mjhjmtu

An alias, such as ll is defined with the alias command.

I can check the command with things like type ll which prints

ll is aliased to `ls -l --color=auto'

or command -v ll which prints

alias ll='ls -l --color=auto'

or alias ll which also prints

alias ll='ls -l --color=auto'

but I can't seem to find where the alias was defined, i.e. a file such as .bashrc, or perhaps manually in the running shell. At this point I'm unsure if this is even possible.

Should I simply go through all files that are loaded by bash and check every one of them?

Manual definition will be hard to spot (the history logs, maybe) though asking the shell to show what it is doing and then grep should help find those set in a rc file:

bash -ixlc : 2>&1 | grep ...
zsh -ixc : 2>&1 | grep ...

If the shell isn't precisely capturing the necessary options with one of the above invocations (that interactively run the null command), then script:

script somethingtogrep thatstrangeshell -x
...
grep ... somethingtogrep

Another option would be to use something like strace or sysdig to find all the files the shell touches, then go grep those manually (handy if the shell or program does not have an -x flag); the standard RC files are not sufficient for a manual filename check if something like oh-my-zsh or site-specific configurations are pulling in code from who knows where (or also there may be environment variables, as sorontar points out in their answer).

Here is where I find grep -rl very useful:

grep -rl alias ~/.bash* ~/.profile /etc/profile /etc/bash.bashrc

will tell you in which file the word alias is used.

Probably in ~/.bashrc and most certainly in ~/.bash_aliases if it exists.

It is however impossible to be absolutely sure that that covers all options.
Those files may also call or load any other files.
An environment variable like ENV or $BASH_ENV may direct bash to load some other files.

looks for the variable BASH_ENV in the environment, expands its value if it appears there, and uses the expanded value as the name of a file to read and execute.

And aliases may even be defined by setting a variable (emphasis mine):

BASH_ALIASES

An associative array variable whose members correspond to the internal list of aliases as maintained by the alias builtin. Elements added to this array appear in the alias list

I don't know of a way to actually list the source of your aliases, but since it looks like you're using bash I think these are the possible source files:

/etc/profile
~/.profile
/etc/bash.bashrc
~/.bash_profile
~/.bashrc

You should be able to grep through those to find the alias, e.g. grep 'ls -l --color=auto' /etc/profile ~/.profile /etc/bash.bashrc ~/.bash_profile ~/.bashrc.

I've had success simply using which.

[crclayton@pc scripts]$ which foo
foo: aliased to python $HOME/projects/python/foo.py

Combining thrig's answer with @MarkPlotnick's suggestion, you can test whether BASH_ALIASES[ll] is set to narrow it down. The BASH_SOURCE array and LINENO variables are particularly useful here. Unfortunately, the check whether BASH_ALIASES[ll] is set will only succeed after the alias has been set, and so the first such line could be in another file altogether.

PS4='$BASH_ALIASES["ll"]+"The ll alias has been defined before" $BASH_SOURCE:$LINENO ' bash -lixc : |&
 grep 'll alias' -m1 -B1

Giving output like:

 /home/muru/.bash_aliases:1 alias 'll=ls -AlhF'
TThe ll alias has been defined before /home/muru/.bashrc:116 alias 'ping=ping -c5'

You can even terminate the shell using this check:

$ PS4='$BASH_ALIASES["ll"]+"$(kill -9 $$)" $BASH_SOURCE:$LINENO ' bash -lixc : |& tail -n1
 /home/muru/.bash_aliases:1 alias 'll=ls -AlhF'

Check ~/.profile if it's not in ~/.bashrc