Add Where And Which Are Whence as a Zsh TIL

zsh/where-and-which-are-whence.md

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+# Where And Which Are Whence
+
+I was recently watch some of the commands being run by an AI agent in a coding
+harness. One in particular caught my attention because it wasn't one I was
+familiar with. It was the command `whence`.
+
+The `man zshbuiltins` describe `whence` like so:
+
+> For each name, indicate how it would be interpreted if used as a command name.
+
+I'd describe it myself as a utility for surfacing what a given command name
+corresponds to when it gets executed. For instance, when run against the name
+`cat` in my local setup, I see `bat` which is explained by the alias I set up.
+
+```bash
+❯ whence cat
+bat
+```
+
+There are several flags that can be used with `whence`. The underlying behavior
+for `whence` is what is also used for more familiar commands like `where` and
+`which`.
+
+```
+where [ -wpmsS ] [ -x num ] name ...
+        Equivalent to whence -ca.
+
+which [ -wpamsS ] [ -x num ] name ...
+        Equivalent to whence -c.
+```
+
+I can get a clearer answer that `cat` is an alias with `-c`.
+
+```bash
+❯ whence -c cat
+cat: aliased to bat
+```
+
+And with `-ca`, I can see that `cat` resolves several different times on the
+path with the alias to `bat` taking precedence over all of that.
+
+```bash
+❯ whence -ca cat
+cat: aliased to bat
+/bin/cat
+/bin/cat
+/bin/cat
+/bin/cat
+/bin/cat
+/bin/cat
+```
+
+The other command that uses the underlying `whence` functionality is `type`.
+
+```
+type [ -wfpamsS ] name ...
+        Equivalent to whence -v.
+```
+
+See `man zshbuiltins` for more details. There are more flags which can be used
+to get additional info.