Detect empty line (contain only space) in perl - regex

Question

my program read a file, and i don't want to treat empty line
while (<FICC>) {
my $ligne=$_;
if ($ligne =~ /^\s*$/){}else{
print " $ligne\n";}
but this code also print empty line
the file that i test with contain:
Ms. Ruth Dreifuss Dreifuss Federal Councillor Federal ruth
     
sir christopher warren US Secretary of state secretary of state
     
external economic case federal economic affair conference the Federal Office case
     
US bill clinton bill clinton Mr. Bush
     
Nestle food cs holding swiss Swiss Performance Index Performance

Answer 1

I think it is because of using the \n within your code. Just remove that \n from your code and it should be fine.
Usually people do chomp after reading a line from a file to remove the end of line character.

Answer 2

An easier way to write that is probably to invert the logic and only print lines that contain non-whitespace characters.
while (<FICC>) {
my $ligne = $_;
if ($ligne =~ /\S/) {
print " $ligne"; # No need for linefeed here as $ligne already has one
}
}
Update: Demo using your sample data:
#!/usr/bin/perl
use strict;
use warnings;
while (<DATA>) {
my $ligne = $_;
if ($ligne =~ /\S/) {
print " $ligne";
}
}
__END__
Ms. Ruth Dreifuss Dreifuss Federal Councillor Federal ruth
sir christopher warren US Secretary of state secretary of state
external economic case federal economic affair conference the Federal Office case
US bill clinton bill clinton Mr. Bush
Nestle food cs holding swiss Swiss Performance Index Performance
Output:
Ms. Ruth Dreifuss Dreifuss Federal Councillor Federal ruth
sir christopher warren US Secretary of state secretary of state
external economic case federal economic affair conference the Federal Office case
US bill clinton bill clinton Mr. Bush
Nestle food cs holding swiss Swiss Performance Index Performance
Which seems correct to me.

Answer 3

The reason is also that you're adding a new line, to the end of your string which already has a newline in it "$ligne\n", so use chomp as below
I think the nicer way of doing this is with next (skip to next loop iteration) as it removes some brackets from your code:
while (<FICC>) {
my $ligne=chomp $_;
next if $ligne =~ /^\s*$/;
print " $ligne\n";
}