Personally, I would expect the one-liner to print bash: egrepa: command not found - as it does if entered from command line - but doesn't.

The shell was never invoked, so how can it display an error message? It's up to you to do your own error checking.

$ 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. ))
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