pgtclsh is a Tcl shell interface extended with Postgres database access functions. (Essentially, it is tclsh with libpgtcl loaded.) Like with the regular Tcl shell, the first command line argument is a script file, any remaining arguments are passed to the script. If no script file is named, the shell is interactive.
A Tcl shell with Tk and Postgres functions is available as pgtksh .
Read the upstream documentation. For corrections, first check the current manual.