`$PROMPT_COMMAND` – Commands to Execute Before Printing The Prompt

$PROMPT_COMMAND is either an array or a regular variable. Each value is executed as a command before the primary prompt $PS1 is executed.

This is only useful for interactive terminals.

Examples

Show number of files in $HOME in the prompt:

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PROMPT_COMMAND='_fileCount=$(ls ~ | wc -l)' 
PS1="$_fileCount files]$ "
# next prompt will display the number of files

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