How do I get the output of an external command in Perl?

Question

I want to have output of Windows command-line program (say, powercfg -l) written into a file which is created using Perl and then read the file line by line in

Answer 1

There is no need to first save the output of the command in a file:

my $output = `powercfg -l`;

See qx// in Quote-Like Operators.

However, if you do want to first save the output in a file, then you can use:

my $output_file = 'output.txt';

system "powercfg -l > $output_file";

open my $fh, '<', $output_file 
    or die "Cannot open '$output_file' for reading: $!";

while ( my $line = <$fh> ) {
    # process lines
}

close $fh;

See perldoc -f system.