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Top Forums UNIX for Dummies Questions & Answers How to get nth line from a file usuing commands Post 302240624 by radoulov on Friday 26th of September 2008 06:50:52 AM
Old 09-26-2008
Or:

Code:
sed '789!d;q' infile

A quick test:

Code:
$ time head -813000 alert_xxx.log | tail -1
Starting control autobackup

real    0m5.457s
user    0m1.110s
sys     0m6.710s
$ time sed '813000!d;q' alert_xxx.log
Starting control autobackup

real    0m0.721s
user    0m0.470s
sys     0m0.200s

 

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File::Path::Tiny(3pm)					User Contributed Perl Documentation				     File::Path::Tiny(3pm)

NAME
File::Path::Tiny - recursive versions of mkdir() and rmdir() without as much overhead as File::Path VERSION
This document describes File::Path::Tiny version 0.3 SYNOPSIS
use File::Path::Tiny; if(!File::Path::Tiny::mk($path)) { die "Could not make path '$path': $!"; } if(!File::Path::Tiny::rm($path)) { die "Could not remove path '$path': $!"; } DESCRIPTION
The goal here is simply to provide recursive versions of mkdir() and rmdir() with as little code and overhead as possible. This module is in no way meant to derogate File::Path and is in no way an endorsement to go out and replace all use of File::Path with File::Path::Tiny. File::Path is very good at what it does but there's simply a lot happening that we can do without much of the time. Here are some things File::Path has/does that this module attempts to do without: o multiple interfaces Backwards compatibility brings in a lot of code and logic that we don't need from here on out. o chdir's It does a ton of chdir's which could leave you somewhere you're not planning on being and requires much more overhead to do. o can croak not allowing you to detect and handle failure Just let me handle errors how I want. Don't make my entire app die or have to wrap it in an eval o A well intentioned output system Just let me do the output how I want. (Nothing, As HTML, print to a filehandle, etc...) o A well intentioned and experimental (IE subject to change) error handling system. Just keep it simple and detect failure via a boolean check and do what I want with the error. See "How can I make/remove multiple paths?" o According to its POD, removing a tree is apparently not safe unless you tell it to be with the 'safe' or 'keep_root' attributes. Seems like that should just happen, I don't want to worry about accidentally removing / when I pass it /tmp INTERFACE
Nothing in exported or exportable, that helps keep it '::Tiny'. File::Path::Tiny::mk() Takes a single path (like mkdir()) to recursively create and, optionally, a mask (like mkdir()) for all subsequent mkdir() calls. Mask defaults to 0700 (also like mkdir()) Returns false if it could not be made, true otherwise (returns '2' if it is -d already) It is recursive in the sense that given foo/bar/baz as the path to create all 3 will be created if necessary. File::Path::Tiny::rm() Takes a single path (like rmdir()) to recursively empty and remove. Returns false if it could not be emptied or removed, true otherwise. (returns '2' if it is !-d already) It is recursive in the sense that given /foo/bar/baz as the path to remove it will recursively empty 'baz' and then remove it from /foo/bar. Its parents, /, /foo, and /foo/bar are *not* touched. File::Path::Tiny::empty_dir() Takes a single path to recursively empty but not remove. Returns false when there is a problem. DIAGNOSTICS
Throws no warnings or errors of its own If the functions ever return false, $! will have been set either explicitly or by the mkdir(), rmdir(), unlink(), or opendir() that ultimately returned false. MISC
How can I make/remove multiple paths? For simplicity sake && ::Tiny status this module must be very very very simple. That said it is also very simple to do muliple paths: for my $path (@paths) { File::Path::Tiny::::mk($path) or _my_handle_failed_mk($path, $!); } for my $path (@paths) { File::Path::Tiny::::rm($path) or _my_handle_failed_rm($path, $!); } That also lets you keep going or short circuit it or handle errors however you like: PATH: for my $path qw(foo/bar bar/rat) { if (!File::Path::Tiny::mk($path)) { print "problem unlinking '$path': $! "; last PATH; } else { print "No error encountered with '$path' " } } About the '::Tiny' status See Acme::Tiny for information on the ::Tiny suffix. #3 is almost there (< 1/5th +/-), a bit more trimming and I think we'll have it! #8 is N/A since part of the "sub set" is to do single paths like their non-recursive core counterparts and there are so many ways to invoke it with different consequences [ -- RSS Memory -- ] Baseline perl 1168 File::Path 1808 (+640) File::Path::Tiny 1288 (+120) Even though "time" isn't really a ::Tiny factor, it does improve loading a bit: [ -- time -- ] Baseline perl real 0m0.007s user 0m0.002s sys 0m0.004s File::Path real 0m0.017s user 0m0.011s sys 0m0.005s File::Path::Tiny real 0m0.007s user 0m0.003s sys 0m0.004s As time allows and more tests are added I'll try to include more comprehensive benchmark results. How do I make sure the path is safe to create or remove? Of course the answer depends on what you mean by "safe". This module makes no assumptions on interpreting the "safeness" of a path, just like mkdir() and rmdir(). Also like mkdir() and rmdir() typically you'll find that filesystem permissions are a pretty reliable tool (of course if the code will be run as root you would want to setuid first...) You might use Cwd::abs_path() to sanitize a path before sending it to be made or removed. Even after that it might not be "safe" so you'll need to discern what your particular definition of "safe" is and take appropriate action. DEPENDENCIES
File::Spec of course but its only loaded if needed INCOMPATIBILITIES
None reported. BUGS AND LIMITATIONS
No bugs have been reported. Please report any bugs or feature requests to "bug-file-path-tiny@rt.cpan.org", or through the web interface at <http://rt.cpan.org>. AUTHOR
Daniel Muey "<http://drmuey.com/cpan_contact.pl>" LICENCE AND COPYRIGHT
Copyright (c) 2008, Daniel Muey "<http://drmuey.com/cpan_contact.pl>". All rights reserved. This module is free software; you can redistribute it and/or modify it under the same terms as Perl itself. See perlartistic. DISCLAIMER OF WARRANTY
BECAUSE THIS SOFTWARE IS LICENSED FREE OF CHARGE, THERE IS NO WARRANTY FOR THE SOFTWARE, TO THE EXTENT PERMITTED BY APPLICABLE LAW. EXCEPT WHEN OTHERWISE STATED IN WRITING THE COPYRIGHT HOLDERS AND/OR OTHER PARTIES PROVIDE THE SOFTWARE "AS IS" WITHOUT WARRANTY OF ANY KIND, EITHER EXPRESSED OR IMPLIED, INCLUDING, BUT NOT LIMITED TO, THE IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR PURPOSE. THE ENTIRE RISK AS TO THE QUALITY AND PERFORMANCE OF THE SOFTWARE IS WITH YOU. SHOULD THE SOFTWARE PROVE DEFECTIVE, YOU ASSUME THE COST OF ALL NECESSARY SERVICING, REPAIR, OR CORRECTION. IN NO EVENT UNLESS REQUIRED BY APPLICABLE LAW OR AGREED TO IN WRITING WILL ANY COPYRIGHT HOLDER, OR ANY OTHER PARTY WHO MAY MODIFY AND/OR REDISTRIBUTE THE SOFTWARE AS PERMITTED BY THE ABOVE LICENCE, BE LIABLE TO YOU FOR DAMAGES, INCLUDING ANY GENERAL, SPECIAL, INCIDENTAL, OR CONSEQUENTIAL DAMAGES ARISING OUT OF THE USE OR INABILITY TO USE THE SOFTWARE (INCLUDING BUT NOT LIMITED TO LOSS OF DATA OR DATA BEING RENDERED INACCURATE OR LOSSES SUSTAINED BY YOU OR THIRD PARTIES OR A FAILURE OF THE SOFTWARE TO OPERATE WITH ANY OTHER SOFTWARE), EVEN IF SUCH HOLDER OR OTHER PARTY HAS BEEN ADVISED OF THE POSSIBILITY OF SUCH DAMAGES. perl v5.14.2 2012-04-04 File::Path::Tiny(3pm)
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