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+#+TITLE: How to get all Emacs daemon buffers from a shell script
+#+DATE: 2021-05-01T22:38:32-04:00
+#+DRAFT: true
+#+DESCRIPTION: A small script that will print all Emacs daemon buffers to stdout
+#+TAGS[]: emacs
+#+KEYWORDS[]: emacs
+#+SLUG:
+#+SUMMARY:
+
+#+ATTR_HTML: :title Emacs daemon buffers
+#+ATTR_HTML: :alt Emacs darmon buffers
+[[file:cover.png]]
+
+A while back I posted a response to someone's question on [[https://www.reddit.com/r/emacs/comments/ljtify/is_it_there_a_way_to_export_the_list_of_opened/gnhatdu/?context=3][reddit]] about
+how to get a list of all Emacs daemon buffers from a shell script. It
+was a pretty interesting problem so I thought I'd explain my answer
+here.
+
+The question was "Is it there a way to export the list of opened
+buffers to STDOUT?".
+
+In the comments I left a rather byzantine looking snippet of code that
+I'd managed to produce.
+
+#+begin_src
+emacs --batch --eval "(require 'server)" --eval "(mapc #'print (read (server-eval-at \"server\" '(format \"%s\" (mapcar (lambda (buffer) (format \"\\\"%s\\\"\n\" buffer)) (buffer-list))))))" | sed '/^$/d; s/^"//g; s/"$//g'
+#+end_src
+
+I've simplified the lisp slightly since I answered that question.
+Here's the updated version.
+
+#+begin_src
+emacs --batch --eval "(require 'server)" --eval "(mapc #'princ (read (server-eval-at \"server\" '(prin1-to-string (mapcar (lambda (buffer) (format \"%s\\n\" buffer)) (buffer-list))))))" 2>/dev/null
+#+end_src
+
+Here it is written in a way that's easier to read.
+
+#+begin_src
+emacs --batch \
+      --eval "(require 'server)" \
+      --eval "(mapc #'princ
+                    (read (server-eval-at \"server\"
+                             '(prin1-to-string (mapcar (lambda (buffer)
+                                                           (format \"%s\\n\" buffer))
+                                                       (buffer-list))))))" \
+      2>/dev/null
+#+end_src
+
+
+Let's break it down.
+
+- =emacs= Emacs itself!
+  - =--batch= Runs Emacs in [[https://www.gnu.org/software/emacs/manual/html_node/elisp/Batch-Mode.html][=batch=]] mode, which executes commands
+    non-interactively and stops it from opening a window. This is
+    usually used for running Emacs lisp as a script.
+  - =--eval= Evaluates the following piece of elisp in the batch Emacs
+    - =(require 'server)= Loads the built-in =server= package. This is
+      used to connect to the running Emacs daemon
+  - =--eval= Since the previous elisp snippet was a complete
+    s-expression I evaluate the next expression as a new argument. I
+    could have also wrapped them both in a =progn=, but this felt cleaner.
+    - =mapc FUNCTION SEQUENCE= Apply =FUNCTION= to every object in the
+      list =SEQUENCE=.
+      - =princ= Outputs the printed form of an object to
+        =standard-out=. It's used here because it doesn't surround the
+        string in quotes like =print= does.
+      - =read STREAM= Read =STREAM=, in this case a string, and turn it
+        into a lisp object
+        - =server-eval-at \"server\" FORM= Evaluates =FORM= on the Emacs
+          daemon and returns the result. The quotes are escaped
+          because it's already inside a quote because it's a command
+          line argument.
+          - =prin1-to-string OBJECT= Return a string containing the
+            printed representation of =OBJECT=. I use this instead of
+            =princ= because that outputs the result to the minibuffer of
+            the Emacs daemon instead of returning it.
+            - =mapcar FUNCTION SEQUENCE= Applies FUNCTION to each
+              element of SEQUENCE and returns a list of the result.
+              - =(lambda (buffer) (format \"%s\\n\" buffer)= An
+                anonymous function that takes a buffer and returns the
+                string version of its name followed by a newline. The
+                quotes and newline are escaped because it's already
+                inside a quote because it's a command line argument.
+              - =buffer-list= Returns a list of all buffers in Emacs
+  - =2>/dev/null= Send the Emacs startup text, which is outputted to
+    =stderr=, to =/dev/null=. We don't want to see it.
+
+The result is a single line command that outputs the name of every
+buffer in the Emacs daemon, one per line, to =stdout=.