Perl read line by line

Question

I have a simple Perl script to read a file line by line. Code is below. I want to display two lines and break the loop. But it doesn't work. Where is the bug?

$file='SnPmaster.txt'; open(INFO, $file) or die("Could not open  file.");  $count = 0;  foreach $line (<INFO>)  {        print $line;         if ($++counter == 2){       last;     } } close(INFO); 

Answer 1

If you had use strict turned on, you would have found out that $++foo doesn't make any sense.

Here's how to do it:

use strict; use warnings;  my $file = 'SnPmaster.txt'; open my $info, $file or die "Could not open $file: $!";  while( my $line = <$info>)  {        print $line;         last if $. == 2; }  close $info; 

This takes advantage of the special variable $. which keeps track of the line number in the current file. (See perlvar)

If you want to use a counter instead, use

my $count = 0; while( my $line = <$info>)  {        print $line;         last if ++$count == 2; } 

Answer 2

With these types of complex programs, it's better to let Perl generate the Perl code for you:

$ perl -MO=Deparse -pe'exit if $.>2' 

Which will gladly tell you the answer,

LINE: while (defined($_ = <ARGV>)) {     exit if $. > 2; } continue {     die "-p destination: $!\n" unless print $_; } 

Alternatively, you can simply run it as such from the command line,

$ perl -pe'exit if$.>2' file.txt