bangers has asked for the wisdom of the Perl Monks concerning the following question:

How do I get grep to return the list of items in an array not matching a RE? 

my $bad = "NotMe!";

my @list = qw (one two three NotMe! four);

my @goodList = grep NOT /$bad/, @list;

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Re: grep items not matching an RE
by dave_the_m (Monsignor) on May 14, 2004 at 11:13 UTC
    Replace the NOT with a ! 
    my @goodList = grep !/$bad/, @list;

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[d/l]
      doh :-*

      Sorry I tried: 

      my @goodList = grep not /$bad/, @list;

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      I assumed that ! and NOT were the same. Does this work because ! has a different opperator precedence?
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[d/l]
        Does this work because ! has a different opperator precedence?
        Yes, 
        grep not /$bad/, @list;

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        is parsed as 
        grep not(/$bad/, @list);

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        since not has lower precedence than ,
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[d/l]
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      Hey, cool

      I always did that with my @goodList = grep {$_ !~ /$bad/} @list but your way looks a lot better, without the $_ thingy.
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[d/l]

        The EXPR version's also a good bit faster since it doesn't have to do the block enter/leave setup each item. 

        $ perl -MBenchmark=cmpthese -le 'cmpthese( 500_000, { BLOCK => sub { g
+rep { /a/ } qw( aa bb ab cd ef ) }, EXPR => sub { grep /a/, qw( aa bb
+ ab cd ef ) }, } )'
Benchmark: 
timing 500000 iterations of
 BLOCK, EXPR
...

     BLOCK: 16 wallclock secs (16.78 usr +  0.05 sys = 16.83 CPU) @ 29
+712.16/s (n=500000)

      EXPR:  4 wallclock secs ( 3.90 usr +  0.04 sys =  3.94 CPU) @ 12
+6984.13/s (n=500000)

          Rate BLOCK  EXPR
BLOCK  29712/s    --  -77%
EXPR  126984/s  327%    --

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[d/l]
Re: grep items not matching an RE
by Fletch (Bishop) on May 14, 2004 at 11:12 UTC

    The same way you reverse the sense of any other conditional. perldoc perlop, see ! and not.

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