Re: How do I delete from a delimiter to the end of a file?

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Re^2: How do I delete from a delimiter to the end of a file? by JavaFan (Canon) on Aug 25, 2008 at 12:51 UTC
.? usually comes with a speed penalty (unless the optimizer eliminates running .? at all), as Perl needs to do bookkeeping for possible backtracking. I'd write it as: `s/------ Yahoo[^\cb]+//g; # Keeps the ^B s/------ Yahoo[^\cb]+\cB//; # Removes the ^B as well.` [download]	[reply] [d/l]
Re^3: How do I delete from a delimiter to the end of a file? by ikegami (Patriarch) on Aug 25, 2008 at 20:34 UTC
I don't know from where you got your information, but it appears to be incorrect. `Rate JavaFan JavaFan_noplus ikegami JavaFan 104/s -- -5% -16% JavaFan_noplus 109/s 5% -- -12% ikegami 123/s 19% 13% -- Rate JavaFan JavaFan_noplus ikegami JavaFan 109/s -- -2% -11% JavaFan_noplus 110/s 2% -- -10% ikegami 122/s 13% 11% -- Rate JavaFan JavaFan_noplus ikegami JavaFan 103/s -- -5% -21% JavaFan_noplus 109/s 5% -- -17% ikegami 131/s 27% 20% --` [download] Read more... (1117 Bytes)	[reply] [d/l] [select]
Re^4: How do I delete from a delimiter to the end of a file? by JavaFan (Canon) on Aug 26, 2008 at 06:41 UTC
That surprises me, and I wonder why .? is somewhat faster than a more explicite pattern. However, I'd still shy away from using .?. Consider the effect of a slight change of the string we are matching against (basically, replacing the \cB with \cA): use Benchmark qw( cmpthese ); my $ad = <<'__EOI__'; ------ Yahoo meow meow meow meow meow meow meow meow woof woof woof woof jabberwocky foo bar! foo!! __EOI__ my $email = join '', map chr(rand(26)+ord('a')), 1..2000; our $file = "$email\n$ad\cA" x 1000; cmpthese(-3, { ikegami => 'use strict; use warnings; my $x = our $file; $x +=~ s/----- - Yahoo.?(?=\cB)//sg;', JavaFan => 'use strict; use warnings; my $x = our $file; $x +=~ s/----- - Yahoo[^\cB]+//g;', JavaFan_noplus => 'use strict; use warnings; my $x = our $file; $x +=~ s/----- - Yahoo[^\cB]*//g;', }); __END__ (warning: too few iterations for a reliable count) Rate ikegami JavaFan JavaFan_noplus ikegami 0.264/s -- -98% -98% JavaFan 16.2/s 6053% -- -1% JavaFan_noplus 16.5/s 6135% 1% -- [download]	[reply] [d/l]

I'd write it as:

   s/------ Yahoo[^\cb]*+//g;    # Keeps the ^B
   s/------ Yahoo[^\cb]*+\cB//;  # Removes the ^B as well.
[download]

[reply]
[d/l]

I don't know from where you got your information, but it appears to be incorrect.

                Rate        JavaFan JavaFan_noplus        ikegami
JavaFan        104/s             --            -5%           -16%
JavaFan_noplus 109/s             5%             --           -12%
ikegami        123/s            19%            13%             --

                Rate        JavaFan JavaFan_noplus        ikegami
JavaFan        109/s             --            -2%           -11%
JavaFan_noplus 110/s             2%             --           -10%
ikegami        122/s            13%            11%             --

                Rate        JavaFan JavaFan_noplus        ikegami
JavaFan        103/s             --            -5%           -21%
JavaFan_noplus 109/s             5%             --           -17%
ikegami        131/s            27%            20%             --
[download]

Read more... (1117 Bytes)

[reply]
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However, I'd still shy away from using .*?. Consider the effect of a slight change of the string we are matching against (basically, replacing the \cB with \cA):

 
use Benchmark qw( cmpthese );
   
my $ad = <<'__EOI__';
------ Yahoo
meow meow meow meow meow meow meow meow
woof woof woof woof
jabberwocky
foo bar! foo!!
__EOI__
 
my $email = join '',
            map chr(rand(26)+ord('a')),
            1..2000;
 
 
our $file = "$email\n$ad\cA" x 1000;
cmpthese(-3, {
   ikegami        => 'use strict; use warnings; my $x = our $file; $x 
+=~ s/-----
- Yahoo.*?(?=\cB)//sg;',
   JavaFan        => 'use strict; use warnings; my $x = our $file; $x 
+=~ s/-----
- Yahoo[^\cB]*+//g;',
   JavaFan_noplus => 'use strict; use warnings; my $x = our $file; $x 
+=~ s/-----
- Yahoo[^\cB]*//g;',
});
__END__
            (warning: too few iterations for a reliable count)
                  Rate        ikegami        JavaFan JavaFan_noplus
ikegami        0.264/s             --           -98%           -98%
JavaFan         16.2/s          6053%             --            -1%
JavaFan_noplus  16.5/s          6135%             1%             --
[download]

[reply]
[d/l]