$ echo 'line1 brown fox 
> line2 black owl 
> line3 red dear 
> ' | perl -ne 'print if /line\d+\s+\w+\s+(?!.*?fox)/' 
line2 black owl 
line3 red dear 
 
HP ~ 
$ echo 'line1 brown fox 
> line2 black owl 
> line3 red dear 
> ' | perl -ne 'print if /line\d+\s+.+(?!.*?fox)/' 
line1 brown fox 
line2 black owl 
line3 red dear

$ echo 'line1 brown fox 
> line2 black owl 
> line3 red dear 
> '  | perl -ne 'print "$1\n"  if /(line\d+\s+.+?)(?!.*?fox)/' 
line1 brown f 
line2 b 
line3 r

 
#!/usr/bin/perl 
use strict; 
use warnings; 
 
my $re1 = '(?=.+fox)^line.+$'; 
my $re2 = '(?!.+fox)^line.+$'; 
 
for my $re ($re1, $re2) { 
	print "\tUsing regular expression $re\n"; 
	while (<DATA>) { 
		print if /$re/;	 
	} 
	seek DATA, 0, 0; 
	print "\n\n"; 
} 
 
__DATA__ 
line1 brown fox  
line2 black owl  
line3 red dear  

C:\Old_Data\perlp>perl test2.pl 
        Using regular expression (?=.+fox)^line.+$ 
line1 brown fox 
 
 
        Using regular expression (?!.+fox)^line.+$ 
line2 black owl 
line3 red dear

Compiling REx "(line.*)(?!.*fox)" 
Final program: 
   1: OPEN1 (3) 
   3:   EXACT <line> (5) 
   5:   STAR (7) 
   6:     REG_ANY (0) 
   7: CLOSE1 (9) 
   9: UNLESSM[0] (17) 
  11:   STAR (13) 
  12:     REG_ANY (0) 
  13:   EXACT <fox> (15) 
  15:   SUCCEED (0) 
  16: TAIL (17) 
  17: END (0) 
anchored "line" at 0 (checking anchored) minlen 4 
Guessing start of match in sv for REx "(line.*)(?!.*fox)" against "line1 brown fox" 
Found anchored substr "line" at offset 0... 
Guessed: match at offset 0 
Matching REx "(line.*)(?!.*fox)" against "line1 brown fox" 
   0 <> <line1 brow>         |  1:OPEN1(3) 
   0 <> <line1 brow>         |  3:EXACT <line>(5) 
   4 <line> <1 brown fo>     |  5:STAR(7) 
                                  REG_ANY can match 11 times out of 2147483647... 
  15 <e1 brown fox> <>       |  7:  CLOSE1(9) 
  15 <e1 brown fox> <>       |  9:  UNLESSM[0](17) 
  15 <e1 brown fox> <>       | 11:    STAR(13) 
                                      REG_ANY can match 0 times out of 2147483647... 
                                      failed... 
  15 <e1 brown fox> <>       | 17:  END(0) 
Match successful! 
Freeing REx: "(line.*)(?!.*fox)"

#!/usr/bin/perl 
use strict; 
use warnings; 
use re qw/debug/; 
 
$_ = 'line1 brown fox'; 
/(line.*)(?!.*fox)/;

#!/usr/bin/perl 
use strict; 
use warnings; 
 
my $re1 = '^(line.*fox)$'; # no look-around assertions needed 
my $re2 = '^(line.*$)(?<!fox)'; 
 
for my $re ($re1, $re2) { 
	print "\tUsing regular expression $re\n"; 
	while (<DATA>) { 
		print "$1\n" if /$re/;	 
	} 
	seek DATA, 0, 0; 
	print "\n"; 
} 
 
__DATA__ 
line1 brown fox 
line2 black owl 
line3 red dear

  DB<1> $_ = "tip top"; 
 
  DB<2> print "true\n" if /tip/; 
true 
 
  DB<3>  print "true\n" if /tip(?!top)/ 
true 
 
  DB<4> print "true\n" if /tip.(?!top)/ 
 
  DB<5> print "true\n" if /tip.+(?!top)/ 
true 
 
  DB<6> print $1 if /(tip.+)(?!top)/; 
tip top 
  DB<7>  print $1 if /(tip.+?)(?!top)/; 
tip t

use strict; 
use warnings; 
my @tests = ( 
    "line1 brown fox\n", 
    "line2 black owl\n", 
    "line3 red dear\n", 
);     
print "Positive lookahead\n"; 
foreach (@tests) { 
    print if /line(?=.*fox)/;  
} 
print "Negative lookahead\n"; 
foreach (@tests) { 
    print if /line(?!.*fox)/;  
}

  DB<1> $_ = "line1 brown fox\n"; 
 
  DB<2> print if /line\d+\s+\w+\s+(?!fox)/; 
 
  DB<3> print if /line\d+\s+\w+.+(?!fox)/;  
line1 brown fox 
 
  DB<4>  print if /line\d+\s+\w+\s+(?!fix)/; 
line1 brown fox

use strict; 
use warnings; 
use Test::Simple tests => 6; 
 
my $REGEX_POS = qr/ line (?=.*fox) /x; 
my $REGEX_NEG = qr/ line (?!.*fox) /x; 
 
$_ = "line1 brown fox\n"; 
ok(  /$REGEX_POS/, 'Positive lookahead Match'); 
ok( !/$REGEX_NEG/, 'Negative lookahead No-Match'); 
 
$_ = "line2 black own\n"; 
ok( !/$REGEX_POS/, 'Positive lookahead No-Match'); 
ok(  /$REGEX_NEG/, 'Negative lookahead Match'); 
 
$_ = "line3 red dear\n"; 
ok( !/$REGEX_POS/, 'Positive lookahead No-Match'); 
ok(  /$REGEX_NEG/, 'Negative lookahead Match');

1..6 
ok 1 - Positive lookahead Match 
ok 2 - Negative lookahead No-Match 
ok 3 - Positive lookahead No-Match 
ok 4 - Negative lookahead Match 
ok 5 - Positive lookahead No-Match 
ok 6 - Negative lookahead Match

perl -ne 'print if /(line.*)(?!.*fox)/' text.txt