Path::Tiny has chomp option :) also "or dies" on error ... here is pretty much the same code

#!/usr/bin/perl --
use strict; use warnings;
use Path::Tiny qw/ path /;
my @lines = path( "splitin.pl" )->lines( { chomp => 1 } );
s/\s+$// for @lines; ## extra "chomp", trim trailing whitespace
s/^\s+// for @lines; ## trim leading whitespace
@lines = grep /^\$outcome /x, @lines;
@lines = map { substr( $_, 10, -2 )."\n" } @lines;
path( "output.csv" )->spew( @lines );
undef @lines;
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