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Perl: testing for blank lines

i'm trying to find blank lines in a text file
this is the code

Code:

use strict;

use warnings;



open (FILE, '<', 'file1.txt') or die "$!";



while (<FILE>)

{

        if ($_ == "")

        {

                print "it's blank\n";

        }

        elsif ($_ != "")

        {

                print "it's NOT blank\n";

        }

}

this is file1.txt

Code:

it seems to work ok, but i keep getting warnings

i'm pretty sure that
if ($_ == "")
is the wrong way to test for an empty string, what should i be doing instead?

edit: i'm kinda confused also, because i think blank lines are actually nothing, followed by the new like character, but i still get the "it's blank" message

Hi,

Try this:

Code:

#!/bin/perl

use strict;

use warnings;



open (FILE, '<', 'file1.txt') or die "$!";



while (<FILE>)

{

  if ($_ =~ /^$/)

  {

    print "it's blank\n";

  }

  else

  {

    print "it's NOT blank\n";  

  }

}

This: $_ =~ /^$/ can also be written as /^$/. Perl assumes a check against $_ in the last case.

Hope this helps.

thanks for that, i was pretty sure that i was checking for empty lines in the wrong way

You might want to try:

Code:

/^\s*$/

if your "blank" lines may contain spaces or tabs.

Brian

You used the == to test for an empty string, but this is the numerical equality test. You should use eq for strings. Also $_ will not equal "" for a blank line - it will equal "\n". If you want to get rid of the newline character before testing, use chomp first.

Code:

while (<FILE>) {

    chomp;

    if ( $_ eq "" ) { print "empty line at input line number $.\n"; }

}

A regular expression might also be useful, matching not only completely empty lines but those with whitespace. You don't have to chomp if you're using regular expressions - they're smart enough to handle them. Personally I like to chomp anyway - I find that more often than not I don't want the \n on the end of the line, plus I like the word "chomp":

Code:

while (<FILE>) {

    chomp;  # just because!

    if ( /^\s*$/ ) { 

        print "empty line, or line with only whitespace at line $.\n"; 

    }

}

P.S. don't forget to close your FILE handle.
P.P.S. when calling open, you don't need to separate the <. You can call it like this: open(FILE, "<myfilename") || die ...;