Thank you hippo

After surrounding that with variable definitions, file paths, file open/close and prints to a new file in a Perl script, I am a VERY HAPPY CAMPER.

Not sure how it works; will explore that.

Forgot to log in, RobertJ. Again thanks.

Be aware that you might not be such a happy camper if the times fall within the hour after midnight! That code matches and captures, in the special variable $1, the two digits following a space, i.e. the hour value. It then executes (e modifier) the sprintf command in the substitution to replace the hour with a decremented value ($1 - 1). The q{ %2.2i} is the format specifier; q{ %02d} would also work. This method will break down if the hour is zero.

The simple way.

$ perl -Mstrict -Mwarnings -E '
my $dateStr = q{2016-05-16 00:51:07};
$dateStr =~ s{ (\d\d)}{ sprintf q{ %2.2i}, $1 - 1 }e;
say $dateStr;'
2016-05-16 -01:51:07
$
[download]

A little more robust.

$ perl -MTime::Piece -MTime::Seconds -Mstrict -Mwarnings -E '
my $dateStr = q{2016-05-16 00:51:07};
my $dateFmt = q{%Y-%m-%d %H:%M:%S};
my $tp      = Time::Piece->strptime( $dateStr, $dateFmt );
$tp        -= ONE_HOUR;
say $tp->strftime( $dateFmt );'
2016-05-15 23:51:07
$
[download]

I hope this is of interest.

Cheers,

JohnGG

OK I have been looking at that statement

$stuff =~ s/ (\d\d)/sprintf(" %2.2i",$1-1)/e;

I have poured over my Perl O'Reilly book and am still clueless. Since the input lines look like this

2016-05-16 10:51:07 random text

How does the expression pick out the hours versus any other two digits?

Then what does the sprintf do? I'm willing to learn but would need a starting point.