Conditionally print elements in a text file - perl

Question

I have a text file of the following format:
1 4730 1031782 init
4 0 6 events
2190 450 0 top
21413 5928 1 sshd
22355 1970 2009 find
I want to print rows of this file only if the second column of data meets the requirement >= 2000 - how can I do this?
Currently I am reading the file and printing it like so:
sub read_file{
my $data_failed = 1;
my $file = 'task_file';
if(open (my $file, "task_file" || die "$!\n")){
my #COLUMNS = qw( memory cpu program );
my %sort_strings = ( program => sub { $a cmp $b } );
my (%process_details, %sort);
while (<$file>) {
$data_failed = 0;
my ($process_id, $memory_size, $cpu_time, $program_name) = split;
$process_details{$process_id} = { memory => $memory_size,
cpu => $cpu_time,
program => $program_name };
undef $sort{memory}{$memory_size}{$process_id};
undef $sort{cpu}{$cpu_time}{$process_id};
undef $sort{program}{$program_name}{$process_id};
}
if($option_a == 1){
if (-z $file){print "No tasks found\n";}
for my $column ($COLUMNS[2]) {
my $cmp = $sort_strings{$column} || sub { $a <=> $b };
for my $value (sort $cmp keys %{ $sort{$column} }
) {
my #pids = keys %{ $sort{$column}{$value} };
say join ' ', $_, #{ $process_details{$_} }{#COLUMNS}
for #pids;
}
}
}
} else { print "No tasks found\n"}
}
The if($option_a == 1) bit is just reading values from another function that parses command line options.

Answer 1

my ($process_id, $memory_size, $cpu_time, $program_name) = split;
At this point, you can complete the loop, or you can continue to the next line. Just add the line:
next if $memory_size < 2000;
right after the split, and you'll eliminate all the records in memory that fail to meet your requirements.

Answer 2

Filtering a list is easily done with grep:
#!/usr/bin/perl
use strict;
use feature qw{ say };
use warnings;
my #COLUMNS = qw( memory cpu program );
my (%process_details, %sort);
while (<DATA>) {
my ($process_id, $memory_size, $cpu_time, $program_name) = split;
$process_details{$process_id} = { memory => $memory_size,
cpu => $cpu_time,
program => $program_name };
undef $sort{memory}{$memory_size}{$process_id};
undef $sort{cpu}{$cpu_time}{$process_id};
undef $sort{program}{$program_name}{$process_id};
}
for my $value (sort { $a cmp $b } keys %{ $sort{program} }) {
my #pids = grep $process_details{$_}{memory} > 2000,
keys %{ $sort{program}{$value} };
say join ' ', $_, #{ $process_details{$_} }{#COLUMNS}
for #pids;
}
__DATA__
...

Answer 3

Something like this perhaps:
#!/usr/bin/perl
use strict;
use warnings;
while (<DATA>) {
print if (split)[1] > 2000;
}
__DATA__
1 4730 1031782 init
4 0 6 events
2190 450 0 top
21413 5928 1 sshd
22355 1970 2009 find
With no arguments, split() splits $_ on whitespace (which is what we want). We can then use a list slice to look at the second element of that and print the line if that value is greater than 2000.