Reformat Dates in Perl (for later use in MySQL) - perl

Question

I am writing a Perl script to open a .csv file, make some changes, sort it on four fields, then write it back to a new file. Found out that because this data will then be used to load a MySQL table that I also need to reformat the Date variables. Currently, Dates are in the file as 00/00/0000 and for MySQL, need to have them formatted as 0000-00-00. Right now, I simply tried to do it for one field, although I actually need to do it on three Date fields for each line from the .csv file.
This script is running - but it is not reformatting the Date field I'm trying to test this on.
#!/usr/bin/perl/
use strict;
use warnings;
use Data::Dumper;
#my $filename = '/swpkg/shared/batch_processing/mistints/mistints.csv';
my $filename = 'tested.csv';
open my $FH, $filename
or die "Could not read from $filename <$!>, program halting.";
# Read the header line.
chomp(my $line = <$FH>);
my #fields = split(/,/, $line);
#print "Field Names:\n", Dumper(#fields), $/;
print Dumper(#fields), $/;
my #data;
# Read the lines one by one.
while($line = <$FH>) {
# split the fields, concatenate the first three fields,
# and add it to the beginning of each line in the file
chomp($line);
my #fields = split(/,/, $line);
unshift #fields, join '_', #fields[0..2];
push #data, \#fields;
my $in_date = $fields[14];
my $db_date = join '-', reverse split /\D/, $in_date;
}
close $FH;
print "Unsorted:\n", Dumper(#data); #, $/;
#data = sort {
$a->[0] cmp $b->[0] ||
$a->[20] cmp $b->[20] ||
$a->[23] cmp $b->[23] ||
$a->[26] cmp $b-> [26]
} #data;
open my $OFH, '>', '/swpkg/shared/batch_processing/mistints/parsedMistints.csv';
#print $OFH Dumper(#data);
print $OFH join(',', #$_), $/ for #data;
close $OFH;
#print "Sorted:\n", Dumper(#data);
#print "Sorted:", Dumper(#data);
exit;
The two lines I added to this script (which are not working) are the my $in_date and my $db_date lines. Now I will also need to reformat two fields (at the end of each line) that are DATETIME, i.e. 10/23/2015 10:47, where I will only need to reformat the date within that field, and I'm not even sure where to begin tackling that one.
And please go easy since I'm a noob with Perl.
EDIT - SORRY, had to re-edit because I didn't notice the first part of my script had not copied.

Answer 1

Rather than using a bunch of string functions, it's better to use the Time::Piece module to parse and reformat date-time values. It has strptime and strftime methods to do this for you. This short program shows the reformatting of both date-time formats that you mention. ymd is a convenience method, and is equivalent to strftime('%Y-%m-%d')
use strict;
use warnings 'all';
use feature 'say';
use Time::Piece;
my $in_date = '01/02/2003';
my $db_date = Time::Piece->strptime($in_date, '%m/%d/%Y')->ymd;
say "$in_date -> $db_date";
$in_date = '01/02/2003 04:05';
$db_date = Time::Piece->strptime($in_date, '%m/%d/%Y %H:%M')->strftime('%Y-%m-%d %H:%M');
say "$in_date -> $db_date";
output
01/02/2003 -> 2003-02-01
01/02/2003 04:05 -> 2003-02-01 04:05
Update
If you prefer, you could write a subroutine that takes the original date and its format string, together with the desired format. Like this
use strict;
use warnings 'all';
use feature 'say';
use Time::Piece;
my $in_date = '01/02/2003';
my $db_date = date_from_to($in_date, '%m/%d/%Y', '%Y-%m-%d');
say "$in_date -> $db_date";
$in_date = '01/02/2003 04:05';
$db_date = date_from_to($in_date, '%m/%d/%Y %H:%M', '%Y-%m-%d %H:%M');
say "$in_date -> $db_date";
sub date_from_to {
my ($date, $from, $to) = #_;
Time::Piece->strptime($date, $from)->strftime($to);
}
The output is identical to that of the program above
Update
Regarding your comment, your code should look like this
$_ = join '-', (split /\//)[2,0,1] for $fields[14, 20, 23];
$_ = Time::Piece->strptime($_,'%m/%d/%Y %H:%M')->strftime('%Y-%m-%d %H:%M') for #fields[38,39];
push #data, \#fields;
But I would prefer to see some consistency in the way the date fields are handled, like this
$_ = Time::Piece->strptime($_, '%m/%d/%Y')->strftime('%Y-%m-%d') for #fields[14,20,23];
$_ = Time::Piece->strptime($_, '%m/%d/%Y %H:%M')->strftime('%Y-%m-%d %H:%M') for #fields[38,39];
push #data, \#fields