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  sub printN($)   { my $format = shift; sub { sprintf $format, @_ } }

...
      -f5    => printN "%.5f",
  );

  my @func_pipeline = grep {$_} map {$functions{"$_"}} @ARGV;
  @ARGV = grep {!$functions{"$_"}} @ARGV;

  sub compose($$) { my ($f, $g) = @_;   sub { $f->( $g->(@_) ) }    }
  sub id          { @_ }; # identity function

  my $composite_fn = reduce {compose($a,$b)} @func_pipeline, \&id;

  print join ' ', map $composite_fn->($_), split while <>;

  #!/usr/bin/perl -l

...
  my $composite_fn = reduce {compose($a,$b)} @func_pipeline, \&id;
  print join ' ', map $composite_fn->($_), split while <>;

  $ echo 1 2 3 | ./calc-pipeline -f4 -power
  2.7183 7.3891 20.0855