Since bash 4.3 multi-line aliases interact very strangely, especially in
connection with PROMPT_COMMAND.
1. PROMPT_COMMAND is executed after every line in the alias, rather than just
before the prompt is drawn:
alias a=$'echo 1\necho2'
PROMPT_COMMAND='echo $HOSTNAME'
$ a
1
home
2
home
$
2. If PROMPT_COMMAND contains a command substitution (even one that is not
executed!) then only the first line of the alias is executed
alias a=$'echo 1\necho2'
PROMPT_COMMAND='echo ${HOSTNAME-$(hostname)}'
$ a
1
home
$
3. If an alias contains a command substitution (this is regardless of
PROMPT_COMMAND being set) something really non-sensical happens.
alias a=$'echo 1 $(id)\necho 2'
$ a
1 2 id
$
For the end user, replacing any multi-line aliases with ';' delimited ones
should probably work just fine. I can't think of any use-cases where the
behavior of one style would be different from another so maybe multi-line
aliases should be disallowed.
