Is there a possibility to add some text at the end of every command i type in the terminal? For example i type "ps" and after pressing enter, it becomes "ps -a", I type "ls" and it's "ls -a"
It sounds like you want to create an alias in your .bashrc (hidden and located in user home directory)
Just add the following lines to your .bashrc:
alias ls='ls -a' alias ps='ps -a'
and then run the command to source your .bashrc
Doing this will now cause every ls to also show hidden files (files starting with a .) and every ps you run to show all processes except both session leaders and processes not associate with a terminal.