Having trouble passing a shell variable to a query from psql command line

Hello,

Below works:

psql -d mydb -t -A -c "SELECT relkind FROM pg_class WHERE relname = 'pg_trigger' ;"

r

I am getting syntax error from following:

echo $SHELL_VAR

pg_trigger

psql -d mydb -t -A -c "SELECT relkind FROM pg_class WHERE relname = :'SHELL_VAR' ;" -v SHELL_VAR="$SHELL_VAR"

ERROR:  syntax error at or near ":"

LINE 1: SELECT relkind FROM pg_class WHERE relname = :'SHELL_VAR' ;

                                                     ^

Is psql script necessary to pass shell variable?

I appreciate any help you can provide.