regex - Perl iterate through a file to find and save lines separately accordingly to different given patterns -

i need iterate through log file (around 2mb) line line, compare each 5 different patterns , save give match in separate arrays according pattern match with. patterns presented in file following:

(text) pattern1 pattern2 (m lines of text) pattern3 (2 lines of text) pattern1 pattern2 (x lines of text) pattern3 (this continues ~50-100 times number of lines between pattern2 , pattern3 vary) ... pattern3 (5 lines of text) pattern4 (2 lines of text) pattern5 (text) 

i aware lot of similar questions have been asked , answered, however, not understand code in answers. plan is:

1. read each line, check pattern1 , pattern2 until first match using 2 if statements exit loop immediately.

2. start while (my $line = <file>) loop, check pattern3, if match found, save line pattern3 , followings pattern1 , pattern2 lines (which 3rd , 4th lines pattern3)

here questions:

a. when exit while (<file>) loop before reaches end , start while ($line = <file>) loop after that, 2nd loop start reading top again or continue stopped?

b. can kind enough give sample commented implementation step 2?

c. how can make use of search pattern3 line pattern4 , pattern5since match pattern4 , pattern5 fixed distance away last match of pattern3.

d. plan more efficient using if-else statements checks 5 patterns every line (which, eg if there 30 pattern1's, total number of comparisons 6*30 + 4 + 5 + 5*number of lines no match)?

e. better/more efficient way solve problem? percentage of having line matched pattern around 1%.

i appreciate answer/suggestion/alternative provided. thanks

if know 5 patterns in advance, easy. you? or part of input file , unpredictable?

assuming know them in advance:

use strict; use warnings; use data::dumper;  $current_pattern = 'else'; $pattern_arrays = {     'pattern1' => [],     'pattern2' => [],     'pattern3' => [],     'pattern4' => [],     'pattern5' => [],     'else'     => [], };  while ( $line = <data> ) {     chomp($line); # remove trailing '\n' $line      # see if read 1 of our 5 patterns. remember     # $current_pattern, , proceed next line.     if ( $line =~ /^(pattern1|pattern2|pattern3|pattern4|pattern5)$/ ) {         $current_pattern = $line;         next; # jump "while...", i.e. proceed next line     }      # if here, have $current_pattern, 1     # of "pattern1" ... "pattern5" or "else". $current_pattern     # "else" @ beginning, when haven't found     # pattern yet (i.e. first line in case).     # push $line array belongs $current_pattern.     push @{$pattern_arrays->{$current_pattern}}, $line; }  # pretty-print arrays. $data::dumper::sortkeys = 1; # sort data::dumper output keys print data::dumper->dump( [$pattern_arrays], ['pattern_arrays'] );  __data__ (text) pattern1 pattern2 (m lines of text) pattern3 (2 lines of text) pattern1 pattern2 (x lines of text) pattern3 (this continues ~50-100 times number of lines between pattern2 , pattern3 vary) ... pattern3 (5 lines of text) pattern4 (2 lines of text) pattern5 (text) 

yields:

$pattern_arrays = {                     'else' => [                                 '(text)'                               ],                     'pattern1' => [],                     'pattern2' => [                                     '(m lines of text)',                                     '(x lines of text)'                                   ],                     'pattern3' => [                                     '(2 lines of text)',                                     '(this continues ~50-100 times number of lines between pattern2 , pattern3 vary)',                                     '...',                                     '(5 lines of text)'                                   ],                     'pattern4' => [                                     '(2 lines of text)'                                   ],                     'pattern5' => [                                     '(text)',                                     ''                                   ]                   }; 

actually, i'm not sure if asked for. of course, instead of <data> use other <file>.