Você pode usar o recurso de substituição do comando Bash:
python test.py command --option 1 $(<file.txt)
Em man bash
:
Command substitution allows the output of a command to replace
the command name. There are two forms:
$(command)
or
'command'
Bash performs the expansion by executing command and replacing
the command substitution with the standard output of the command,
with any trailing newlines deleted. Embedded newlines are not
deleted, but they may be removed during word splitting. The
command substitution $(cat file) can be replaced by the
equivalent but faster $(< file).