#!/usr/bin/env perl 
use strict;
use warnings;

my $data = 'unwanted_line1=blabla
unwanted_line2=blabla
my_variable=important_content_section1
important_content_section2
important_content_section3
unwanted_line3=blabla
';

my ($getVariable) = $data =~ /(my_variable=.*)^\w+=/sm;
print $getVariable;

##</code><code>##

#!/usr/bin/env perl 
use strict;
use warnings;

my $data = 'unwanted_line1=blabla
unwanted_line2=blabla
my_variable=important_content_section1
important_content_section2
important_content_section3
unwanted_line3=blabla
nonsense
unwanted_line4=blabla
whocansay
';

my ($getVariable) = $data =~ /(my_variable=.*?)^\w+=/sm;
print $getVariable;