string parsing in perl

Question

I need some help on string parsing in perl. I've an http server that respond with something like this:

<html>
<head><title></title></head><body>
T:17.10;H:32.10
</body></html>

I need to catch the two numbers (in the example 17.10 and 32.10) and put them in two variables that I will use for do some if...then...else cycle.

I'm not so expert in string manipulation and regex, at the moment I'm tring to do this:

my $url = 'http://192.168.25.9';
my $content = get $url;
die "Couldn't get $url" unless defined $content;
my @lines = split /\n/, $content;
$content2 = $lines[2];
$content2 =~ tr/T://d;
$content2 =~ tr/H://d;
my @lines2 = split /;/, $content2;
$tem = $lines2[0];
$hum = $lines2[1];

$tem =~ m{(\d+\.\d+)};
$hum =~ m{(\d+\.\d+)};

but when I print out the line I see something strange: characters missing, space in the line, etc. It seems that I've some strange invisible characters that create confusion.

Could you suggest me a better way for have the two number in two numeric variables?

Thanks Fabio

Which variables are you printing and what are you seeing? Use Data::Dumper to display the content of your variables. — René Nyffenegger
– René Nyffenegger, Commented Jan 13, 2015 at 18:51
How are you getting the html? Which module does get come from. — TLP
– TLP, Commented Jan 13, 2015 at 19:59

Community · Accepted Answer · 2017-05-23 10:25:23Z

6

A complete solution, avoiding parsing HTML with REGEX (ref: RegEx match open tags except XHTML self-contained tags ) :

use strict; use warnings;

# base perl module to fetch HTML
use LWP::UserAgent;
# base perl module to parse HTML
use HTML::TreeBuilder;

# fetching part
my $ua = LWP::UserAgent->new;
my $req = HTTP::Request->new(GET => "http://192.168.25.9");
my $res = $ua->request($req);
die $res->status_line, "\n" unless $res->is_success;

# parsing part
my $tree = HTML::TreeBuilder->new();
# get text from HTML
my $out = $tree->parse($res->decoded_content)->format;
# extract the expected string from the text output
if ($out =~ /^\s*T:(\d{2}\.\d{2});H:(\d{2}\.\d{2}).*/) {
    print join "\n", $1, $2;
}

OUTPUT:

17.10
32.10

edited May 23, 2017 at 10:25

CommunityBot

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answered Jan 13, 2015 at 18:52

Gilles Quénot

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1 Comment

Borodin Over a year ago

I don't see any point in involving HTML::TreeBuilder at all -- certainly not just for the purpose of formatting the HTML. It would also be wise to use decoded_content instead of content, as you don't know whether the HTTP content is compressed.

red0ct · Accepted Answer · 2015-01-13 22:07:26Z

2

Specifically for such requests you can do so:

my ($t, $h) = map { (/T:(\d+|\d+.\d+);H:(\d+|\d+.\d+)/)?($1, $2):() } @req;
print "$t, $h\n", $t * $h;

Output:

17.10, 32.10
548.91

where @req is an array with chomped strings of the received request

edited Jan 13, 2015 at 22:07

answered Jan 13, 2015 at 19:57

red0ct

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2 Comments

Borodin Over a year ago

This solution seems fine to me, and I don't understand the downvote. The other solutions go into a lot of unnecessary work to format or strip the HTML, which is entirely unnecessary unless you wanted to ensure that the required text is the sole content of the <body> element, which none of them do. Your regex is a little naive though, as I think there is a good chance that the numeric values may look like 123.4 or 2.8896, or even 42, and your pattern will match none of these.

red0ct Over a year ago

Thanks for the support, Borodin. Agree with your comments. Fixed regexp. Perhaps now it's more flexible.

Ben Grimm · Accepted Answer · 2015-01-14 21:48:41Z

1

For your purpose, this is all you need:

my ($tem, $hum) = $content =~ /T:(\d{2}\.\d{2});H:(\d{2}\.\d{2})/;

If you need more general parse (e.g. to support a temperature or humidity >= 100, single digit values, etc...):

my ($tem, $hum) = $content =~ /T:(\d+(?:\.\d+)?);H:(\d+(?:\.\d+)?)/;

edited Jan 14, 2015 at 21:48

answered Jan 13, 2015 at 20:48

Ben Grimm

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2 Comments

Borodin Over a year ago

I don't see any need to remove the HTML markup. The data is either there or it is not, although I guess there is an infinitesimal chance that a false match could be found in the value of one of the attributes.

Ben Grimm Over a year ago

That's true, he's not really parsing html here. The answer just comes down to the one line: my ($tem, $hum) = $content =~ /T:(\d{2}.\d{2});H:(\d{2}.\d{2})/;

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