How to call a script after every bash command

Question

Is it possible to call a script in this example named hey.sh after every bash command?

For example you type ls hit enter and ls runs, then hey.sh would run.

You then type cd .. (or any other command), cd runs then hey.sh would run, and so on.

Answer 1

PROMPT_COMMAND+="hey.sh;"

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

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Note: Environment variables vs shell variables

By default, PROMPT_COMMAND is not an environment variable. It's just a shell variable.

Both types of variables are accessed the same way ("$variable*"), but environment variables are inherited by child processes whereas shell variables aren't.

The convention is to capitalize environment variables + shell variables that configure your shell (PROMPT_COMMAND does configure your shell), but keep other types of variables lower case.

In bash, you can do: declare -p to find out whether a variable is exported (=is an environment variable) or not:

$ declare -p PATH
declare -x PATH=... #-x means it's exported
$ declare PROMPT_COMMAND
declare -- PROMPT_COMMAND=... #no -x so just a shell variable