Question

I have array INPUTFILES with n files

INPUTFILES=( file_0 ... files_n-1 )

And i need to sort them in the array order by first row in files.

Files look like this:

2012.09.20 17:10
2012.11.21 00:10
2012.12.22 15:10
2012.12.23 15:10

I have already function to compare 2 files:

IsSooner () {
ONEFIRST=$( head -1 "${1}" ) 
ONELAST=$( tail -1 "${1}" )
TWOFIRST=$( head -1 "${2}" ) 
TWOLAST=$( tail -1 "${2}" )

TIMEFORMAT='Y.%m.%d %H:%M:'

perl <<EOF
use strict;
use warnings;

use Time::Piece;

open STDERR, "> /dev/null";

my @dates1 = ("${ONEFIRST}","${ONELAST}");
my @range1 = map Time::Piece->strptime("\$_", "${TIMEFORMAT}"), @dates1;

my @dates2 = ("${TWOFIRST}","${TWOLAST}");
my @range2 = map Time::Piece->strptime("\$_", "${TIMEFORMAT}"), @dates2;

if ( \$range1[0] < \$range2[0] ) {
  exit 0;
}

exit 1;
EOF

[ $? -eq 0 ] && {
  return 0
}

return 1  
}

Earlier will be first date in the file, the smaller index in the array will have.

Solution in BASH if preferable.

UPDATE
I don’t know format of date in advance. I just know it will be in strftime(3c) format.

Answer 1

1. In simple loop read first line of each file and save this information to hash, having first row data a hash key and the file name a hash value.

   my @inpufiles = ...;
   my %hash;
   foreach (@inputfiles) {
     open(my $fh, $_) or die $!;
     $hash{<$fh>} = $_;
     close $fh;
   }
   

2. Sort the hash by the keys and print all values of sorted hash.

   foreach (sort (keys(%hash))) {
     print "$hash{$_}\n";
   }
   

   If you don’t want to print it, just store it back to the array, then do just

   @inputfiles = map {$hash{$_}} sort (keys(%hash));
   

Good luck!

---

[UPDATE]

To follow the update in your question I suggest you to store values to hash using:

$hash{Time::Piece->strptime(<$fh>, $timeformat)->epoch} = $_;