What is the difference between PS1 and PROMPT_COMMAND

Question

While taking a look at this awesome thread I noticed that some examples use

PS1=\"Blah Blah Blah\"

and some use

PROMPT_CO         


        

Answer 1

From man bash:

PROMPT_COMMAND

If set, the value is executed as a command prior to issuing each primary prompt.

PS1

The value of this parameter is expanded (see PROMPTING below) and used as the primary prompt string. The default value is ''\s-\v\$ ''.

If you simply want to set the prompt string, using PS1 alone is enough:

PS1='user \u on host \h$ '

If you want to do something else just before printing the prompt, use PROMPT_COMMAND. For example, if you want to sync cached writes to disk, you can write:

PROMPT_COMMAND='sync'