Bash – How to retrieve lost aliases

From Aliases (section 6.6 of the Bash Manual):

The first word of each simple command, if unquoted, is checked to see if it has an alias. If so, that word is replaced by the text of the alias.

This happens when you use the alias, not when you define it. Here's an example:

$ alias a1='a2 hello'
$ alias a2='echo'
$ a1
hello
$ unalias a2
$ a1
bash: a2: command not found

• alias without parameter outputs the definitions of currently defined aliases.
• declare -f outputs the definitions of currently defined functions.
• export -p outputs the definitions of currently defined variables.

All those commands output definitions ready to be reused, you can redirect their outputs directly to a new ~/.bashrc.

All lists will contain a lot of elements defined elsewhere, for example /etc/profile and /etc/bash_completion. So you will have to clean up the list manually.