Comment by 1vuio0pswjnm7

Missing semicolon.

   FRED=barney; set | grep FRED

Also there is no need for grep, nevermind grep -F (fgrep), if using printenv.

   FRED=barney printenv FRED

Without semicolon

   sh -c 'FRED=barney set|grep FRED'

   echo 'FRED=barney set|grep ^FRED'|sh