system("linux_command") vs. Perl library functions

Question

In Perl, one can either use a Perl builtin or use system() which calls a shell command to achieve the some goal. The problem is, for me as a Perl beginner, it's sometimes difficult to find the Perl equivalent to a Linux command.
Take this one for example:

cat file1 file2 | sort -u > file3

I really want to use only the Perl functions to make my more Perlish, but I can't easily find out how to avoid using system() in this case.

So I wonder, is there any advantage of using Perl Library functions than using the system() call? Which is the better way?

Answer 1

Often the advantage in using library functions is that you can give meaningful error messages when something goes wrong.

For short-lived scripts or when development resources are at a premium, using system instead can make sense.

Answer 2

local $^I;
local @ARGV = qw(file1 file2);
open my $fh, ">", "file3" or die $!;
my %s;

# print {$fh} (LIST) # or using foreach:
print $fh $_ for
  sort
  grep !$s{$_}++,
  <>;

Main advantage is portability and not having system dependencies.

More explicit version,

use List::MoreUtils qw(uniq);
local $^I;
local @ARGV = qw(file1 file2);
open my $fh, ">", "file3" or die $!;

for my $line (sort uniq readline()) {
  print $fh $line;
}

Answer 3

Use perl library. Saves the processor effort in spawning another process. Also able to get better indication when things go wrong.