• Read perlintro
• Write some code.
• Post back here if you have specific questions about your code.

I was thinking something like this #!/usr/bin/perl -w use strict; my $infile = $ARGV[0]; open (IN, $infile); my $threshold = 1e-50; while (my $line = <IN>) { my @linearray = split("\t", $line); if($linearray2 <$threshold) { print "$linearray[0]\n"; } } Would that work or is there some smarter and better way?

Hello SandraA, and welcome to the Monastery!

Please enclose your code in <code> ... </code> tags, that will make it much easier to read (and $linearray[2] will display correctly).

Your approach is essentially the same as that given by muba, and it should work fine, except:

1. You are printing the line only if the third field is less than the threshold, but your original specification was: to print the first one if the third one was larger than my threshold (underlining added). See perlop#Relational-Operators.
2. You are splitting on "\t", which is fine as long as the data fields are always separated by single tabs. But splitting on whitespace, using /\s+/ or the equivalent ' ', is probably safer. See split.

...is there some smarter and better way?

Well, if you’re into one-liners, then (assuming your data is in, say, a file called “data.txt” in the current directory) you can do this:

>perl -anE "BEGIN { $threshold = shift; } say $F[0] if $F[2] > $thresh
+old;" 1e-50 data.txt
[download]

The -a, -n, and -E switches are explained in perlrun. But code stored in a file is, IMO, easier to debug, reuse, and maintain.

Hope that helps,

Athanasius <°(((>< contra mundum

Iustus alius egestas vitae, eros Piratica,

Sounds like a dang fine approach to me.

use strict;
use warnings;
use feature 'say';
my $minimum = 100;                      # The threshold.
while(<DATA>) {                         # Read it
    my ($str, undef, $nr) = split / /;  # Split it
    say $str if $nr >= $minimum;        # Say it
}
__DATA__
Too low 1
Also nope 2
Just fine 100
Not there 3
Hidden hideaway 4
Another one 101
Hiding quierly 5
Also no 6
Perl rocks! 102
Again no 7
Nope nopenope 8
Hacker hackityhack 103
Cracker crackitycrack 9
Hater hatitiyhate 10
[download]

Just
Another
Perl
Hacker
[download]

It even works, too!