Perl regular expression {} quantifier multiple matches - regex

Question

Im trying to parse a file wherein each line has 3 floats(1, +1.0 -1.0 being valid values) and while the regular expression in the snippet matches a float value, I'm not sure how I should be using the Perl quantifier {n} to match multiple floats within a single line.
#!/usr/bin/perl
use strict;
use warnings;
open(my $fh, "<", "floatNumbers.txt") or die "Cannot open < floatNumbers.txt";
while(<$fh>)
{
if ($_=~m/([-+]?\d*[\.[0-9]*]?\s*)/)
{
print $1."\n";
}
}
Code snippet, I tried to match 3 floats within a line. Could readers help me with the correct usage of the {} quantifier?
if ($_=~m/([-+]?\d*[\.[0-9]*]?\s*){3}/)

Answer 1

You're trying to do extraction and validation at the same time. I'd go with:
sub is_float {
return $_[0] =~ /
^
[-+]?
(?: \d+(?:\.[0-9]*)? # 9, 9., 9.9
| \.[0-9]+ # .9
)
\z
/x;
}
while (<$fh>) {
my #fields = split;
if (#fields != 3 || grep { !is_float($_) } #fields) {
warn("Syntax error at line $.\n");
next;
}
print("#fields\n");
}
Note that your validation consdered ., [ and ...0...0... to be numbers. I fixed that.

Answer 2

Quntifiers just allow you to specify how many times you want to match something in a regex.
For example /(ba){3}/ would match ba in a string exactly 3 times :
bababanfnfd = bababa but not
baba = no match.
You can also use (taken from: http://perldoc.perl.org/perlrequick.html):
a? = match 'a' 1 or 0 times
a* = match 'a' 0 or more times, i.e., any number of times
a+ = match 'a' 1 or more times, i.e., at least once
a{n,m} = match at least n times, but not more than m times.
a{n,} = match at least n or more times
a{n} = match exactly n times

Answer 3

This is a generalized pattern that I think does what you are talking about:
# ^\s*(?:[-+]?(?=[^\s\d]*\d)\d*\.?\d*(?:\s+|$)){3}$
^ # BOL
\s* # optional whitespaces
(?: # Grouping start
[-+]? # optional -+
(?= [^\s\d]* \d ) # lookahead for \d
\d* \.? \d* # match this form (everything optional but guaranteed a \d)
(?: \s+ | $ ) # whitespaces or EOL
){3} # Grouping end, do 3 times
$ # EOL