How can I extract a line or row?

Question

How can I extract the whole line in a row, for example, row 3. These data are saved in my text editor in linux. Here's my data:

1,julz,kath,shiela,angel
2,may,ann,janice,aika
3,christal,justine,kim
4,kris,allan,jc,mine

I want output like:

3,christal,justine,kim

Answer 1

You can assign the diamond operator on your filehandle to a list, each element will be a line or row.

open $fh, "myfile.txt";
my @lines = <$fh>;

EDIT: This solution grabs all the lines so that you can access any one you want, e.g. row 3 would be $lines[2] ... If you really only want one specific line, that'd be a different solution, like the other answerers'.

Answer 2

$ perl -ne'print if $. == 3' your_file.txt

Below is a script version of @ysth's answer:

$ perl -mTie::File -e'tie @lines, q(Tie::File), q(your_file.txt); 
> print $lines[2]'

Answer 3

The following snippet reads in the first three lines, prints only the third then exits to ensure that no unnecessary processing takes place.

Without the exit, the script would continue to process the input file despite you knowing that you have no use for it.

perl -ne 'if ($. == 3) {print;exit}' infile.txt

As perlvar points out, $. is the current line number for the last file handle accessed.

Answer 4

If it's always the third line:

perl -ne 'print if 3..3' <infile >outfile

If it's always the one that has a numeric value of "3" as the first column:

perl -F, -nae 'print if $F[0] == 3' <infile >outfile # thanks for the comment doh!

Since you didn't say how you were identifying that line, I am providing alternatives.

Answer 5

Um, the -n answers are assuming the question is "what is a script that...". In which case, perl isn't even the best answer. But I don't read that into the question.

In general, if the lines are not of fixed length, you have to read through a file line by line until you get to the line you want. Tie::File automates this process for you (though since the code it would replace is so trivial, I rarely bother with it, myself).

use Tie::File;
use Fcntl "O_RDONLY";
tie my @line, "Tie::File", "yourfilename", mode => O_RDONLY
    or die "Couldn't open file: $!";
print "The third line is ", $line[2];

Answer 6

For a more general solution:

open my $fh, '<', 'infile.txt';
while (my $line = <$fh>) {
  print $line if i_want_this_line($line);
}

where i_want_this_line implements the criteria defining which line(s) you want.