comment on

I'd seen Tie::File touted recently, so I decided to see how it stood up. I added the following subroutine:

sub tie_file {
  my @lines;
  tie @lines, 'Tie::File', $file or die "$!";
  map {"$_\n"} @lines[-$limit..-1];
}
[download]

Pretty much as simple as it gets. Unfortunatly, it's not quite so hot on the performance:

[chmrr@supox chmrr]$ wc -l /var/log/messages
   4442 /var/log/messages
[chmrr@supox chmrr]$ perl -w tailbm.pl -10 100 /var/log/messages
Benchmark: running f_rb_obj, f_rb_obj_u, f_rb_tie, f_rb_tie_u, file_ta
+il, grinder, lastn, lastn_getc, tie_file, each for at least 10 CPU se
+conds...
  f_rb_obj: 11 wallclock secs (10.35 usr +  0.22 sys = 10.57 CPU) @ 66
+2.54/s (n=7003)
f_rb_obj_u: 11 wallclock secs (10.54 usr +  0.12 sys = 10.66 CPU) @ 65
+0.19/s (n=6931)
  f_rb_tie: 11 wallclock secs (10.48 usr +  0.20 sys = 10.68 CPU) @ 54
+5.13/s (n=5822)
f_rb_tie_u: 12 wallclock secs (10.39 usr +  0.16 sys = 10.55 CPU) @ 53
+7.25/s (n=5668)
 file_tail: 12 wallclock secs (10.60 usr +  0.14 sys = 10.74 CPU) @ 33
+3.71/s (n=3584)
   grinder: 10 wallclock secs (10.49 usr +  0.07 sys = 10.56 CPU) @ 26
+.23/s (n=277)
     lastn: 12 wallclock secs ( 7.79 usr +  2.63 sys = 10.42 CPU) @ 26
+.97/s (n=281)
lastn_getc: 11 wallclock secs ( 8.83 usr +  1.46 sys = 10.29 CPU) @ 28
+.38/s (n=292)
  tie_file: 11 wallclock secs (10.15 usr +  0.12 sys = 10.27 CPU) @  3
+.89/s (n=40)
[download]

Well, it's good to know, at least.

Update: Heh -- I started doing this test a'fore broquaint posted; great minds think alike, eh?

Update 2: On a whim, I decided to test:

sub backticks { split /$/m, `tail -$limit $file`; }

..as well. Even given the overhead of the shell, it's still darn fast:

[chmrr@supox chmrr]$ perl -w tailbm.pl 500 100 /var/log/messages
Benchmark: timing 500 iterations of backticks, f_rb_obj, f_rb_obj_u, f
+_rb_tie, f_rb_tie_u, file_tail, grinder, lastn, lastn_getc, tie_file.
+..
 backticks:  1 wallclock secs ( 0.43 usr  0.16 sys +  0.61 cusr  0.30 
+csys =  1.50 CPU) @ 847.46/s (n=500)
  f_rb_obj:  1 wallclock secs ( 0.71 usr +  0.04 sys =  0.75 CPU) @ 66
+6.67/s (n=500)
f_rb_obj_u:  1 wallclock secs ( 0.77 usr +  0.00 sys =  0.77 CPU) @ 64
+9.35/s (n=500)
  f_rb_tie:  1 wallclock secs ( 0.89 usr +  0.02 sys =  0.91 CPU) @ 54
+9.45/s (n=500)
f_rb_tie_u:  1 wallclock secs ( 0.91 usr +  0.02 sys =  0.93 CPU) @ 53
+7.63/s (n=500)
 file_tail:  1 wallclock secs ( 1.47 usr +  0.01 sys =  1.48 CPU) @ 33
+7.84/s (n=500)
   grinder: 19 wallclock secs (18.93 usr +  0.22 sys = 19.15 CPU) @ 26
+.11/s (n=500)
     lastn: 19 wallclock secs (14.20 usr +  4.34 sys = 18.54 CPU) @ 26
+.97/s (n=500)
lastn_getc: 20 wallclock secs (15.09 usr +  2.64 sys = 17.73 CPU) @ 28
+.20/s (n=500)
  tie_file: 143 wallclock secs (126.62 usr +  1.81 sys = 128.43 CPU) @
+  3.89/s (n=500)
[download]

perl -pe '"I lo*`+$^X$\"$]!$/"=~m%(.*)%s;$_=$1;y^`+*^e v^#$&V"+@( NO CARRIER'

In reply to Re: Performing a tail(1) in Perl (reading the last N lines of a file) by Chmrr
in thread Performing a tail(1) in Perl (reading the last N lines of a file) by grinder

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