..

file 1
0334.45656
0334.45678
0335.67899
file 2
0334.89765
0335.12346
0335.56789
file 3         


        

Answer 1

I suggest this solution, which uses a sorted array of hashes - each hash corresponding to an input file, and containing a file handle fh, the last line read line and the timestamp extracted from the line timestamp.

The hash at the end of the array always corresponds to the input that has the smallest value for the timestamp, so all that is necessary is to repeateedly pop the next value from the array, print its data, read the next line and (if it hasn't reached eof) insert it back into the array in sorted order.

This could produce an appreciable increase in speed over the repeated sorting of all the data for each output line that other answers use.

Note that the program expects the list of input files as parameters on the command line, and sends its merged output to STDOUT. It also assumes that the input files are already sorted.

use strict;
use warnings;
use autodie;

my @data;

for my $file (@ARGV) {
  my $item;
  open $item->{fh}, '<', $file;
  insert_item($item, \@data);
}

while (@data) {
  my $item = pop @data;
  print $item->{line};
  insert_item($item, \@data);
}

sub insert_item {
  my ($item, $array) = @_;
  return if eof $item->{fh};
  $item->{line} = readline $item->{fh};
  ($item->{timestamp}) = $item->{line} =~ /^(\d+)/;
  my $i = 0;
  ++$i while $i < @$array and $item->{timestamp} < $array->[$i]{timestamp};
  splice @$array, $i, 0, $item;
}

output

0334.45656
0334.89765
0334.12345
0334.45678
0335.12346
0335.45678
0335.67899
0335.56789
0335.98764