$ perl -e'$res = `egrepa 2>&1`; print "$?:$!\n"; print $res'
-1:No such file or directory
(( Perl tried to execute egrepa, couldn't, and returned an error.
   Perl doesn't output error messages for you. ))

$ perl -e'$res = `egrepa "" 2>&1`; print "$?:$!\n"; print $res'
32512:
sh: egrepa: command not found
(( Perl sees a shell command, and successfully executed the shell.
   The shell couldn't execute egrapa "", so it displayed and 
   returned an error. ))