in reply to Re: Parsing a file line by line until a certain indice in array
in thread Parsing a file line by line until a certain indice in array

Hello Liverpole,

Thank you very much for your help and insight, I am better understanding how to think when programming in Perl as well as the structure.

The file I am parsing, contains each volume on a separate line, but then at the bottom it repeats every line but without \n, which I believe is a side-effect of parsing all volumes at once with the script that I am using.

I wanted to make the pars0r subroutine skip printing the '$vol_to_parse got got' to STDOUT for every instance of john after the first.

Is the proper way in Perl to make another nested if statement inside the existing if statement under the pars0r subroutine? I was thinking to declare a counter to increment/count how many times it showed up and only print the first instance. Is there an easier way to skip every instance of john after the first instance?

Something like:

sub pars0r{  
    foreach my $volume (@raw_data) {
        if ($volume =~ /$vol_to_parse/) {
           my $counter++; 
           if($counter <=1){
           print "$vol_to_parse got got \n"; 
          }
         elsif (
          $counter > 1 ) {
           next; # or break; ?     
                } 
       }
    }
}

[download]

Am I approaching the logic in this the wrong way?

This is my code so far, but it prints out the line 'john got got' 6 times as opposed to one, where did I go wrong?

#!/usr/bin/perl


#Libraries
use strict;
use warnings;
use Getopt::Long;

#Globals and default arguments

my $vol_to_parse = "john";
my $file_to_parse = "file1.txt";
my @raw_data;

my $counter=0;
#Main Program
process_args();
open_sesame();
pars0r();

#Subroutines
sub process_args{
    GetOptions (
        'v=s' => \$vol_to_parse,
        'h=s' => \$file_to_parse,
    ) or die "syntax:   $0 -v <volume> -h <file>\n";
}

sub open_sesame{
    open(DAT, "<", $file_to_parse) || die "Could not open file! ($!)\n
+ +";
    chomp(@raw_data = <DAT>);
    close(DAT);
}

sub pars0r{
    foreach my $volume (@raw_data) {
        if ($volume =~ /$vol_to_parse/){
           $counter++;
       }
           if ($counter >=1){
            print "$vol_to_parse got got \n";
        }
        elsif( $counter > 1){
            next;
        }
            
        }
    }

[download]

Output is: 

john got got 
john got got 
john got got 
john got got 
john got got 
john got got

[download]

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Re^3: Parsing a file line by line until a certain indice in array
by liverpole (Monsignor) on Sep 05, 2009 at 21:52 UTC
    Hi sluggo,

    Your first example of pars0r immediately above has a subtle bug in it -- you have my $counter++ instead of $counter++.   This has the effect of creating a new instance of $counter, which is why you'll be printing "$vol_to_parse got got\n" every time you get a match: 

    sub pars0r{
    foreach my $volume (@raw_data) {
        if ($volume =~ /$vol_to_parse/) {
            my $counter++;            # Create new $counter, set it to
+ 1
            if($counter <= 1){        # This will always be true
                print "$vol_to_parse got got \n"; 
            }
            elsif ($counter > 1 ) {   # Block will never be executed
                next; # or break; ?
            } 
        }
    }
}

    [download]

    If you take out the $my it should function correctly.

    Your second example of pars0r immediately above has a different bug; even if you change the if ($counter >= 1) to if ($counter <= 1) as I think you meant, once you've found the first match, and until you find a second one, you will always print "$vol_to_parse got got\n": 

    sub pars0r{
    foreach my $volume (@raw_data) {
        if ($volume =~ /$vol_to_parse/){
            $counter++;            # Set counter to one the first time
        }
        if ($counter <= 1){        # Changed ">= 1" to "<= 1"
            # This block executes after the first match, and up to
            # the next non-match, which is NOT what you want!
            ##
            print "$vol_to_parse got got \n";
        }
        elsif( $counter > 1){
            next;
        }
    }
}

    [download]

    Why not just do something like this: 

    sub pars0r{
    my $b_got_match = 0;        # Initialize boolean to FALSE
    foreach my $volume (@raw_data) {
        if ($volume =~ /$vol_to_parse/){
            if (!$b_got_match) {
                # Only print the match once, as $b_got_match gets
                # set once we print it, and then this conditional
                # will never again get executed.
                ##
                print "$vol_to_parse got got\n";
                $b_got_match = 1;
            }
            # We can still track the total number of matches
            ++$counter;
        }
    }
}

    [download]
    s''(q.S:$/9=(T1';s;(..)(..);$..=substr+crypt($1,$2),2,3;eg;print$..$/
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