use strict;
use warnings;

undef $/;
my $text = <DATA>;

my @result = map { m/'(.*?)'/g } grep /source/, split /\n/, $text;

use Data::Dumper;
print Dumper \@result;

__DATA__
'pfad'
source 'pfad2'
was soll passieren, wenn es 2 'pfade' 'gibt'? 
source 'pfad3' 'pfadX'
'pfad4' source
was ganz angeres
und 'nochwas' anderes

use 5.012;
use warnings;

my $text = <<EOF;
Hallo Welt!
Rhabarber mit 'Quark'
source '/sonst/wo'
oder auch anderes Zeug
'/wo/anders' source
Blubberdidu 'daddeldumm' kawumm
EOF

my @sources =
  map {
    if (/source/ && /'([^']*)'/) {
      ($1)
    } else {
      ()
    }
  }
  split /\n+/, $text;

say for @sources;

use 5.012;
use warnings;

my $text = <<EOF;
source '/foo/bar'
hollareiduljoeh
peng '/zack/bumm' source oder so
oans 'zwoa' dreie
EOF

my @lines;
my $pos = 0;
my $len = length $text;
while ($pos < $len) {
  my $sep = index $text, "\n", $pos;
  if ($sep >= 0) {
    push @lines, substr $text, $pos, $sep - $pos;
    $pos = $sep + 1;
  } else {
    push @lines, substr $text, $pos;
    $pos = $len;
  }
}

my @sources =
  map {
    my $start = index $_, "'";
    my $stop = index $_, "'", $start + 1;
    if (index($_, 'source') >= 0 and $start >= 0 and $stop >= 0) {
      (substr $_, ++$start, $stop - $start)
    } else {
      ()
    }
  }
  @lines;

say for @sources;