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Full Discussion: Want to remove all lines but not latest 50 lines from a file
Top Forums UNIX for Dummies Questions & Answers Want to remove all lines but not latest 50 lines from a file Post 302868247 by drl on Saturday 26th of October 2013 05:34:08 PM
Old 10-26-2013
Hi.

Both of the solutions, shell variable and "dd move" are about the same as far as system resources go. I used alister's amended solution; his first failed (the one that went out with an email notification).

For a file of 14,754,910 lines, about 1 GB, the times for the shell solution keeping the last 50,000 lines were:
Code:
real	0m36.738s
user	0m1.624s
sys	0m8.321s

and for the clever "dd move" solution:
Code:
real	0m44.048s
user	0m1.408s
sys	0m8.725s

There were 2 wc executions for verification in both runs. Leaving those out:
Code:
real	0m29.443s
user	0m0.560s
sys	0m7.012s

and
Code:
real	0m30.536s
user	0m0.220s
sys	0m6.460s

The results actually surprised me -- I thought the shell would be slower. I saw paging being used a few times, slightly more often with the dd. The shell was run first, so cache advantage, if any, went to dd ... cheers, drl

This system:
Code:
 OS: Debian 5.0.8 lenny
 Kernel: x86_64 Linux 2.6.26-2-amd64
 Uptime: 59d 21h 58m
 CPU: AMD Athlon 64 3000+ @ 1.802GHz
 GPU: NVidia GeForce FX 5200
 RAM: 1170MB / 3024MB

Last edited by drl; 10-26-2013 at 06:39 PM.. Reason: Typo.
This User Gave Thanks to drl For This Post:
alister
 

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LEARN ABOUT MOJAVE

locale::codes::langvar

Locale::Codes::LangVar(3pm)				 Perl Programmers Reference Guide			       Locale::Codes::LangVar(3pm)

NAME

       Locale::Codes::LangVar - standard codes for language variation identification

SYNOPSIS

	  use Locale::Codes::LangVar;

	  $lvar = code2langvar('acm');		       # $lvar gets 'Mesopotamian Arabic'
	  $code = langvar2code('Mesopotamian Arabic'); # $code gets 'acm'

	  @codes   = all_langvar_codes();
	  @names   = all_langvar_names();

DESCRIPTION

       The "Locale::Codes::LangVar" module provides access to standard codes used for identifying language variations, such as those as defined in
       the IANA language registry.

       Most of the routines take an optional additional argument which specifies the code set to use. If not specified, the default IANA language
       registry codes will be used.

SUPPORTED CODE SETS

       There are several different code sets you can use for identifying language variations. A code set may be specified using either a name, or
       a constant that is automatically exported by this module.

       For example, the two are equivalent:

	  $lvar = code2langvar('en','alpha-2');
	  $lvar = code2langvar('en',LOCALE_CODE_ALPHA_2);

       The codesets currently supported are:

       alpha
	   This is the set of alphanumeric codes from the IANA language registry, such as 'arevela' for Eastern Armenian.

	   This code set is identified with the symbol "LOCALE_LANGVAR_ALPHA".

	   This is the default code set.

ROUTINES

       code2langvar ( CODE [,CODESET] )
       langvar2code ( NAME [,CODESET] )
       langvar_code2code ( CODE ,CODESET ,CODESET2 )
       all_langvar_codes ( [CODESET] )
       all_langvar_names ( [CODESET] )
       Locale::Codes::LangVar::rename_langvar  ( CODE ,NEW_NAME [,CODESET] )
       Locale::Codes::LangVar::add_langvar  ( CODE ,NAME [,CODESET] )
       Locale::Codes::LangVar::delete_langvar  ( CODE [,CODESET] )
       Locale::Codes::LangVar::add_langvar_alias  ( NAME ,NEW_NAME )
       Locale::Codes::LangVar::delete_langvar_alias  ( NAME )
       Locale::Codes::LangVar::rename_langvar_code  ( CODE ,NEW_CODE [,CODESET] )
       Locale::Codes::LangVar::add_langvar_code_alias  ( CODE ,NEW_CODE [,CODESET] )
       Locale::Codes::LangVar::delete_langvar_code_alias  ( CODE [,CODESET] )
	   These routines are all documented in the Locale::Codes::API man page.

SEE ALSO

       Locale::Codes
	   The Locale-Codes distribution.

       Locale::Codes::API
	   The list of functions supported by this module.

       http://www.iana.org/assignments/language-subtag-registry
	   The IANA language subtag registry.

AUTHOR

       See Locale::Codes for full author history.

       Currently maintained by Sullivan Beck (sbeck@cpan.org).

COPYRIGHT

	  Copyright (c) 2011-2013 Sullivan Beck

       This module is free software; you can redistribute it and/or modify it under the same terms as Perl itself.

perl v5.18.2							    2014-01-06					       Locale::Codes::LangVar(3pm)
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