Perl – What’s the differences between system and backticks and pipes in Perl

backticksperlpipesystem

Perl supports three ways (that I know of) of running external programs:

system:

   system PROGRAM LIST

as in:

system "abc";

backticks as in:

`abc`;

running it through a pipe as in:

open ABC, "abc|";

What are the differences between them? Here's what I know:

Also backticks redirects the executed program's STDOUT to a variable, and system sends it to your main program's STDOUT.

I don't know of any default way to do this, but you can define a subroutine to do it for you:

sub execute {
    my $cmd = shift;
    print "$cmd\n";
    system($cmd);
}

my $cmd = $ARGV[0];
execute($cmd);

And then see it in action:

pbook:~/foo rudd$ perl foo.pl ls
ls
file1   file2   foo.pl

There are no universal standards, but there are reasons to prefer one or another. My preferred form is this:

open( my $input_fh, "<", $input_file ) || die "Can't open $input_file: $!";

The reasons are:

You report errors immediately. (Replace "die" with "warn" if that's what you want.)
Your filehandle is now reference-counted, so once you're not using it it will be automatically closed. If you use the global name INPUT_FILEHANDLE, then you have to close the file manually or it will stay open until the program exits.
The read-mode indicator "<" is separated from the $input_file, increasing readability.

The following is great if the file is small and you know you want all lines:

my @lines = <$input_fh>;

You can even do this, if you need to process all lines as a single string:

my $text = join('', <$input_fh>);

For long files you will want to iterate over lines with while, or use read.