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Top Forums Shell Programming and Scripting Help with perl code understanding Post 302858851 by learnbash on Tuesday 1st of October 2013 01:57:52 PM
Old 10-01-2013
Help with perl code understanding

Hi,

I need to understand below perl code, can some one advise me.

Code:
perl -MDate::Parse -e'BEGIN{$main::now=time;$main::old=(time-60*30)}' -nE'if(/^(\w+\s+\d+\s+\d+:\d+:\d+)/) {$t=str2time $1; $t > $old && $t < $now && print}'

 

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YAPP(1) 						User Contributed Perl Documentation						   YAPP(1)

NAME
yapp - A perl frontend to the Parse::Yapp module SYNOPSYS
yapp [options] grammar[.yp] yapp -V yapp -h DESCRIPTION
yapp is a frontend to the Parse::Yapp module, which lets you compile Parse::Yapp grammar input files into Perl LALR(1) OO parser modules. OPTIONS
Options, as of today, are all optionals :-) -v Creates a file grammar.output describing your parser. It will show you a summary of conflicts, rules, the DFA (Deterministic Finite Automaton) states and overall usage of the parser. -s Create a standalone module in which the driver is included. Note that if you have more than one parser module called from a program, to have it standalone, you need this option only for one of your parser module. -n Disable source file line numbering embedded in your parser module. I don't know why one should need it, but it's there. -m module Gives your parser module the package name (or name space or module name or class name or whatever-you-call-it) of module. It defaults to grammar -o outfile The compiled output file will be named outfile for your parser module. It defaults to grammar.pm or, if you specified the option -m A::Module::Name (see below), to Name.pm. -t filename The -t filename option allows you to specify a file which should be used as template for generating the parser output. The default is to use the internal template defined in Parse::Yapp::Output.pm. For how to write your own template and which substitutions are available, have a look to the module Parse::Yapp::Output.pm : it should be obvious. -b shebang If you work on systems that understand so called shebangs, and your generated parser is directly an executable script, you can specifie one with the -b option, ie: yapp -b '/usr/local/bin/perl -w' -o myscript.pl myscript.yp This will output a file called myscript.pl whose very first line is: #!/usr/local/bin/perl -w The argument is mandatory, but if you specify an empty string, the value of $Config{perlpath} will be used instead. grammar The input grammar file. If no suffix is given, and the file does not exists, an attempt to open the file with a suffix of .yp is tried before exiting. -V Display current version of Parse::Yapp and gracefully exits. -h Display the usage screen. BUGS
None known now :-) AUTHOR
Francois Desarmenien <francois@fdesar.net> COPYRIGHT
(c) Copyright 1998-1999 Francois Desarmenien, all rights reserved. See Parse::Yapp(3) for legal use and distribution rights SEE ALSO
Parse::Yapp(3) Perl(1) yacc(1) bison(1) perl v5.16.3 2001-02-11 YAPP(1)
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