Read multiple columns in perl using while loop

Question

I am stuck in a problem in Perl.

I want to read multiple columns in 1 line using while loop.

I know I can achieve this using shell script like below

cat file.txt|while read field1 field2 field3 field4
do
statement1
statement2
done

The same thing I want in Perl but don't understand how to get this.

Please help me.

Thanks in advance, Sumana

Yes, there might be many fields in file but I want to extract only n number of fields like shown above and then I will use these variables below. I know array is alternative but I wanted to check if there is any easier method available like shell provides here. — sumana
– sumana, Commented Dec 30, 2012 at 4:50
@Sumana, that doesn't extract n fields. What happens is all fields after the 4th get slurped into your "field4" variable. Maruice's answer behaves exactly the same. To discard the remaining, you need an additional _ in bash or undef in the perl version. — jordanm
– jordanm, Commented Dec 30, 2012 at 6:14
@jordanm - good point. I was working off the assumption of three fields. Feel free to edit the script to reflect this reality if you want, or I can later on. — Maurice Reeves
– Maurice Reeves, Commented Dec 30, 2012 at 6:20

jordanm · Accepted Answer · 2012-12-30 06:11:46Z

2

In a loop, you can do this:

#!/usr/bin/perl -w
use strict;

my $file = "MYFILE";
open (my $fh, '<', $file) or die "Can't open $file for read: $!";
my @lines;
while (<$fh>) {
    my ($field1, $field2, $field3) = split;
}
close $fh or die "Cannot close $file: $!";

In the loop, Perl will assign $_ the next line of the file, and with no args, split will split that variable on white space.

edited Dec 30, 2012 at 6:11

jordanm

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answered Dec 30, 2012 at 4:53

Maurice Reeves

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2 Comments

sumana Over a year ago

Yes. It solved my purpose. Thank you very much Maurice for your kind help.

Maurice Reeves Over a year ago

My pleasure! Best of luck, and when you have a chance, if you haven't already, please mark my answer as accepted. Cheers!

Vijay · Accepted Answer · 2012-12-30 07:25:01Z

2

use

perl -F -ane '....' your file

-F flag will store each field in an array @F.so u can use $F[0] for the first field. for example:

perl -F -ane 'print $F[0]' your file

will print the first field of every line

if you are concerned about performance:

perl -lne "my($f,$s,$t)=split;print 'first='.$f.' second='.$s.' third='.$t" your_file

for a big example :also check this

edited Dec 30, 2012 at 7:25

answered Dec 30, 2012 at 4:47

Vijay

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1 Comment

sumana Over a year ago

I know array can solve this purpose but that's a bit lengthy and it uses memory also to assign many unwanted values so I wanted to check if Perl also provide any easier method like shell as in my example.

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