Perl multiline regex for first 3 individual items - regex

Question

I am trying to read a regex format in Perl. Sometimes instead of a single line I also see the format in 3 lines.
For the below single line format I can regex as
/^\s*(.*)\s+([a-zA-Z0-9._]+)\s+(\d+)\s+(.*)/
to get the first 3 individual items in line
Hi There FirstName.LastName 10 3/23/2011 2:46 PM
Below is the multi-line format I see. I am trying to use something like
/^\s*(.*)\n*\n*|\s+([a-zA-Z0-9._]+)\s+(\d+)\s+(.*)$/m
to get individual items but don’t seem to work.
Hi There
FirstName-LastName 8 7/17/2015 1:15 PM
Testing - 12323232323 Hello There
Any suggestions? Is multi-line regex possible?
NOTE: In the same output i can see either Single line or Multi line or both so output can be like below
Hello Line1 FirstName.LastName 10 3/23/2011 2:46 PM
Hello Line2
Line2FirstName-LastName 8 7/17/2015 1:15 PM
Testing - 12323232323 Hello There
Hello Line3 Line3FirstName.LastName 8 3/21/2011 2:46 PM

Answer 1

You can for sure apply regex over multiple lines.
I've used the negated word \W+ between words to match space and newlines between words (actually \W is equal to [^a-zA-Z0-9_]).
The chat is viewed as a repetead \w+\W+ block.
If you provide more specific input / output case i can refine the example code:
#!/usr/bin/env perl
my $input = <<'__END__';
Hi There
FirstName-LastName 8 7/17/2015 1:15 PM
Testing - 12323232323 Hello There
__END__
my ($chat,$username,$chars,$timestamp) = $input =~ m/(?im)^\s*((?:\w+\W+)+)(\w+[-,\.]\w+)\W+(\d+)\W+([0-1]?\d\/[0-3]?\d\/[1-2]\d{3}\s+[0-2]?\d:[0-5]?\d\s?[ap]m)/;
$chat =~ s/\s+$//; #remove trailing spaces
print "chat -> ${chat}\n";
print "username -> ${username}\n";
print "chars -> ${chars}\n";
print "timestamp -> ${timestamp}\n";
Legenda
m/^.../ match regex (not substitute type) starting from start of line
(?im): case insensitive search and multiline (^/$ match start/end of line also)
\s* match zero or more whitespace chars (matches spaces, tabs, line breaks or form feeds)
((?:\w+\W+)+) (match group $chat) match one or more a pattern composed by a single word \w+ (letters, numbers, '_') followed by not words \W+(everything that is not \w including newline \n). This is later filtered to remove trailing whitespaces
(\w+[-,\.]\w+): (match group $username) this is our weak point. If the username is not composed by two regex words separated by a dash '-' or a comma ',' (UPDATE) or a dot '.' the entire regex cannot work properly (i've extracted both the possibilities from your question, is not directly specified).
(\d+): (match group $chars) a number composed by one or more digits
([0-1]?\d\/[0-3]?\d\/[1-2]\d{3}\s+[0-2]?\d:[0-5]?\d\s[ap]m): (match group $timestamp) this is longer than the others split it up:
[0-1]?\d\/[0-3]?\d\/[1-2]\d{3} match a date composed by month (with an optional leading zero), a day (with an optional leading zero) and a year from 1000 to 2999 (a relaxed constraint :)
[0-2]?\d:[0-5]?\d\s?[ap]m match the time: hour:minutes,optional space and 'pm,PM,am,AM,Am,Pm...' thanks to the case insensitive modifier above
You can test it online here

Answer 2

Your regex says:
^\s*(.*)\n*\n* # line starts with optional space followed by anything
| # or
\s+([a-zA-Z0-9._]+)\s+(\d+)\s+(.*)$ # spaces followed by any words followed by spaces, digits, spaces, anything at the end of the line
Consider this:
/^From|To$/
Alternation sticks as close to the sequences.
Above is really saying to find a line starting with 'Fro' followed by 'm' or 'T', followed by 'o', followed by the end of line
Compare to this:
/^(From|To)$/
Above will find lines that only have 'From' or 'To'