PERL:how to find a blank line in a file--regular expression
 

soursefile:
this is the first line
this is the second line

this is the third line
this is the fourth line

I want to tell wether there is a blank line and delete it.
so I write the code as follows:
#!/usr/bin/perl
$filename="d:\\text";
open($in,$filename)||die"can not open source file";
open(OUT,">>d:\\text01")||die"can not create file";
while($str=<$in>)
{
if($str!=~/\s/){print "yes";print OUT $str;}
}
close($in);
close(OUT);

but it didn't work.Do you have any ideas what to do?

if($str!=~/\s/){print "yes";print OUT $str;}
should be
unless($str =~ /^\s*$/){print "yes";print OUT $str;}

That'll match completely empty lines (^$) as well as line consisting of only whitespace.

thanks,it did work.but I am still confused about that,what shoud I do if I want to use the if sentense,since if and unless sentense can be represented for each other?

Here's how I ignore/skip empty file recs and those starting with a comment in a cfg file