exec is a bult-in command in Bash, so it doesn't have it's own manual. You can find it's usage intructions in the Bash manual.I realized this by typing "man exec" in Fedora Linux. Fedora shows the bash manual with subcommand exec in it.
Fedora developers prefer to make upstream changes instead of applying fixes specifically for Fedora—this ensures that their updates are available to all Linux distributions.
Запитуйте в розробників і пакувальників у Ubuntu. Нам-то звідки знати?
$ help COMMAND
$ help execexec: exec [-cl] [-a name] [command [arguments ...]] [redirection ...] Replace the shell with the given command. Execute COMMAND, replacing this shell with the specified program. ARGUMENTS become the arguments to COMMAND. If COMMAND is not specified, any redirections take effect in the current shell. Options: -a name pass NAME as the zeroth argument to COMMAND -c execute COMMAND with an empty environment -l place a dash in the zeroth argument to COMMAND If the command cannot be executed, a non-interactive shell exits, unless the shell option `execfail' is set. Exit Status: Returns success unless COMMAND is not found or a redirection error occurs.