4.1. PROMPT_COMMAND
Bash provides an environment variable called PROMPT_COMMAND.
The contents of this variable are executed as a regular Bash command just
before Bash displays a prompt.
[21:55:01][giles@nikola:~] PS1="[\u@\h:\w]\$ "
[giles@nikola:~] PROMPT_COMMAND="date +%H%M"
2155
[giles@nikola:~] d
bin mail
2156
[giles@nikola:~] |
What happened above was that I changed PS1 to no longer include the
\t escape sequence (added in a previous section), so
the time was no longer a part of the prompt. Then I used date
+%H%M to display the time in a format I like better. But it
appears on a different line than the prompt. Tidying this up using
echo -n ... as shown below works with Bash 2.0+, but
appears not to work with Bash 1.14.7: apparently the prompt is drawn in a
different way, and the following method results in overlapping text.
2156
[giles@nikola:~] PROMPT_COMMAND="echo -n [$(date +%H%M)]"
[2156][giles@nikola:~]$
[2156][giles@nikola:~]$ d
bin mail
[2157][giles@nikola:~]$ unset PROMPT_COMMAND
[giles@nikola:~] |
echo -n ... controls the output of the
date command and suppresses the trailing newline,
allowing the prompt to appear all on one line. At the end, I used the
unset command to remove the
PROMPT_COMMAND environment variable.