Find the time difference (if it does not exceed 24 hours)

Perl
Date/Time

To find the time difference, you first need to convert what is labeled hhmmss to seconds. After finding the difference in seconds, restore to the time representation of hhmmss again. This is an example to find the time difference.

use strict;
use warnings;

print "(1) Find the time difference (does not exceed 24 hours)\n";
my $time_str1 = '03:44:23';
my $time_str2 = '22:34:45';

# Convert the time string representation to a hash of time information.
my $time1 = time_from_str ($time_str1);
my $time2 = time_from_str ($time_str2);

# Convert time information hash to seconds to calculate elapsed seconds
my $sec_interval = time_to_sec ($time2) - time_to_sec ($time1);

# Convert elapsed seconds to hash of time representation
my $time_interval = sec_to_time($sec_interval);

# Convert time representation hash to time string representation
my $time_interval_str = str_from_time($time_interval);

print "Time difference is $time_interval_str.\n";

# A function that converts a string representation of time into a hash that represents time information
sub time_from_str {
  my $time_str = shift;
  return unless $time_str;
  
  my $time = {};
  if ($time_str =~ /^(\d{2}): (\d{2}) :(\d{2})$/) {
    @{$time}{qw/hour min sec /} = ($1, $2, $3);
    return wantarray?%$time: $time;
  }
  return;
}

# A function that converts a hash representing time information into a string representation of time.
sub str_from_time {
  my $time;
  if (ref $_[0] eq 'HASH') {
    $time = shift;
  }
  else {
    %$time = @_;
  }
    
  return unless defined $time->{hour};
  return unless defined $time->{min};
  return unless defined $time->{sec};
    
  my $time_str
    = sprintf("%02s:%02s:%02s", @{$time}{qw/hour min sec /});
  return $time_str;
}

# Function to convert time to seconds
sub time_to_sec {
  my $time;
  if (ref $_[0] eq 'HASH') {
    $time = shift;
  }
  else {
    %$time = @_;
  }
    
  return unless defined $time->{hour};
  return unless defined $time->{min};
  return unless defined $time->{sec};
  
  my $sec = $time->{hour} * 3600 +
            $time->{min} * 60 +
            $time->{sec};
  
  return $sec;
}

# A function that converts seconds to time.
sub sec_to_time {
  my $sec = int(shift);
  my $time = {};
  
  $time->{hour} = int($sec/3600);
  $sec = $sec % 3600;
  
  $time->{min} = int($sec/60);
  $sec = $sec % 60;
  
  $time->{sec} = $sec;
  
  return wantarray?%$time: $time;
}

Output

(1) Find the time difference (does not exceed 24 hours)
The time difference is 18:50:22.

Code explanation

Convert time string representation to hash representing time information

If the time is displayed in the log etc., it is a string. It is convenient to convert this string into a hash that represents the time information.

It's common to convert strings to hashes in this way. (Structuring the data increases abstraction, readability, and reusability.)

# Convert the time string representation to a hash of time information.
my $time1 = time_from_str ($time_str1);
my $time2 = time_from_str ($time_str2);

# A function that converts a string representation of time into a hash that represents time information
sub time_from_str {
  my $time_str = shift;
  return unless $time_str;
  
  my $time = {};
  if ($time_str =~ /^(\d{2}): (\d{2}) :(\d{2})$/) {
    @{$time}{qw/hour min sec /} = ($1, $2, $3);
    return wantarray?%$time: $time;
  }
  return;
}

The following part is a hash slice. It is a form of dereferencing $time and assigning it as a hash slice. qw is a string list operator.

@{$time}{qw/hour min sec /} = ($1, $2, $3);

The return value allows you to select a list and a scalar.

return wantarray?%$time: $time;

Convert the hash of time information to seconds and calculate the elapsed seconds

The calculation to convert the time to seconds is "hours x 3600 + minutes x 60 + seconds".

my $sec_interval = time_to_sec ($time2) - time_to_sec ($time1);

# Function to convert time to seconds
sub time_to_sec {
  my $time;
  if (ref $_[0] eq 'HASH') {
    $time = shift;
  }
  else {
    %$time = @_;
  }
    
  return unless defined $time->{hour};
  return unless defined $time->{min};
  return unless defined $time->{sec};
  
  my $sec = $time->{hour} * 3600 +
            $time->{min} * 60 +
            $time->{sec};
  
  return $sec;
}

Convert elapsed seconds to hash of time representation

To convert seconds to time, find the quotient and remainder of seconds divided by 3600. This quotient becomes "time".

Then find the quotient and the remainder by dividing the remainder by 60. This quotient is "minutes" and the remainder is "seconds".

my $time_interval = sec_to_time($sec_interval);

# A function that converts seconds to time.
sub sec_to_time {
  my $sec = int(shift);
  my $time = {};
  
  $time->{hour} = int($sec/3600);
  $sec = $sec % 3600;
  
  $time->{min} = int($sec/60);
  $sec = $sec % 60;
  
  $time->{sec} = $sec;
  
  return wantarray?%$time: $time;
}

Convert time representation hash to time string representation

Finally, it returns to the string again. Here, I used the sprintf function.

my $time_interval_str = str_from_time($time_interval);

# A function that converts a hash representing time information into a string representation of time.
sub str_from_time {
  my $time;
  if (ref $_[0] eq 'HASH') {
    $time = shift;
  }
  else {
    %$time = @_;
  }
    
  return unless defined $time->{hour};
  return unless defined $time->{min};
  return unless defined $time->{sec};
    
  my $time_str
    = sprintf("%02s:%02s:%02s", @{$time}{qw/hour min sec /});
  return $time_str;
}

Perl ABC