Inherited few Perl Script with echo/sed/awk/grep commands in backticks or system. Is it best practice to convert them to Perl or to leave as it is

Unix shell versus Perl argues that it's better to write everything in Perl to begin with (rather than a motley mix of perl/sed/awk/grep).

Re when/if to rewrite working legacy code, I keep a long list of previous PM discussions on that tricky topic at: Re: Strategies for maintenance of horrible code? (Legacy Code References)