Learning Perl - Perl Tutorial

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Hello,
I decided to learn some Perl and I found this tutorial by Nik Silver: http://www.comp.leeds.ac.uk/Perl/[^]. In the Control Structures exercise, I solved the first part: putting a line number before each line, but I don't know how to solve the second part: putting a 3-digit number before each line. Does anyone have any ideas?

Sincerely,
Mike

Posted 12-Jul-11 3:21am

mla154

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Uilleam · Answer 1 · 2011-07-12T03:31:00

It would be good if you would show what you have tried, but in absence of that, I think all you likely need to do is look up printf, and use a format like %03d. Assuming you have a decent Perl installation, you should be able to find out all you need at the command line with perldoc -f sprintf. Note that sprintf and printf use the same formatting codes, and if you know C at all they should be very familiar.

An alternative would be to use Perl's format facility which is quite powerful, but mostly unused in these days of HTML and so on. I have done some pretty fancy text formatting with it in the past for report generation, and if you're working in simple text it may be worth a look.

cheers!
Don

mla154 · Answer 2 · 2011-07-12T04:08:00

Here is a program that prints line numbers:

$file = 'results.log';
open(INFO, $file);
$count = 0;
while ($line = <INFO>)
{
$count++;
print "$count $line";
}
close(INFO);

According to the tutorial, to solve the second part, one only needs to change one line by inserting an extra four characters. I was wondering if someone knew how to do this.

However, Member 4749791, I do appreciate your input. I wish to investigate the printf statement.

Mike

Uilleam · Answer 3 · 2011-07-12T04:15:00

Thanks for the code. All you need to do is replace your print with this:
printf('%03d %s', $count, $line);

%03d specifies 3 characters of d format (signed integer in decimal, hence the 'd' - history sometimes gives us unlikely results) with leading zeros (but see what happens after line 999!)

%s is an unconstrained string format

I hope this helps!
Don

Learning Perl - Perl Tutorial

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